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package ExtUtils::Constant::Base; use strict; use vars qw($VERSION); use Carp; use Text::Wrap; use ExtUtils::Constant::Utils qw(C_stringify perl_stringify); $VERSION = '0.05'; use constant is_perl56 => ($] < 5.007 && $] > 5.005_50); =head1 NAME ExtUtils::Constant::Base - base class for ExtUtils::Constant objects =head1 SYNOPSIS require ExtUtils::Constant::Base; @ISA = 'ExtUtils::Constant::Base'; =head1 DESCRIPTION ExtUtils::Constant::Base provides a base implementation of methods to generate C code to give fast constant value lookup by named string. Currently it's mostly used ExtUtils::Constant::XS, which generates the lookup code for the constant() subroutine found in many XS modules. =head1 USAGE ExtUtils::Constant::Base exports no subroutines. The following methods are available =over 4 =cut sub valid_type { # Default to assuming that you don't need different types of return data. 1; } sub default_type { ''; } =item header A method returning a scalar containing definitions needed, typically for a C header file. =cut sub header { '' } # This might actually be a return statement. Note that you are responsible # for any space you might need before your value, as it lets to perform # "tricks" such as "return KEY_" and have strings appended. sub assignment_clause_for_type; # In which case this might be an empty string sub return_statement_for_type {undef}; sub return_statement_for_notdef; sub return_statement_for_notfound; # "#if 1" is true to a C pre-processor sub macro_from_name { 1; } sub macro_from_item { 1; } sub macro_to_ifdef { my ($self, $macro) = @_; if (ref $macro) { return $macro->[0]; } if (defined $macro && $macro ne "" && $macro ne "1") { return $macro ? "#ifdef $macro\n" : "#if 0\n"; } return ""; } sub macro_to_ifndef { my ($self, $macro) = @_; if (ref $macro) { # Can't invert these stylishly, so "bodge it" return "$macro->[0]#else\n"; } if (defined $macro && $macro ne "" && $macro ne "1") { return $macro ? "#ifndef $macro\n" : "#if 1\n"; } croak "Can't generate an ifndef for unconditional code"; } sub macro_to_endif { my ($self, $macro) = @_; if (ref $macro) { return $macro->[1]; } if (defined $macro && $macro ne "" && $macro ne "1") { return "#endif\n"; } return ""; } sub name_param { 'name'; } # This is possibly buggy, in that it's not mandatory (below, in the main # C_constant parameters, but is expected to exist here, if it's needed) # Buggy because if you're definitely pure 8 bit only, and will never be # presented with your constants in utf8, the default form of C_constant can't # be told not to do the utf8 version. sub is_utf8_param { 'utf8'; } sub memEQ { "!memcmp"; } =item memEQ_clause args_hashref A method to return a suitable C C<if> statement to check whether I<name> is equal to the C variable C<name>. If I<checked_at> is defined, then it is used to avoid C<memEQ> for short names, or to generate a comment to highlight the position of the character in the C<switch> statement. If i<checked_at> is a reference to a scalar, then instead it gives the characters pre-checked at the beginning, (and the number of chars by which the C variable name has been advanced. These need to be chopped from the front of I<name>). =cut sub memEQ_clause { # if (memEQ(name, "thingy", 6)) { # Which could actually be a character comparison or even "" my ($self, $args) = @_; my ($name, $checked_at, $indent) = @{$args}{qw(name checked_at indent)}; $indent = ' ' x ($indent \|\| 4); my $front_chop; if (ref $checked_at) { # regexp won't work on 5.6.1 without use utf8; in turn that won't work # on 5.005_03. substr ($name, 0, length $$checked_at,) = ''; $front_chop = C_stringify ($$checked_at); undef $checked_at; } my $len = length $name; if ($len < 2) { return $indent . "{\n" if (defined $checked_at and $checked_at == 0) or $len == 0; # We didn't switch, drop through to the code for the 2 character string $checked_at = 1; } my $name_param = $self->name_param; if ($len < 3 and defined $checked_at) { my $check; if ($checked_at == 1) { $check = 0; } elsif ($checked_at == 0) { $check = 1; } if (defined $check) { my $char = C_stringify (substr $name, $check, 1); # Placate 5.005 with a break in the string. I can't see a good way of # getting it to not take [ as introducing an array lookup, even with # ${name_param}[$check] return $indent . "if ($name_param" . "[$check] == '$char') {\n"; } } if (($len == 2 and !defined $checked_at) or ($len == 3 and defined ($checked_at) and $checked_at == 2)) { my $char1 = C_stringify (substr $name, 0, 1); my $char2 = C_stringify (substr $name, 1, 1); return $indent . "if ($name_param" . "[0] == '$char1' && $name_param" . "[1] == '$char2') {\n"; } if (($len == 3 and defined ($checked_at) and $checked_at == 1)) { my $char1 = C_stringify (substr $name, 0, 1); my $char2 = C_stringify (substr $name, 2, 1); return $indent . "if ($name_param" . "[0] == '$char1' && $name_param" . "[2] == '$char2') {\n"; } my $pointer = '^'; my $have_checked_last = defined ($checked_at) && $len == $checked_at + 1; if ($have_checked_last) { # Checked at the last character, so no need to memEQ it. $pointer = C_stringify (chop $name); $len--; } $name = C_stringify ($name); my $memEQ = $self->memEQ(); my $body = $indent . "if ($memEQ($name_param, \"$name\", $len)) {\n"; # Put a little ^ under the letter we checked at # Screws up for non printable and non-7 bit stuff, but that's too hard to # get right. if (defined $checked_at) { $body .= $indent . "/* " . (' ' x length $memEQ) . (' ' x length $name_param) . (' ' x $checked_at) . $pointer . (' ' x ($len - $checked_at + length $len)) . " /\n"; } elsif (defined $front_chop) { $body .= $indent . "/ $front_chop" . (' ' x ($len + 1 + length $len)) . " /\n"; } return $body; } =item dump_names arg_hashref, ITEM... An internal function to generate the embedded perl code that will regenerate the constant subroutines. I<default_type>, I<types> and I<ITEM>s are the same as for C_constant. I<indent> is treated as number of spaces to indent by. If C<declare_types> is true a C<$types> is always declared in the perl code generated, if defined and false never declared, and if undefined C<$types> is only declared if the values in I<types> as passed in cannot be inferred from I<default_types> and the I<ITEM>s. =cut sub dump_names { my ($self, $args, @items) = @_; my ($default_type, $what, $indent, $declare_types) = @{$args}{qw(default_type what indent declare_types)}; $indent = ' ' x ($indent \|\| 0); my $result; my (@simple, @complex, %used_types); foreach (@items) { my $type; if (ref $_) { $type = $_->{type} \|\| $default_type; if ($_->{utf8}) { # For simplicity always skip the bytes case, and reconstitute this entry # from its utf8 twin. next if $_->{utf8} eq 'no'; # Copy the hashref, as we don't want to mess with the caller's hashref. $_ = {%$_}; unless (is_perl56) { utf8::decode ($_->{name}); } else { $_->{name} = pack 'U', unpack 'U0U', $_->{name}; } delete $_->{utf8}; } } else { $_ = {name=>$_}; $type = $default_type; } $used_types{$type}++; if ($type eq $default_type # grr 5.6.1 and length $_->{name} and length $_->{name} == ($_->{name} =~ tr/A-Za-z0-9_//) and !defined ($_->{macro}) and !defined ($_->{value}) and !defined ($_->{default}) and !defined ($_->{pre}) and !defined ($_->{post}) and !defined ($_->{def_pre}) and !defined ($_->{def_post}) and !defined ($_->{weight})) { # It's the default type, and the name consists only of A-Za-z0-9_ push @simple, $_->{name}; } else { push @complex, $_; } } if (!defined $declare_types) { # Do they pass in any types we weren't already using? foreach (keys %$what) { next if $used_types{$_}; $declare_types++; # Found one in $what that wasn't used. last; # And one is enough to terminate this loop } } if ($declare_types) { $result = $indent . 'my $types = {map {($_, 1)} qw(' . join (" ", sort keys %$what) . ")};\n"; } local $Text::Wrap::huge = 'overflow'; local $Text::Wrap::columns = 80; $result .= wrap ($indent . "my \@names = (qw(", $indent . " ", join (" ", sort @simple) . ")"); if (@complex) { foreach my $item (sort {$a->{name} cmp $b->{name}} @complex) { my $name = perl_stringify $item->{name}; my $line = ",\n$indent {name=>\"$name\""; $line .= ", type=>\"$item->{type}\"" if defined $item->{type}; foreach my $thing (qw (macro value default pre post def_pre def_post)) { my $value = $item->{$thing}; if (defined $value) { if (ref $value) { $line .= ", $thing=>[\"" . join ('", "', map {perl_stringify $_} @$value) . '"]'; } else { $line .= ", $thing=>\"" . perl_stringify($value) . "\""; } } } $line .= "}"; # Ensure that the enclosing C comment doesn't end # by turning / into " . "/ $line =~ s!\\/!\" . "/!gs; # gcc -Wall doesn't like finding / inside a comment $line =~ s!\/\!/" . "\!gs; $result .= $line; } } $result .= ");\n"; $result; } =item assign arg_hashref, VALUE... A method to return a suitable assignment clause. If I<type> is aggregate (eg I<PVN> expects both pointer and length) then there should be multiple I<VALUE>s for the components. I<pre> and I<post> if defined give snippets of C code to proceed and follow the assignment. I<pre> will be at the start of a block, so variables may be defined in it. =cut # Hmm. value undef to to NOTDEF? value () to do NOTFOUND? sub assign { my $self = shift; my $args = shift; my ($indent, $type, $pre, $post, $item) = @{$args}{qw(indent type pre post item)}; $post \|\|= ''; my $clause; my $close; if ($pre) { chomp $pre; $close = "$indent}\n"; $clause = $indent . "{\n"; $indent .= " "; $clause .= "$indent$pre"; $clause .= ";" unless $pre =~ /;$/; $clause .= "\n"; } confess "undef \$type" unless defined $type; confess "Can't generate code for type $type" unless $self->valid_type($type); $clause .= join '', map {"$indent$_\n"} $self->assignment_clause_for_type({type=>$type,item=>$item}, @_); chomp $post; if (length $post) { $clause .= "$post"; $clause .= ";" unless $post =~ /;$/; $clause .= "\n"; } my $return = $self->return_statement_for_type($type); $clause .= "$indent$return\n" if defined $return; $clause .= $close if $close; return $clause; } =item return_clause arg_hashref, ITEM A method to return a suitable C<#ifdef> clause. I<ITEM> is a hashref (as passed to C<C_constant> and C<match_clause>. I<indent> is the number of spaces to indent, defaulting to 6. =cut sub return_clause { ##ifdef thingy # iv_return = thingy; # return PERL_constant_ISIV; ##else # return PERL_constant_NOTDEF; ##endif my ($self, $args, $item) = @_; my $indent = $args->{indent}; my ($name, $value, $default, $pre, $post, $def_pre, $def_post, $type) = @$item{qw (name value default pre post def_pre def_post type)}; $value = $name unless defined $value; my $macro = $self->macro_from_item($item); $indent = ' ' x ($indent \|\| 6); unless (defined $type) { # use Data::Dumper; print STDERR Dumper ($item); confess "undef \$type"; } ##ifdef thingy my $clause = $self->macro_to_ifdef($macro); # iv_return = thingy; # return PERL_constant_ISIV; $clause .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre, post=>$post, item=>$item}, ref $value ? @$value : $value); if (defined $macro && $macro ne "" && $macro ne "1") { ##else $clause .= "#else\n"; # return PERL_constant_NOTDEF; if (!defined $default) { my $notdef = $self->return_statement_for_notdef(); $clause .= "$indent$notdef\n" if defined $notdef; } else { my @default = ref $default ? @$default : $default; $type = shift @default; $clause .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre, post=>$post, item=>$item}, @default); } } ##endif $clause .= $self->macro_to_endif($macro); return $clause; } sub match_clause { # $offset defined if we have checked an offset. my ($self, $args, $item) = @_; my ($offset, $indent) = @{$args}{qw(checked_at indent)}; $indent = ' ' x ($indent \|\| 4); my $body = ''; my ($no, $yes, $either, $name, $inner_indent); if (ref $item eq 'ARRAY') { ($yes, $no) = @$item; $either = $yes \|\| $no; confess "$item is $either expecting hashref in [0] \|\| [1]" unless ref $either eq 'HASH'; $name = $either->{name}; } else { confess "$item->{name} has utf8 flag '$item->{utf8}', should be false" if $item->{utf8}; $name = $item->{name}; $inner_indent = $indent; } $body .= $self->memEQ_clause ({name => $name, checked_at => $offset, indent => length $indent}); # If we've been presented with an arrayref for $item, then the user string # contains in the range 128-255, and we need to check whether it was utf8 # (or not). # In the worst case we have two named constants, where one's name happens # encoded in UTF8 happens to be the same byte sequence as the second's # encoded in (say) ISO-8859-1. # In this case, $yes and $no both have item hashrefs. if ($yes) { $body .= $indent . " if (" . $self->is_utf8_param . ") {\n"; } elsif ($no) { $body .= $indent . " if (!" . $self->is_utf8_param . ") {\n"; } if ($either) { $body .= $self->return_clause ({indent=>4 + length $indent}, $either); if ($yes and $no) { $body .= $indent . " } else {\n"; $body .= $self->return_clause ({indent=>4 + length $indent}, $no); } $body .= $indent . " }\n"; } else { $body .= $self->return_clause ({indent=>2 + length $indent}, $item); } $body .= $indent . "}\n"; } =item switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM... An internal method to generate a suitable C<switch> clause, called by C<C_constant> I<ITEM>s are in the hash ref format as given in the description of C<C_constant>, and must all have the names of the same length, given by I<NAMELEN>. I<ITEMHASH> is a reference to a hash, keyed by name, values being the hashrefs in the I<ITEM> list. (No parameters are modified, and there can be keys in the I<ITEMHASH> that are not in the list of I<ITEM>s without causing problems - the hash is passed in to save generating it afresh for each call). =cut sub switch_clause { my ($self, $args, $namelen, $items, @items) = @_; my ($indent, $comment) = @{$args}{qw(indent comment)}; $indent = ' ' x ($indent \|\| 2); local $Text::Wrap::huge = 'overflow'; local $Text::Wrap::columns = 80; my @names = sort map {$_->{name}} @items; my $leader = $indent . '/* '; my $follower = ' ' x length $leader; my $body = $indent . "/* Names all of length $namelen. /\n"; if (defined $comment) { $body = wrap ($leader, $follower, $comment) . "\n"; $leader = $follower; } my @safe_names = @names; foreach (@safe_names) { confess sprintf "Name '$_' is length %d, not $namelen", length unless length == $namelen; # Argh. 5.6.1 # next unless tr/A-Za-z0-9_//c; next if tr/A-Za-z0-9_// == length; $_ = '"' . perl_stringify ($_) . '"'; # Ensure that the enclosing C comment doesn't end # by turning / into " . "/ s!\\/!\"."/!gs; # gcc -Wall doesn't like finding / inside a comment s!\/\!/"."\!gs; } $body .= wrap ($leader, $follower, join (" ", @safe_names) . " /") . "\n"; # Figure out what to switch on. # (RMS, Spread of jump table, Position, Hashref) my @best = (1e38, ~0); # Prefer the last character over the others. (As it lets us shorten the # memEQ clause at no cost). foreach my $i ($namelen - 1, 0 .. ($namelen - 2)) { my ($min, $max) = (~0, 0); my %spread; if (is_perl56) { # Need proper Unicode preserving hash keys for bytes in range 128-255 # here too, for some reason. grr 5.6.1 yet again. tie %spread, 'ExtUtils::Constant::Aaargh56Hash'; } foreach (@names) { my $char = substr $_, $i, 1; my $ord = ord $char; confess "char $ord is out of range" if $ord > 255; $max = $ord if $ord > $max; $min = $ord if $ord < $min; push @{$spread{$char}}, $_; # warn "$_ $char"; } # I'm going to pick the character to split on that minimises the root # mean square of the number of names in each case. Normally this should # be the one with the most keys, but it may pick a 7 where the 8 has # one long linear search. I'm not sure if RMS or just sum of squares is # actually better. # $max and $min are for the tie-breaker if the root mean squares match. # Assuming that the compiler may be building a jump table for the # switch() then try to minimise the size of that jump table. # Finally use < not <= so that if it still ties the earliest part of # the string wins. Because if that passes but the memEQ fails, it may # only need the start of the string to bin the choice. # I think. But I'm micro-optimising. :-) # OK. Trump that. Now favour the last character of the string, before the # rest. my $ss; $ss += @$_ @$_ foreach values %spread; my $rms = sqrt ($ss / keys %spread); if ($rms < $best[0] \|\| ($rms == $best[0] && ($max - $min) < $best[1])) { @best = ($rms, $max - $min, $i, \%spread); } } confess "Internal error. Failed to pick a switch point for @names" unless defined $best[2]; # use Data::Dumper; print Dumper (@best); my ($offset, $best) = @best[2,3]; $body .= $indent . "/* Offset $offset gives the best switch position. /\n"; my $do_front_chop = $offset == 0 && $namelen > 2; if ($do_front_chop) { $body .= $indent . "switch (" . $self->name_param() . "++) {\n"; } else { $body .= $indent . "switch (" . $self->name_param() . "[$offset]) {\n"; } foreach my $char (sort keys %$best) { confess sprintf "'$char' is %d bytes long, not 1", length $char if length ($char) != 1; confess sprintf "char %#X is out of range", ord $char if ord ($char) > 255; $body .= $indent . "case '" . C_stringify ($char) . "':\n"; foreach my $thisone (sort { # Deal with the case of an item actually being an array ref to 1 or 2 # hashrefs. Don't assign to $a or $b, as they're aliases to the orignal my $l = ref $a eq 'ARRAY' ? ($a->[0] \|\| $->[1]) : $a; my $r = ref $b eq 'ARRAY' ? ($b->[0] \|\| $->[1]) : $b; # Sort by weight first ($r->{weight} \|\| 0) <=> ($l->{weight} \|\| 0) # Sort equal weights by name or $l->{name} cmp $r->{name}} # If this looks evil, maybe it is. $items is a # hashref, and we're doing a hash slice on it @{$items}{@{$best->{$char}}}) { # warn "You are here"; if ($do_front_chop) { $body .= $self->match_clause ({indent => 2 + length $indent, checked_at => \$char}, $thisone); } else { $body .= $self->match_clause ({indent => 2 + length $indent, checked_at => $offset}, $thisone); } } $body .= $indent . " break;\n"; } $body .= $indent . "}\n"; return $body; } sub C_constant_return_type { "static int"; } sub C_constant_prefix_param { ''; } sub C_constant_prefix_param_defintion { ''; } sub name_param_definition { "const char " . $_[0]->name_param; } sub namelen_param { 'len'; } sub namelen_param_definition { 'size_t ' . $_[0]->namelen_param; } sub C_constant_other_params { ''; } sub C_constant_other_params_defintion { ''; } =item params WHAT An "internal" method, subject to change, currently called to allow an overriding class to cache information that will then be passed into all the C<param> calls. (Yes, having to read the source to make sense of this is considered a known bug). I<WHAT> is be a hashref of types the constant function will return. In ExtUtils::Constant::XS this method is used to returns a hashref keyed IV NV PV SV to show which combination of pointers will be needed in the C argument list generated by C_constant_other_params_definition and C_constant_other_params =cut sub params { ''; } =item dogfood arg_hashref, ITEM... An internal function to generate the embedded perl code that will regenerate the constant subroutines. Parameters are the same as for C_constant. Currently the base class does nothing and returns an empty string. =cut sub dogfood { '' } =item normalise_items args, default_type, seen_types, seen_items, ITEM... Convert the items to a normalised form. For 8 bit and Unicode values converts the item to an array of 1 or 2 items, both 8 bit and UTF-8 encoded. =cut sub normalise_items { my $self = shift; my $args = shift; my $default_type = shift; my $what = shift; my $items = shift; my @new_items; foreach my $orig (@_) { my ($name, $item); if (ref $orig) { # Make a copy which is a normalised version of the ref passed in. $name = $orig->{name}; my ($type, $macro, $value) = @$orig{qw (type macro value)}; $type \|\|= $default_type; $what->{$type} = 1; $item = {name=>$name, type=>$type}; undef $macro if defined $macro and $macro eq $name; $item->{macro} = $macro if defined $macro; undef $value if defined $value and $value eq $name; $item->{value} = $value if defined $value; foreach my $key (qw(default pre post def_pre def_post weight not_constant)) { my $value = $orig->{$key}; $item->{$key} = $value if defined $value; # warn "$key $value"; } } else { $name = $orig; $item = {name=>$name, type=>$default_type}; $what->{$default_type} = 1; } warn +(ref ($self) \|\| $self) . "doesn't know how to handle values of type $_ used in macro $name" unless $self->valid_type ($item->{type}); # tr///c is broken on 5.6.1 for utf8, so my original tr/\0-\177//c # doesn't work. Upgrade to 5.8 # if ($name !~ tr/\0-\177//c \|\| $] < 5.005_50) { if ($name =~ tr/\0-\177// == length $name \|\| $] < 5.005_50 \|\| $args->{disable_utf8_duplication}) { # No characters outside 7 bit ASCII. if (exists $items->{$name}) { die "Multiple definitions for macro $name"; } $items->{$name} = $item; } else { # No characters outside 8 bit. This is hardest. if (exists $items->{$name} and ref $items->{$name} ne 'ARRAY') { confess "Unexpected ASCII definition for macro $name"; } # Again, 5.6.1 tr broken, so s/5\.6./5\.8\.0/; # if ($name !~ tr/\0-\377//c) { if ($name =~ tr/\0-\377// == length $name) { # if ($] < 5.007) { # $name = pack "C", unpack "U", $name; # } $item->{utf8} = 'no'; $items->{$name}[1] = $item; push @new_items, $item; # Copy item, to create the utf8 variant. $item = {%$item}; } # Encode the name as utf8 bytes. unless (is_perl56) { utf8::encode($name); } else { # warn "Was >$name< " . length ${name}; $name = pack 'C', unpack 'C', $name . pack 'U'; # warn "Now '${name}' " . length ${name}; } if ($items->{$name}[0]) { die "Multiple definitions for macro $name"; } $item->{utf8} = 'yes'; $item->{name} = $name; $items->{$name}[0] = $item; # We have need for the utf8 flag. $what->{''} = 1; } push @new_items, $item; } @new_items; } =item C_constant arg_hashref, ITEM... A function that returns a B<list> of C subroutine definitions that return the value and type of constants when passed the name by the XS wrapper. I<ITEM...> gives a list of constant names. Each can either be a string, which is taken as a C macro name, or a reference to a hash with the following keys =over 8 =item name The name of the constant, as seen by the perl code. =item type The type of the constant (I<IV>, I<NV> etc) =item value A C expression for the value of the constant, or a list of C expressions if the type is aggregate. This defaults to the I<name> if not given. =item macro The C pre-processor macro to use in the C<#ifdef>. This defaults to the I<name>, and is mainly used if I<value> is an C<enum>. If a reference an array is passed then the first element is used in place of the C<#ifdef> line, and the second element in place of the C<#endif>. This allows pre-processor constructions such as #if defined (foo) #if !defined (bar) ... #endif #endif to be used to determine if a constant is to be defined. A "macro" 1 signals that the constant is always defined, so the C<#if>/C<#endif> test is omitted. =item default Default value to use (instead of C<croak>ing with "your vendor has not defined...") to return if the macro isn't defined. Specify a reference to an array with type followed by value(s). =item pre C code to use before the assignment of the value of the constant. This allows you to use temporary variables to extract a value from part of a C<struct> and return this as I<value>. This C code is places at the start of a block, so you can declare variables in it. =item post C code to place between the assignment of value (to a temporary) and the return from the function. This allows you to clear up anything in I<pre>. Rarely needed. =item def_pre =item def_post Equivalents of I<pre> and I<post> for the default value. =item utf8 Generated internally. Is zero or undefined if name is 7 bit ASCII, "no" if the name is 8 bit (and so should only match if SvUTF8() is false), "yes" if the name is utf8 encoded. The internals automatically clone any name with characters 128-255 but none 256+ (ie one that could be either in bytes or utf8) into a second entry which is utf8 encoded. =item weight Optional sorting weight for names, to determine the order of linear testing when multiple names fall in the same case of a switch clause. Higher comes earlier, undefined defaults to zero. =back In the argument hashref, I<package> is the name of the package, and is only used in comments inside the generated C code. I<subname> defaults to C<constant> if undefined. I<default_type> is the type returned by C<ITEM>s that don't specify their type. It defaults to the value of C<default_type()>. I<types> should be given either as a comma separated list of types that the C subroutine I<subname> will generate or as a reference to a hash. I<default_type> will be added to the list if not present, as will any types given in the list of I<ITEM>s. The resultant list should be the same list of types that C<XS_constant> is given. [Otherwise C<XS_constant> and C<C_constant> may differ in the number of parameters to the constant function. I<indent> is currently unused and ignored. In future it may be used to pass in information used to change the C indentation style used.] The best way to maintain consistency is to pass in a hash reference and let this function update it. I<breakout> governs when child functions of I<subname> are generated. If there are I<breakout> or more I<ITEM>s with the same length of name, then the code to switch between them is placed into a function named I<subname>_I<len>, for example C<constant_5> for names 5 characters long. The default I<breakout> is 3. A single C<ITEM> is always inlined. =cut # The parameter now BREAKOUT was previously documented as: # # I<NAMELEN> if defined signals that all the I<name>s of the I<ITEM>s are of # this length, and that the constant name passed in by perl is checked and # also of this length. It is used during recursion, and should be C<undef> # unless the caller has checked all the lengths during code generation, and # the generated subroutine is only to be called with a name of this length. # # As you can see it now performs this function during recursion by being a # scalar reference. sub C_constant { my ($self, $args, @items) = @_; my ($package, $subname, $default_type, $what, $indent, $breakout) = @{$args}{qw(package subname default_type types indent breakout)}; $package \|\|= 'Foo'; $subname \|\|= 'constant'; # I'm not using this. But a hashref could be used for full formatting without # breaking this API # $indent \|\|= 0; my ($namelen, $items); if (ref $breakout) { # We are called recursively. We trust @items to be normalised, $what to # be a hashref, and pinch %$items from our parent to save recalculation. ($namelen, $items) = @$breakout; } else { $items = {}; if (is_perl56) { # Need proper Unicode preserving hash keys. require ExtUtils::Constant::Aaargh56Hash; tie %$items, 'ExtUtils::Constant::Aaargh56Hash'; } $breakout \|\|= 3; $default_type \|\|= $self->default_type(); if (!ref $what) { # Convert line of the form IV,UV,NV to hash $what = {map {$_ => 1} split /,\s/, ($what \|\| '')}; # Figure out what types we're dealing with, and assign all unknowns to the # default type } @items = $self->normalise_items ({}, $default_type, $what, $items, @items); # use Data::Dumper; print Dumper @items; } my $params = $self->params ($what); # Probably "static int" my ($body, @subs); $body = $self->C_constant_return_type($params) . "\n$subname (" # Eg "pTHX_ " . $self->C_constant_prefix_param_defintion($params) # Probably "const char name" . $self->name_param_definition($params); # Something like ", STRLEN len" $body .= ", " . $self->namelen_param_definition($params) unless defined $namelen; $body .= $self->C_constant_other_params_defintion($params); $body .= ") {\n"; if (defined $namelen) { # We are a child subroutine. Print the simple description my $comment = 'When generated this function returned values for the list' . ' of names given here. However, subsequent manual editing may have' . ' added or removed some.'; $body .= $self->switch_clause ({indent=>2, comment=>$comment}, $namelen, $items, @items); } else { # We are the top level. $body .= " / Initially switch on the length of the name. */\n"; $body .= $self->dogfood ({package => $package, subname => $subname, default_type => $default_type, what => $what, indent => $indent, breakout => $breakout}, @items); $body .= ' switch ('.$self->namelen_param().") {\n"; # Need to group names of the same length my @by_length; foreach (@items) { push @{$by_length[length $_->{name}]}, $_; } foreach my $i (0 .. $#by_length) { next unless $by_length[$i]; # None of this length $body .= " case $i:\n"; if (@{$by_length[$i]} == 1) { my $only_thing = $by_length[$i]->[0]; if ($only_thing->{utf8}) { if ($only_thing->{utf8} eq 'yes') { # With utf8 on flag item is passed in element 0 $body .= $self->match_clause (undef, [$only_thing]); } else { # With utf8 off flag item is passed in element 1 $body .= $self->match_clause (undef, [undef, $only_thing]); } } else { $body .= $self->match_clause (undef, $only_thing); } } elsif (@{$by_length[$i]} < $breakout) { $body .= $self->switch_clause ({indent=>4}, $i, $items, @{$by_length[$i]}); } else { # Only use the minimal set of parameters actually needed by the types # of the names of this length. my $what = {}; foreach (@{$by_length[$i]}) { $what->{$_->{type}} = 1; $what->{''} = 1 if $_->{utf8}; } $params = $self->params ($what); push @subs, $self->C_constant ({package=>$package, subname=>"${subname}_$i", default_type => $default_type, types => $what, indent => $indent, breakout => [$i, $items]}, @{$by_length[$i]}); $body .= " return ${subname}_$i (" # Eg "aTHX_ " . $self->C_constant_prefix_param($params) # Probably "name" . $self->name_param($params); $body .= $self->C_constant_other_params($params); $body .= ");\n"; } $body .= " break;\n"; } $body .= " }\n"; } my $notfound = $self->return_statement_for_notfound(); $body .= " $notfound\n" if $notfound; $body .= "}\n"; return (@subs, $body); } 1; __END__ =back =head1 BUGS Not everything is documented yet. Probably others. =head1 AUTHOR Nicholas Clark <nick@ccl4.org> based on the code in C<h2xs> by Larry Wall and others Back

Edit File : Base.pm | Size : 32.53 KB

package ExtUtils::Constant::Base;

use strict;
use vars qw($VERSION);
use Carp;
use Text::Wrap;
use ExtUtils::Constant::Utils qw(C_stringify perl_stringify);
$VERSION = '0.05';

use constant is_perl56 => ($] < 5.007 && $] > 5.005_50);

=head1 NAME

ExtUtils::Constant::Base - base class for ExtUtils::Constant objects

=head1 SYNOPSIS

require ExtUtils::Constant::Base;
    @ISA = 'ExtUtils::Constant::Base';

=head1 DESCRIPTION

ExtUtils::Constant::Base provides a base implementation of methods to
generate C code to give fast constant value lookup by named string. Currently
it's mostly used ExtUtils::Constant::XS, which generates the lookup code
for the constant() subroutine found in many XS modules.

=head1 USAGE

ExtUtils::Constant::Base exports no subroutines. The following methods are
available

=over 4

=cut

sub valid_type {
  # Default to assuming that you don't need different types of return data.
  1;
}
sub default_type {
  '';
}

=item header

A method returning a scalar containing definitions needed, typically for a
C header file.

=cut

sub header {
  ''
}

# This might actually be a return statement. Note that you are responsible
# for any space you might need before your value, as it lets to perform
# "tricks" such as "return KEY_" and have strings appended.
sub assignment_clause_for_type;
# In which case this might be an empty string
sub return_statement_for_type {undef};
sub return_statement_for_notdef;
sub return_statement_for_notfound;

# "#if 1" is true to a C pre-processor
sub macro_from_name {
  1;
}

sub macro_from_item {
  1;
}

sub macro_to_ifdef {
    my ($self, $macro) = @_;
    if (ref $macro) {
	return $macro->[0];
    }
    if (defined $macro && $macro ne "" && $macro ne "1") {
	return $macro ? "#ifdef $macro\n" : "#if 0\n";
    }
    return "";
}

sub macro_to_ifndef {
    my ($self, $macro) = @_;
    if (ref $macro) {
	# Can't invert these stylishly, so "bodge it"
	return "$macro->[0]#else\n";
    }
    if (defined $macro && $macro ne "" && $macro ne "1") {
	return $macro ? "#ifndef $macro\n" : "#if 1\n";
    }
    croak "Can't generate an ifndef for unconditional code";
}

sub macro_to_endif {
    my ($self, $macro) = @_;

if (ref $macro) {
	return $macro->[1];
    }
    if (defined $macro && $macro ne "" && $macro ne "1") {
	return "#endif\n";
    }
    return "";
}

sub name_param {
  'name';
}

# This is possibly buggy, in that it's not mandatory (below, in the main
# C_constant parameters, but is expected to exist here, if it's needed)
# Buggy because if you're definitely pure 8 bit only, and will never be
# presented with your constants in utf8, the default form of C_constant can't
# be told not to do the utf8 version.

sub is_utf8_param {
  'utf8';
}

sub memEQ {
  "!memcmp";
}

=item memEQ_clause args_hashref

A method to return a suitable C C<if> statement to check whether I<name>
is equal to the C variable C<name>. If I<checked_at> is defined, then it
is used to avoid C<memEQ> for short names, or to generate a comment to
highlight the position of the character in the C<switch> statement.

If i<checked_at> is a reference to a scalar, then instead it gives
the characters pre-checked at the beginning, (and the number of chars by
which the C variable name has been advanced. These need to be chopped from
the front of I<name>).

=cut

sub memEQ_clause {
#    if (memEQ(name, "thingy", 6)) {
  # Which could actually be a character comparison or even ""
  my ($self, $args) = @_;
  my ($name, $checked_at, $indent) = @{$args}{qw(name checked_at indent)};
  $indent = ' ' x ($indent || 4);
  my $front_chop;
  if (ref $checked_at) {
    # regexp won't work on 5.6.1 without use utf8; in turn that won't work
    # on 5.005_03.
    substr ($name, 0, length $$checked_at,) = '';
    $front_chop = C_stringify ($$checked_at);
    undef $checked_at;
  }
  my $len = length $name;

if ($len < 2) {
    return $indent . "{\n"
	if (defined $checked_at and $checked_at == 0) or $len == 0;
    # We didn't switch, drop through to the code for the 2 character string
    $checked_at = 1;
  }

my $name_param = $self->name_param;

if ($len < 3 and defined $checked_at) {
    my $check;
    if ($checked_at == 1) {
      $check = 0;
    } elsif ($checked_at == 0) {
      $check = 1;
    }
    if (defined $check) {
      my $char = C_stringify (substr $name, $check, 1);
      # Placate 5.005 with a break in the string. I can't see a good way of
      # getting it to not take [ as introducing an array lookup, even with
      # ${name_param}[$check]
      return $indent . "if ($name_param" . "[$check] == '$char') {\n";
    }
  }
  if (($len == 2 and !defined $checked_at)
     or ($len == 3 and defined ($checked_at) and $checked_at == 2)) {
    my $char1 = C_stringify (substr $name, 0, 1);
    my $char2 = C_stringify (substr $name, 1, 1);
    return $indent .
      "if ($name_param" . "[0] == '$char1' && $name_param" . "[1] == '$char2') {\n";
  }
  if (($len == 3 and defined ($checked_at) and $checked_at == 1)) {
    my $char1 = C_stringify (substr $name, 0, 1);
    my $char2 = C_stringify (substr $name, 2, 1);
    return $indent .
      "if ($name_param" . "[0] == '$char1' && $name_param" . "[2] == '$char2') {\n";
  }

my $pointer = '^';
  my $have_checked_last = defined ($checked_at) && $len == $checked_at + 1;
  if ($have_checked_last) {
    # Checked at the last character, so no need to memEQ it.
    $pointer = C_stringify (chop $name);
    $len--;
  }

$name = C_stringify ($name);
  my $memEQ = $self->memEQ();
  my $body = $indent . "if ($memEQ($name_param, \"$name\", $len)) {\n";
  # Put a little ^ under the letter we checked at
  # Screws up for non printable and non-7 bit stuff, but that's too hard to
  # get right.
  if (defined $checked_at) {
    $body .= $indent . "/*      " . (' ' x length $memEQ)
      . (' ' x length $name_param)
      . (' ' x $checked_at) . $pointer
      . (' ' x ($len - $checked_at + length $len)) . "    */\n";
  } elsif (defined $front_chop) {
    $body .= $indent . "/*                $front_chop"
      . (' ' x ($len + 1 + length $len)) . "    */\n";
  }
  return $body;
}

=item dump_names arg_hashref, ITEM...

An internal function to generate the embedded perl code that will regenerate
the constant subroutines.  I<default_type>, I<types> and I<ITEM>s are the
same as for C_constant.  I<indent> is treated as number of spaces to indent
by.  If C<declare_types> is true a C<$types> is always declared in the perl
code generated, if defined and false never declared, and if undefined C<$types>
is only declared if the values in I<types> as passed in cannot be inferred from
I<default_types> and the I<ITEM>s.

=cut

sub dump_names {
  my ($self, $args, @items) = @_;
  my ($default_type, $what, $indent, $declare_types)
    = @{$args}{qw(default_type what indent declare_types)};
  $indent = ' ' x ($indent || 0);

my $result;
  my (@simple, @complex, %used_types);
  foreach (@items) {
    my $type;
    if (ref $_) {
      $type = $_->{type} || $default_type;
      if ($_->{utf8}) {
        # For simplicity always skip the bytes case, and reconstitute this entry
        # from its utf8 twin.
        next if $_->{utf8} eq 'no';
        # Copy the hashref, as we don't want to mess with the caller's hashref.
        $_ = {%$_};
        unless (is_perl56) {
          utf8::decode ($_->{name});
        } else {
          $_->{name} = pack 'U*', unpack 'U0U*', $_->{name};
        }
        delete $_->{utf8};
      }
    } else {
      $_ = {name=>$_};
      $type = $default_type;
    }
    $used_types{$type}++;
    if ($type eq $default_type
        # grr 5.6.1
        and length $_->{name}
        and length $_->{name} == ($_->{name} =~ tr/A-Za-z0-9_//)
        and !defined ($_->{macro}) and !defined ($_->{value})
        and !defined ($_->{default}) and !defined ($_->{pre})
        and !defined ($_->{post}) and !defined ($_->{def_pre})
        and !defined ($_->{def_post}) and !defined ($_->{weight})) {
      # It's the default type, and the name consists only of A-Za-z0-9_
      push @simple, $_->{name};
    } else {
      push @complex, $_;
    }
  }

if (!defined $declare_types) {
    # Do they pass in any types we weren't already using?
    foreach (keys %$what) {
      next if $used_types{$_};
      $declare_types++; # Found one in $what that wasn't used.
      last; # And one is enough to terminate this loop
    }
  }
  if ($declare_types) {
    $result = $indent . 'my $types = {map {($_, 1)} qw('
      . join (" ", sort keys %$what) . ")};\n";
  }
  local $Text::Wrap::huge = 'overflow';
  local $Text::Wrap::columns = 80;
  $result .= wrap ($indent . "my \@names = (qw(",
		   $indent . "               ", join (" ", sort @simple) . ")");
  if (@complex) {
    foreach my $item (sort {$a->{name} cmp $b->{name}} @complex) {
      my $name = perl_stringify $item->{name};
      my $line = ",\n$indent            {name=>\"$name\"";
      $line .= ", type=>\"$item->{type}\"" if defined $item->{type};
      foreach my $thing (qw (macro value default pre post def_pre def_post)) {
        my $value = $item->{$thing};
        if (defined $value) {
          if (ref $value) {
            $line .= ", $thing=>[\""
              . join ('", "', map {perl_stringify $_} @$value) . '"]';
          } else {
            $line .= ", $thing=>\"" . perl_stringify($value) . "\"";
          }
        }
      }
      $line .= "}";
      # Ensure that the enclosing C comment doesn't end
      # by turning */  into *" . "/
      $line =~ s!\*\/!\*" . "/!gs;
      # gcc -Wall doesn't like finding /* inside a comment
      $line =~ s!\/\*!/" . "\*!gs;
      $result .= $line;
    }
  }
  $result .= ");\n";

$result;
}

=item assign arg_hashref, VALUE...

A method to return a suitable assignment clause. If I<type> is aggregate
(eg I<PVN> expects both pointer and length) then there should be multiple
I<VALUE>s for the components. I<pre> and I<post> if defined give snippets
of C code to proceed and follow the assignment. I<pre> will be at the start
of a block, so variables may be defined in it.

=cut
# Hmm. value undef to to NOTDEF? value () to do NOTFOUND?

sub assign {
  my $self = shift;
  my $args = shift;
  my ($indent, $type, $pre, $post, $item)
      = @{$args}{qw(indent type pre post item)};
  $post ||= '';
  my $clause;
  my $close;
  if ($pre) {
    chomp $pre;
    $close = "$indent}\n";
    $clause = $indent . "{\n";
    $indent .= "  ";
    $clause .= "$indent$pre";
    $clause .= ";" unless $pre =~ /;$/;
    $clause .= "\n";
  }
  confess "undef \$type" unless defined $type;
  confess "Can't generate code for type $type"
    unless $self->valid_type($type);

$clause .= join '', map {"$indent$_\n"}
    $self->assignment_clause_for_type({type=>$type,item=>$item}, @_);
  chomp $post;
  if (length $post) {
    $clause .= "$post";
    $clause .= ";" unless $post =~ /;$/;
    $clause .= "\n";
  }
  my $return = $self->return_statement_for_type($type);
  $clause .= "$indent$return\n" if defined $return;
  $clause .= $close if $close;
  return $clause;
}

=item return_clause arg_hashref, ITEM

A method to return a suitable C<#ifdef> clause. I<ITEM> is a hashref
(as passed to C<C_constant> and C<match_clause>. I<indent> is the number
of spaces to indent, defaulting to 6.

=cut

sub return_clause {

##ifdef thingy
#      *iv_return = thingy;
#      return PERL_constant_ISIV;
##else
#      return PERL_constant_NOTDEF;
##endif
  my ($self, $args, $item) = @_;
  my $indent = $args->{indent};

my ($name, $value, $default, $pre, $post, $def_pre, $def_post, $type)
    = @$item{qw (name value default pre post def_pre def_post type)};
  $value = $name unless defined $value;
  my $macro = $self->macro_from_item($item);
  $indent = ' ' x ($indent || 6);
  unless (defined $type) {
    # use Data::Dumper; print STDERR Dumper ($item);
    confess "undef \$type";
  }

##ifdef thingy
  my $clause = $self->macro_to_ifdef($macro);

#      *iv_return = thingy;
  #      return PERL_constant_ISIV;
  $clause
    .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre, post=>$post,
		       item=>$item}, ref $value ? @$value : $value);

if (defined $macro && $macro ne "" && $macro ne "1") {
    ##else
    $clause .= "#else\n";

#      return PERL_constant_NOTDEF;
    if (!defined $default) {
      my $notdef = $self->return_statement_for_notdef();
      $clause .= "$indent$notdef\n" if defined $notdef;
    } else {
      my @default = ref $default ? @$default : $default;
      $type = shift @default;
      $clause .= $self->assign ({indent=>$indent, type=>$type, pre=>$pre,
				 post=>$post, item=>$item}, @default);
    }
  }
  ##endif
  $clause .= $self->macro_to_endif($macro);

return $clause;
}

sub match_clause {
  # $offset defined if we have checked an offset.
  my ($self, $args, $item) = @_;
  my ($offset, $indent) = @{$args}{qw(checked_at indent)};
  $indent = ' ' x ($indent || 4);
  my $body = '';
  my ($no, $yes, $either, $name, $inner_indent);
  if (ref $item eq 'ARRAY') {
    ($yes, $no) = @$item;
    $either = $yes || $no;
    confess "$item is $either expecting hashref in [0] || [1]"
      unless ref $either eq 'HASH';
    $name = $either->{name};
  } else {
    confess "$item->{name} has utf8 flag '$item->{utf8}', should be false"
      if $item->{utf8};
    $name = $item->{name};
    $inner_indent = $indent;
  }

$body .= $self->memEQ_clause ({name => $name, checked_at => $offset,
				 indent => length $indent});
  # If we've been presented with an arrayref for $item, then the user string
  # contains in the range 128-255, and we need to check whether it was utf8
  # (or not).
  # In the worst case we have two named constants, where one's name happens
  # encoded in UTF8 happens to be the same byte sequence as the second's
  # encoded in (say) ISO-8859-1.
  # In this case, $yes and $no both have item hashrefs.
  if ($yes) {
    $body .= $indent . "  if (" . $self->is_utf8_param . ") {\n";
  } elsif ($no) {
    $body .= $indent . "  if (!" . $self->is_utf8_param . ") {\n";
  }
  if ($either) {
    $body .= $self->return_clause ({indent=>4 + length $indent}, $either);
    if ($yes and $no) {
      $body .= $indent . "  } else {\n";
      $body .= $self->return_clause ({indent=>4 + length $indent}, $no);
    }
    $body .= $indent . "  }\n";
  } else {
    $body .= $self->return_clause ({indent=>2 + length $indent}, $item);
  }
  $body .= $indent . "}\n";
}

=item switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM...

An internal method to generate a suitable C<switch> clause, called by
C<C_constant> I<ITEM>s are in the hash ref format as given in the description
of C<C_constant>, and must all have the names of the same length, given by
I<NAMELEN>.  I<ITEMHASH> is a reference to a hash, keyed by name, values being
the hashrefs in the I<ITEM> list.  (No parameters are modified, and there can
be keys in the I<ITEMHASH> that are not in the list of I<ITEM>s without
causing problems - the hash is passed in to save generating it afresh for
each call).

=cut

sub switch_clause {
  my ($self, $args, $namelen, $items, @items) = @_;
  my ($indent, $comment) = @{$args}{qw(indent comment)};
  $indent = ' ' x ($indent || 2);

local $Text::Wrap::huge = 'overflow';
  local $Text::Wrap::columns = 80;

my @names = sort map {$_->{name}} @items;
  my $leader = $indent . '/* ';
  my $follower = ' ' x length $leader;
  my $body = $indent . "/* Names all of length $namelen.  */\n";
  if (defined $comment) {
    $body = wrap ($leader, $follower, $comment) . "\n";
    $leader = $follower;
  }
  my @safe_names = @names;
  foreach (@safe_names) {
    confess sprintf "Name '$_' is length %d, not $namelen", length
      unless length == $namelen;
    # Argh. 5.6.1
    # next unless tr/A-Za-z0-9_//c;
    next if tr/A-Za-z0-9_// == length;
    $_ = '"' . perl_stringify ($_) . '"';
    # Ensure that the enclosing C comment doesn't end
    # by turning */  into *" . "/
    s!\*\/!\*"."/!gs;
    # gcc -Wall doesn't like finding /* inside a comment
    s!\/\*!/"."\*!gs;
  }
  $body .= wrap ($leader, $follower, join (" ", @safe_names) . " */") . "\n";
  # Figure out what to switch on.
  # (RMS, Spread of jump table, Position, Hashref)
  my @best = (1e38, ~0);
  # Prefer the last character over the others. (As it lets us shorten the
  # memEQ clause at no cost).
  foreach my $i ($namelen - 1, 0 .. ($namelen - 2)) {
    my ($min, $max) = (~0, 0);
    my %spread;
    if (is_perl56) {
      # Need proper Unicode preserving hash keys for bytes in range 128-255
      # here too, for some reason. grr 5.6.1 yet again.
      tie %spread, 'ExtUtils::Constant::Aaargh56Hash';
    }
    foreach (@names) {
      my $char = substr $_, $i, 1;
      my $ord = ord $char;
      confess "char $ord is out of range" if $ord > 255;
      $max = $ord if $ord > $max;
      $min = $ord if $ord < $min;
      push @{$spread{$char}}, $_;
      # warn "$_ $char";
    }
    # I'm going to pick the character to split on that minimises the root
    # mean square of the number of names in each case. Normally this should
    # be the one with the most keys, but it may pick a 7 where the 8 has
    # one long linear search. I'm not sure if RMS or just sum of squares is
    # actually better.
    # $max and $min are for the tie-breaker if the root mean squares match.
    # Assuming that the compiler may be building a jump table for the
    # switch() then try to minimise the size of that jump table.
    # Finally use < not <= so that if it still ties the earliest part of
    # the string wins. Because if that passes but the memEQ fails, it may
    # only need the start of the string to bin the choice.
    # I think. But I'm micro-optimising. :-)
    # OK. Trump that. Now favour the last character of the string, before the
    # rest.
    my $ss;
    $ss += @$_ * @$_ foreach values %spread;
    my $rms = sqrt ($ss / keys %spread);
    if ($rms < $best[0] || ($rms == $best[0] && ($max - $min) < $best[1])) {
      @best = ($rms, $max - $min, $i, \%spread);
    }
  }
  confess "Internal error. Failed to pick a switch point for @names"
    unless defined $best[2];
  # use Data::Dumper; print Dumper (@best);
  my ($offset, $best) = @best[2,3];
  $body .= $indent . "/* Offset $offset gives the best switch position.  */\n";

my $do_front_chop = $offset == 0 && $namelen > 2;
  if ($do_front_chop) {
    $body .= $indent . "switch (*" . $self->name_param() . "++) {\n";
  } else {
    $body .= $indent . "switch (" . $self->name_param() . "[$offset]) {\n";
  }
  foreach my $char (sort keys %$best) {
    confess sprintf "'$char' is %d bytes long, not 1", length $char
      if length ($char) != 1;
    confess sprintf "char %#X is out of range", ord $char if ord ($char) > 255;
    $body .= $indent . "case '" . C_stringify ($char) . "':\n";
    foreach my $thisone (sort {
	# Deal with the case of an item actually being an array ref to 1 or 2
	# hashrefs. Don't assign to $a or $b, as they're aliases to the orignal
	my $l = ref $a eq 'ARRAY' ? ($a->[0] || $->[1]) : $a;
	my $r = ref $b eq 'ARRAY' ? ($b->[0] || $->[1]) : $b;
	# Sort by weight first
	($r->{weight} || 0) <=> ($l->{weight} || 0)
	    # Sort equal weights by name
	    or $l->{name} cmp $r->{name}}
			 # If this looks evil, maybe it is.  $items is a
			 # hashref, and we're doing a hash slice on it
			 @{$items}{@{$best->{$char}}}) {
      # warn "You are here";
      if ($do_front_chop) {
        $body .= $self->match_clause ({indent => 2 + length $indent,
				       checked_at => \$char}, $thisone);
      } else {
        $body .= $self->match_clause ({indent => 2 + length $indent,
				       checked_at => $offset}, $thisone);
      }
    }
    $body .= $indent . "  break;\n";
  }
  $body .= $indent . "}\n";
  return $body;
}

sub C_constant_return_type {
  "static int";
}

sub C_constant_prefix_param {
  '';
}

sub C_constant_prefix_param_defintion {
  '';
}

sub name_param_definition {
  "const char *" . $_[0]->name_param;
}

sub namelen_param {
  'len';
}

sub namelen_param_definition {
  'size_t ' . $_[0]->namelen_param;
}

sub C_constant_other_params {
  '';
}

sub C_constant_other_params_defintion {
  '';
}

=item params WHAT

An "internal" method, subject to change, currently called to allow an
overriding class to cache information that will then be passed into all
the C<*param*> calls. (Yes, having to read the source to make sense of this is
considered a known bug). I<WHAT> is be a hashref of types the constant
function will return. In ExtUtils::Constant::XS this method is used to
returns a hashref keyed IV NV PV SV to show which combination of pointers will
be needed in the C argument list generated by
C_constant_other_params_definition and C_constant_other_params

=cut

sub params {
  '';
}

=item dogfood arg_hashref, ITEM...

An internal function to generate the embedded perl code that will regenerate
the constant subroutines.  Parameters are the same as for C_constant.

Currently the base class does nothing and returns an empty string.

=cut

sub dogfood {
  ''
}

=item normalise_items args, default_type, seen_types, seen_items, ITEM...

Convert the items to a normalised form. For 8 bit and Unicode values converts
the item to an array of 1 or 2 items, both 8 bit and UTF-8 encoded.

=cut

sub normalise_items
{
    my $self = shift;
    my $args = shift;
    my $default_type = shift;
    my $what = shift;
    my $items = shift;
    my @new_items;
    foreach my $orig (@_) {
	my ($name, $item);
      if (ref $orig) {
        # Make a copy which is a normalised version of the ref passed in.
        $name = $orig->{name};
        my ($type, $macro, $value) = @$orig{qw (type macro value)};
        $type ||= $default_type;
        $what->{$type} = 1;
        $item = {name=>$name, type=>$type};

undef $macro if defined $macro and $macro eq $name;
        $item->{macro} = $macro if defined $macro;
        undef $value if defined $value and $value eq $name;
        $item->{value} = $value if defined $value;
        foreach my $key (qw(default pre post def_pre def_post weight
			    not_constant)) {
          my $value = $orig->{$key};
          $item->{$key} = $value if defined $value;
          # warn "$key $value";
        }
      } else {
        $name = $orig;
        $item = {name=>$name, type=>$default_type};
        $what->{$default_type} = 1;
      }
      warn +(ref ($self) || $self)
	. "doesn't know how to handle values of type $_ used in macro $name"
	  unless $self->valid_type ($item->{type});
      # tr///c is broken on 5.6.1 for utf8, so my original tr/\0-\177//c
      # doesn't work. Upgrade to 5.8
      # if ($name !~ tr/\0-\177//c || $] < 5.005_50) {
      if ($name =~ tr/\0-\177// == length $name || $] < 5.005_50
	 || $args->{disable_utf8_duplication}) {
        # No characters outside 7 bit ASCII.
        if (exists $items->{$name}) {
          die "Multiple definitions for macro $name";
        }
        $items->{$name} = $item;
      } else {
        # No characters outside 8 bit. This is hardest.
        if (exists $items->{$name} and ref $items->{$name} ne 'ARRAY') {
          confess "Unexpected ASCII definition for macro $name";
        }
        # Again, 5.6.1 tr broken, so s/5\.6.*/5\.8\.0/;
        # if ($name !~ tr/\0-\377//c) {
        if ($name =~ tr/\0-\377// == length $name) {
#          if ($] < 5.007) {
#            $name = pack "C*", unpack "U*", $name;
#          }
          $item->{utf8} = 'no';
          $items->{$name}[1] = $item;
          push @new_items, $item;
          # Copy item, to create the utf8 variant.
          $item = {%$item};
        }
        # Encode the name as utf8 bytes.
        unless (is_perl56) {
          utf8::encode($name);
        } else {
#          warn "Was >$name< " . length ${name};
          $name = pack 'C*', unpack 'C*', $name . pack 'U*';
#          warn "Now '${name}' " . length ${name};
        }
        if ($items->{$name}[0]) {
          die "Multiple definitions for macro $name";
        }
        $item->{utf8} = 'yes';
        $item->{name} = $name;
        $items->{$name}[0] = $item;
        # We have need for the utf8 flag.
        $what->{''} = 1;
      }
      push @new_items, $item;
    }
    @new_items;
}

=item C_constant arg_hashref, ITEM...

A function that returns a B<list> of C subroutine definitions that return
the value and type of constants when passed the name by the XS wrapper.
I<ITEM...> gives a list of constant names. Each can either be a string,
which is taken as a C macro name, or a reference to a hash with the following
keys

=over 8

=item name

The name of the constant, as seen by the perl code.

=item type

The type of the constant (I<IV>, I<NV> etc)

=item value

A C expression for the value of the constant, or a list of C expressions if
the type is aggregate. This defaults to the I<name> if not given.

=item macro

The C pre-processor macro to use in the C<#ifdef>. This defaults to the
I<name>, and is mainly used if I<value> is an C<enum>. If a reference an
array is passed then the first element is used in place of the C<#ifdef>
line, and the second element in place of the C<#endif>. This allows
pre-processor constructions such as

#if defined (foo)
    #if !defined (bar)
    ...
    #endif
    #endif

to be used to determine if a constant is to be defined.

A "macro" 1 signals that the constant is always defined, so the C<#if>/C<#endif>
test is omitted.

=item default

Default value to use (instead of C<croak>ing with "your vendor has not
defined...") to return if the macro isn't defined. Specify a reference to
an array with type followed by value(s).

=item pre

C code to use before the assignment of the value of the constant. This allows
you to use temporary variables to extract a value from part of a C<struct>
and return this as I<value>. This C code is places at the start of a block,
so you can declare variables in it.

=item post

C code to place between the assignment of value (to a temporary) and the
return from the function. This allows you to clear up anything in I<pre>.
Rarely needed.

=item def_pre

=item def_post

Equivalents of I<pre> and I<post> for the default value.

=item utf8

Generated internally. Is zero or undefined if name is 7 bit ASCII,
"no" if the name is 8 bit (and so should only match if SvUTF8() is false),
"yes" if the name is utf8 encoded.

The internals automatically clone any name with characters 128-255 but none
256+ (ie one that could be either in bytes or utf8) into a second entry
which is utf8 encoded.

=item weight

Optional sorting weight for names, to determine the order of
linear testing when multiple names fall in the same case of a switch clause.
Higher comes earlier, undefined defaults to zero.

=back

In the argument hashref, I<package> is the name of the package, and is only
used in comments inside the generated C code. I<subname> defaults to
C<constant> if undefined.

I<default_type> is the type returned by C<ITEM>s that don't specify their
type. It defaults to the value of C<default_type()>. I<types> should be given
either as a comma separated list of types that the C subroutine I<subname>
will generate or as a reference to a hash. I<default_type> will be added to
the list if not present, as will any types given in the list of I<ITEM>s. The
resultant list should be the same list of types that C<XS_constant> is
given. [Otherwise C<XS_constant> and C<C_constant> may differ in the number of
parameters to the constant function. I<indent> is currently unused and
ignored. In future it may be used to pass in information used to change the C
indentation style used.]  The best way to maintain consistency is to pass in a
hash reference and let this function update it.

I<breakout> governs when child functions of I<subname> are generated.  If there
are I<breakout> or more I<ITEM>s with the same length of name, then the code
to switch between them is placed into a function named I<subname>_I<len>, for
example C<constant_5> for names 5 characters long.  The default I<breakout> is
3.  A single C<ITEM> is always inlined.

=cut

# The parameter now BREAKOUT was previously documented as:
#
# I<NAMELEN> if defined signals that all the I<name>s of the I<ITEM>s are of
# this length, and that the constant name passed in by perl is checked and
# also of this length. It is used during recursion, and should be C<undef>
# unless the caller has checked all the lengths during code generation, and
# the generated subroutine is only to be called with a name of this length.
#
# As you can see it now performs this function during recursion by being a
# scalar reference.

sub C_constant {
  my ($self, $args, @items) = @_;
  my ($package, $subname, $default_type, $what, $indent, $breakout) =
    @{$args}{qw(package subname default_type types indent breakout)};
  $package ||= 'Foo';
  $subname ||= 'constant';
  # I'm not using this. But a hashref could be used for full formatting without
  # breaking this API
  # $indent ||= 0;

my ($namelen, $items);
  if (ref $breakout) {
    # We are called recursively. We trust @items to be normalised, $what to
    # be a hashref, and pinch %$items from our parent to save recalculation.
    ($namelen, $items) = @$breakout;
  } else {
    $items = {};
    if (is_perl56) {
      # Need proper Unicode preserving hash keys.
      require ExtUtils::Constant::Aaargh56Hash;
      tie %$items, 'ExtUtils::Constant::Aaargh56Hash';
    }
    $breakout ||= 3;
    $default_type ||= $self->default_type();
    if (!ref $what) {
      # Convert line of the form IV,UV,NV to hash
      $what = {map {$_ => 1} split /,\s*/, ($what || '')};
      # Figure out what types we're dealing with, and assign all unknowns to the
      # default type
    }
    @items = $self->normalise_items ({}, $default_type, $what, $items, @items);
    # use Data::Dumper; print Dumper @items;
  }
  my $params = $self->params ($what);

# Probably "static int"
  my ($body, @subs);
  $body = $self->C_constant_return_type($params) . "\n$subname ("
    # Eg "pTHX_ "
    . $self->C_constant_prefix_param_defintion($params)
      # Probably "const char *name"
      . $self->name_param_definition($params);
  # Something like ", STRLEN len"
  $body .= ", " . $self->namelen_param_definition($params)
    unless defined $namelen;
  $body .= $self->C_constant_other_params_defintion($params);
  $body .= ") {\n";

if (defined $namelen) {
    # We are a child subroutine. Print the simple description
    my $comment = 'When generated this function returned values for the list'
      . ' of names given here.  However, subsequent manual editing may have'
        . ' added or removed some.';
    $body .= $self->switch_clause ({indent=>2, comment=>$comment},
				   $namelen, $items, @items);
  } else {
    # We are the top level.
    $body .= "  /* Initially switch on the length of the name.  */\n";
    $body .= $self->dogfood ({package => $package, subname => $subname,
			      default_type => $default_type, what => $what,
			      indent => $indent, breakout => $breakout},
			     @items);
    $body .= '  switch ('.$self->namelen_param().") {\n";
    # Need to group names of the same length
    my @by_length;
    foreach (@items) {
      push @{$by_length[length $_->{name}]}, $_;
    }
    foreach my $i (0 .. $#by_length) {
      next unless $by_length[$i];	# None of this length
      $body .= "  case $i:\n";
      if (@{$by_length[$i]} == 1) {
        my $only_thing = $by_length[$i]->[0];
        if ($only_thing->{utf8}) {
          if ($only_thing->{utf8} eq 'yes') {
            # With utf8 on flag item is passed in element 0
            $body .= $self->match_clause (undef, [$only_thing]);
          } else {
            # With utf8 off flag item is passed in element 1
            $body .= $self->match_clause (undef, [undef, $only_thing]);
          }
        } else {
          $body .= $self->match_clause (undef, $only_thing);
        }
      } elsif (@{$by_length[$i]} < $breakout) {
        $body .= $self->switch_clause ({indent=>4},
				       $i, $items, @{$by_length[$i]});
      } else {
        # Only use the minimal set of parameters actually needed by the types
        # of the names of this length.
        my $what = {};
        foreach (@{$by_length[$i]}) {
          $what->{$_->{type}} = 1;
          $what->{''} = 1 if $_->{utf8};
        }
        $params = $self->params ($what);
        push @subs, $self->C_constant ({package=>$package,
					subname=>"${subname}_$i",
					default_type => $default_type,
					types => $what, indent => $indent,
					breakout => [$i, $items]},
				       @{$by_length[$i]});
        $body .= "    return ${subname}_$i ("
	  # Eg "aTHX_ "
	  . $self->C_constant_prefix_param($params)
	    # Probably "name"
	    . $self->name_param($params);
	$body .= $self->C_constant_other_params($params);
        $body .= ");\n";
      }
      $body .= "    break;\n";
    }
    $body .= "  }\n";
  }
  my $notfound = $self->return_statement_for_notfound();
  $body .= "  $notfound\n" if $notfound;
  $body .= "}\n";
  return (@subs, $body);
}

1;
__END__

=back

=head1 BUGS

Not everything is documented yet.

Probably others.

=head1 AUTHOR

Nicholas Clark <nick@ccl4.org> based on the code in C<h2xs> by Larry Wall and
others

Back