scripts/options.awk - third_party/libpng - Git at Google

 #!/bin/awk -f
 # scripts/options.awk - library build configuration control
 #
 # last changed in libpng version 1.5.0 - April 27, 2010
 #
 # Copyright (c) 1998-2010 Glenn Randers-Pehrson
 #
 # This code is released under the libpng license.
 # For conditions of distribution and use, see the disclaimer
 # and license in png.h

 # The output of this script is written to the file given by
 # the variable 'out'.  The script is run twice, once with
 # an intermediate output file, 'options.tmp' then again on
 # that file to produce the final output.  Each time the
 # output files and whether or not to pre-prrocess must be
 # specified:
 #
 #  awk -f scripts/options.awk pre=1 out=options.tmp scripts/options.dat 1>&2
 #  awk -f scripts/options.awk pre=0 out=options.dfn options.tmp 1>&2

 BEGIN{
     out="/dev/null"                      # intermediate, preprocessed, file
     pre=-1                               # preprocess
     start="PNG_DEFN_MAGIC-"              # Arbitrary start
     end="-PNG_DEFN_END"                  # Arbitrary end
     cx= "/@@@*"                          # Open C comment for output file
     comment=start cx                     # Comment start
     cend="*/" end                        # Comment end
     def=start "#define PNG_@@@"          # Arbitrary define
     sup="@@@_SUPPORTED" end              # end supported option
     und=comment "#undef PNG_@@@"         # Unsupported option
     une="@@@_SUPPORTED" cend             # end unsupported option
     error=start "ERROR:"                 # error message
     deb=0                                # debug - set on command line
     logunsupported=0                     # write unsupported options too

     # Precreate arrays
     option[""] = ""      # list of all options: default on/off/""
     done[""] = 1         # marks option as having been output
     requires[""] = ""    # requires by option
     iffs[""] = ""        # if by option
     enabledby[""] = ""   # options that enable it by option
     setting[""] = ""     # requires by setting
     defaults[""] = ""    # used for a defaulted value
     doneset[""] = 1      # marks setting as having been output
     r[""] = ""           # Temporary array

     # For decorating the output file
     protect = ""
 }

 # Preprocessing - this just copies the input file with lines
 # that need preprocessing (just chunk at present) expanded
 pre && $1 != "chunk"{
     print >out
     next
 }

 # The first characters of the line determine how it is processed,
 # leading spaces are ignored.  In general tokens that are not
 # keywords are the names of options.  An option 'name' is
 # controlled by the definition of the corresponding macros:
 #
 #   PNG_name_SUPPORTED    The option is turned on
 #   PNG_NO_name
 #   PNG_NO_name_SUPPORTED If the first macro is not defined
 #                         either of these will turn the option off
 #
 # If none of these macros are defined the option is turned on, unless
 # the keyword 'off' is given in a line relating to the option.  The
 # keyword 'on' can also be given, but it will be ignored (since it is
 # the default.)
 #
 # In the syntax below a 'name' is indicated by "NAME", other macro
 # values are indicated by "MACRO", as with "NAME" the leading "PNG_"
 # is omitted, but in this case the "NO_" prefix and the "_SUPPORTED"
 # suffix are never used.
 #
 # Each line is introduced by a keyword - the first non-space characters
 # on the line.  A line starting with a '#' is a comment - it is totally
 # ignored.  Keywords are as follows, a NAME, is simply a macro name
 # without the leading PNG_, PNG_NO_ or the trailing _SUPPORTED.

 $1 ~ /^#/ || $0 ~ /^[ 	]*$/{
     next
 }

 # com <comment>
 #   The whole line is placed in the output file as a comment with
 #   the preceding 'com' removed
 $1 == "com"{
     if (NF > 1) {
 	sub(/^[ 	]*com[ 	]*/, "")
 	print comment, $0, cend >out
     } else
     	print start end >out
     next
 }

 # file output input protect
 #   Informational: the official name of the input file (without
 #   make generated local directories), the official name of the
 #   output file and, if required, a name to use in a protection
 #   macro for the contents.
 $1 == "file" && NF >= 2{
     print comment, $2, cend >out
     print comment, "Machine generated file: DO NOT EDIT", cend >out
     if (NF >= 3)
     	print comment, "Derived from:", $3, cend >out
     protect = $4
     if (protect != "") {
     	print start "#ifndef", protect end >out
     	print start "#define", protect end >out
     }
     next
 }

 # option NAME ( (requires|enables|if) NAME* | on | off )*
 #   Declares an option 'NAME' and describes its default setting (on|off)
 #   and its relationship to other options.  The option is disabled
 #   unless *all* the options listed after 'requires' are set and at
 #   least one of the options listed after 'if' is set.  If the
 #   option is set then it turns on all the options listed after 'enables'.

 $1 == "option" && NF >= 2{
     onoff = option[$2]  # records default on or default off
     key = ""
     for (i=3; i<=NF; ++i) {
     	if ($(i) == "on" || $(i) == "off") {
 	    key = ""
 	    if (onoff != $(i)) {
 	    	if (onoff == "")
 		    onoff = $(i)
 		else {
 		    # Print a message, otherwise the error
 		    # below is incomprehensible
 		    print $2 ": currently", onoff ": attempt to turn", $(i)
 		    break
 		}
 	    }
 	} else if ($(i) == "requires" || $(i) == "if" || $(i) == "enables") {
 	    key = $(i)
 	} else if (key == "requires") {
 	    requires[$2] = requires[$2] " " $(i)
 	} else if (key == "if") {
 	    iffs[$2] = iffs[$2] " " $(i)
 	} else if (key == "enables") {
 	    enabledby[$(i)] = enabledby[$(i)] " " $2
 	} else
 	    break # bad line format
     }

     if (i > NF) {
 	# Set the option - this may explicitly set it to "", that's good
 	# becaue we need to ensure it exists and we can't rely on some
 	# actually quite sensible awk implementation not optimising the
 	# read above away (gawk doesn't)
 	option[$2] = onoff
 	next
     }
     # Else fall through to the error handler
 }

 # chunk NAME [requires OPT] [off]
 #   Expands to the 'option' settings appropriate to the reading and
 #   writing of an ancilliary PNG chunk 'NAME':
 #
 #    option READ_NAME requires READ_ANCILLARY_CHUNKS [READ_OPT]
 #    option READ_NAME enables NAME
 #    [option READ_NAME off]
 #    option WRITE_NAME requires WRITE_ANCILLARY_CHUNKS [WRITE_OPT]
 #    option WRITE_NAME enables NAME
 #    [option WRITE_NAME off]

 pre && $1 == "chunk" && NF >= 2{
     # 'chunk' is handled on the first pass by writing appropriate
     # 'option' lines into the intermediate file.
     onoff = ""
     reqread = ""
     reqwrite = ""
     i = 3 # indicates format error
     if (NF > 2) {
 	# read the keywords/additional OPTS
     	req = 0
 	for (i=3; i<=NF; ++i) {
 	    if ($(i) == "on" || $(i) == "off") {
 	    	if (onoff != $(i)) {
 		    if (onoff == "")
 			onoff = $(i)
 		    else
 		    	break # on/off conflict
 		}
 	    } else if ($(i) == "requires")
 	    	req = 1
 	    else if (req != 1)
 	    	break # bad line: handled below
 	    else {
 	    	reqread = reqread " READ_" $(i)
 	    	reqwrite = reqwrite " WRITE_" $(i)
 	    }
 	}
     }

     if (i > NF) {
     	# Output new 'option' lines to the intermediate file (out)
 	print "option READ_" $2,
 		"requires READ_ANCILLARY_CHUNKS" reqread,
 		"enables", $2, onoff >out
     	print "option WRITE_" $2,
 		"requires WRITE_ANCILLARY_CHUNKS" reqwrite,
 		"enables", $2, onoff >out
 	next
     }
     # Else hit the error handler below - bad line format!
 }

 # setting MACRO ( requires MACRO* )* [ default VALUE ]
 #    Behaves in a similar way to 'option' without looking for NO_ or
 #    _SUPPORTED; the macro is enabled if it is defined so long as all
 #    the 'requires' macros are also defined.  The definitions may be
 #    empty, an error will be issued if the 'requires' macros are
 #    *not* defined.  If given the 'default' value is used if the
 #    macro is not defined.  The default value will be re-tokenised.
 #    (BTW: this is somewhat restrictive, it mainly exists for the
 #    support of non-standard configurations and numeric parameters,
 #    see the uses in scripts/options.dat

 $1 == "setting" && (NF == 2 || NF >= 3 && ($3 == "requires" || $3 == "default")){
     reqs = ""
     deflt = ""
     isdef = 0
     key = ""
     for (i=3; i<=NF; ++i)
     	if ($(i) == "requires" || $(i) == "default") {
 	    key = $(i)
 	    if (key == "default") isdef = 1
 	} else if (key == "requires")
 	    reqs = reqs " " $(i)
 	else if (key == "default")
 	    deflt = deflt " " $(i)
 	else
 	    break # Format error, handled below

     setting[$2] = reqs
     if (isdef && deflt == "")
     	deflt = " " # as a flag to force output
     defaults[$2] = deflt
     next
 }

 # The order of the dependency lines (option, chunk, setting) is irrelevant
 # - the 'enables', 'requires' and 'if' settings will be used to determine
 # the correct order in the output and the final values in pnglibconf.h are
 # not order dependent.  'requires' and 'if' entries take precedence over
 # 'enables' from other options; if an option requires another option it
 # won't be set regardless of any options that enable it unless the other
 # option is also enabled.
 #
 # Similarly 'enables' trumps a NO_ definition in CFLAGS or pngusr.h
 #
 # For simplicity cycles in the definitions are regarded as errors,
 # even if they are not ambiguous.
 # A given NAME can be specified in as many 'option' lines as required, the
 # definitions are additive.

 # For backwards compatibility equivalent macros may be listed thus:
 #
 # = [NO_]NAME MACRO
 #   Makes -DMACRO equivalent to -DPNG_NO_NAME or -DPNG_NAME_SUPPORTED
 #   as appropriate.
 #
 # The definition is injected into the C compiler input when encountered
 # in the second pass (so all these definitions appear *after* the @
 # lines!)
 #
 # 'NAME' is as above, but 'MACRO' is the full text of the equivalent
 # old, deprecated, macro.

 $1 == "=" && NF == 3{
     print "#ifdef PNG_" $3 >out
     if ($2 ~ /^NO_/)
 	print "#   define PNG_" $2 >out
     else
 	print "#   define PNG_" $2 "_SUPPORTED" >out
     print "#endif" >out
     next
 }

 # Lines may be injected into the C compiler input by preceding them
 # with an "@" character.  The line is copied with just the leading
 # @ removed.

 $1 ~ /^@/{
     sub(/^[ 	]*@/, "")
     print >out
     next
 }

 # Check for unreognized lines, because of the preprocessing chunk
 # format errors will be detected on the first pass independent of
 # any other format errors.
 {
     print "options.awk: bad line (" NR "):", $0
     exit 1
 }

 # For checking purposes names that start with "ok_" or "fail_" are
 # not output to pnglibconf.h and must be either enabled or disabled
 # respectively for the build to succeed.  This allows interdependencies
 # between options of the form "at least one of" or "at most one of"
 # to be checked.  For example:
 #
 # option FLOATING_POINT enables ok_math
 # option FIXED_POINT enables ok_math
 #    This ensures that at least one of FLOATING_POINT and FIXED_POINT
 #    must be set for the build to succeed.
 #
 # option fail_math requires FLOATING_POINT FIXED_POINT
 #    This means the build will fail if *both* FLOATING_POINT and
 #    FIXED_POINT are set (this is an example; in fact both are allowed.)
 #
 # If all these options were given the build would require exactly one
 # of the names to be enabled.

 END{
     if (out == "/dev/null") {
 	print "out=output.file must be given on the command line"
 	exit 1
     }
     if (pre) {
     	if (pre != 1) {
 	    print "pre=0 or pre=1 must be given on command line"
 	    exit 1
 	}
 	exit 0
     }

     # Do the 'setting' values first, the algorithm the standard
     # tree walk (O(1)) done in an O(2) while/for loop; interations
     # settings x depth, outputing the deepest required macros
     # first.
     print "" >out
     print "/* SETTINGS */" >out
     print comment, "settings", cend >out
     finished = 0
     while (!finished) {
     	finished = 1
 	movement = 0 # done nothing
 	for (i in setting) if (!doneset[i]) {
 	    nreqs = split(setting[i], r)
 	    if (nreqs > 0) {
 		for (j=1; j<=nreqs; ++j) if (!doneset[r[j]])
 		    break
 	    	if (j<=nreqs) {
 		    finished = 0
 		    continue # try a different setting
 		}
 	    }

 	    # All the requirements have been processed, output
 	    # this setting.
 	    if (deb) print "setting", i
 	    print "" >out
 	    print "/* setting: ", i >out
 	    print " *   requires:" setting[i] >out
 	    print " *   default: ", defaults[i], "*/" >out
 	    if (defaults[i] == "") # no default, only check if defined
 		print "#ifdef PNG_" i >out
 	    for (j=1; j<=nreqs; ++j) {
 	    	print "# ifndef PNG_" r[j] >out
 		print error, i, "requires", r[j] end >out
 		print "# endif" >out
 	    }
 	    if (defaults[i] != "") # default handling
 		print "#ifdef PNG_" i >out
 	    print def i, "PNG_" i end >out
 	    if (defaults[i] != "") {
 	    	print "#else /*default*/" >out
 		print def i defaults[i] end >out
 	    }
 	    print "#endif" >out

 	    doneset[i] = 1
 	    ++movement
 	}

 	if (!finished && !movement) {
 	    print "setting: loop or missing setting in 'requires', cannot process:"
 	    for (i in setting) if (!doneset[i])
 	    	print "  setting", i, "requires" setting[i]
 	    exit 1
 	}
     }
     print comment, "end of settings", cend >out

     # Now do the options - somewhat more complex.  The dependency
     # tree is thus:
     #
     #   name    >      name
     #	name requires  name
     #   name if        name
     #   name enabledby name
     #
     # First build a list 'tree' by option of all the things on which
     # it depends.
     print "" >out
     print "/* OPTIONS */" >out
     print comment, "options", cend >out
     for (opt in enabledby) tree[opt] = 1  # may not be explicit options
     for (opt in option) tree[opt] = ""    # so unlisted options marked
     for (opt in tree) {
     	if (tree[opt] == 1) {
 	    tree[opt] = ""
 	    if (option[opt] != "") {
 	    	print "internal error (1)"
 		exit 1
 	    }
 	    # Macros only listed in 'enables' remain off unless
 	    # one of the enabling macros is on.
 	    option[opt] = "off"
 	}

     	split("", list) # clear 'list'
 	# Now add every requires, iffs or enabledby entry to 'list'
 	# so that we can add a unique list of requirements to tree[i]
     	split(requires[opt] iffs[opt] enabledby[opt], r)
 	for (i in r) list[r[i]] = 1
 	for (i in list) tree[opt] = tree[opt] " " i
     }

     # print the tree for extreme debugging
     if (deb > 2) for (i in tree) if (i != "") print i, "depends-on" tree[i]

     # option[i] is now the complete list of all the tokens we may
     # need to output, go through it as above, depth first.
     finished = 0
     while (!finished) {
     	finished = 1
 	movement = 0 # done nothing
 	for (i in option) if (!done[i]) {
 	    nreqs = split(tree[i], r)
 	    if (nreqs > 0) {
 		for (j=1; j<=nreqs; ++j) if (!done[r[j]])
 		    break
 	    	if (j<=nreqs) {
 		    finished = 0
 		    continue  # next option
 		}
 	    }

 	    # All the requirements have been processed, output
 	    # this option.  An option is _SUPPORTED if:
 	    #
 	    # all 'requires' are _SUPPORTED AND
 	    # at least one of the 'if' options are _SUPPORTED AND
 	    # EITHER:
 	    #   The name is _SUPPORTED (on the command line)
 	    # OR:
 	    #   an 'enabledby' is _SUPPORTED
 	    # OR:
 	    #   NO_name is not defined AND
 	    #   the option is not marked "off"
 	    if (deb) print "option", i
 	    print "" >out
 	    print "/* option:", i, option[i] >out
 	    print " *   requires:  " requires[i] >out
 	    print " *   if:        " iffs[i] >out
 	    print " *   enabled-by:" enabledby[i], "*/" >out
 	    print "#undef PNG_on" >out
 	    print "#define PNG_on 1" >out

 	    # requires
 	    nreqs = split(requires[i], r)
 	    for (j=1; j<=nreqs; ++j) {
 	    	print "#ifndef PNG_" r[j] "_SUPPORTED" >out
 		print "#   undef PNG_on /*!" r[j] "*/" >out
 		print "#endif" >out
 	    }

 	    # if
 	    nreqs = split(iffs[i], r)
 	    print "#undef PNG_no_if" >out
 	    if (nreqs > 0) {
 		print "/* if" iffs[i], "*/" >out
 	    	print "#define PNG_no_if 1" >out
 		for (j=1; j<=nreqs; ++j) {
 		    print "#ifdef PNG_" r[j] "_SUPPORTED" >out
 		    print "#   undef PNG_no_if /*" r[j] "*/" >out
 		    print "#endif" >out
 		}
 		print "#ifdef PNG_no_if /*missing if*/" >out
 		print "#   undef PNG_on" >out
 		print "#endif" >out
 	    }

 	    print "#ifdef PNG_on /*requires, if*/" >out
 	    # enables
 	    print "#   undef PNG_not_enabled" >out
 	    print "#   define PNG_not_enabled 1" >out
 	    print "   /* enabled by" enabledby[i], "*/" >out
 	    nreqs = split(enabledby[i], r)
 	    for (j=1; j<=nreqs; ++j) {
 	    	print "#ifdef PNG_" r[j] "_SUPPORTED" >out
 		print "#   undef PNG_not_enabled /*" r[j] "*/" >out
 		print "#endif" >out
 	    }

 	    print "#   ifndef PNG_" i "_SUPPORTED /*!command line*/" >out
 	    print "#     ifdef PNG_not_enabled /*!enabled*/" >out
 	    if (option[i] == "off") {
 		print "#       undef PNG_on /*default off*/" >out
 	    } else {
 		print "#       ifdef PNG_NO_" i >out
 		print "#         undef PNG_on /*turned off*/" >out
 		print "#       endif" >out
 		print "#       ifdef PNG_NO_" i "_SUPPORTED" >out
 		print "#         undef PNG_on /*turned off*/" >out
 		print "#       endif" >out
 	    }
 	    print "#     endif /*!enabled*/" >out
 	    print "#     ifdef PNG_on" >out
 	    # The _SUPPORTED macro must be defined so that dependent
 	    # options output later work.
 	    print "#       define PNG_" i "_SUPPORTED" >out
 	    print "#     endif" >out
 	    print "#   endif /*!command line*/" >out
 	    # If PNG_on is still set the option should be defined in
 	    # pnglibconf.h
 	    print "#   ifdef PNG_on" >out
 	    if (i ~ /^fail_/)
 	        print error, i, "if" iffs[i], "requires" requires[i] end >out
 	    else if (i !~ /^ok_/)
 		print def i sup >out
 	    print "#   endif /* definition */" >out
 	    print "#endif /*requires, if*/" >out
 	    if (logunsupported || i ~ /^ok_/) {
 		print "#ifndef  PNG_on" >out
 		if (logunsupported)
 		    print und i une >out
 		if (i ~ /^ok_/)
 		    print error, i, "if" iffs[i], "requires" requires[i] end >out
 		print "#endif" >out
 	    }

 	    done[i] = 1
 	    ++movement
 	}

 	if (!finished && !movement) {
 	    print "option: loop or missing option in dependency tree, cannot process:"
 	    for (i in option) if (!done[i]) {
 	    	print "  option", i, "depends on" tree[i], "needs:"
 		nreqs = split(tree[i], r)
 		if (nreqs > 0) for (j=1; j<=nreqs; ++j) if (!done[r[j]])
 		    print "    " r[j]
 	    }
 	    exit 1
 	}
     }
     print comment, "end of options", cend >out

     # Regular end - everything looks ok
     if (protect != "")
     	print start "#endif", cx, protect, "*/" end >out
 }
	#!/bin/awk -f
	# scripts/options.awk - library build configuration control
	#
	# last changed in libpng version 1.5.0 - April 27, 2010
	#
	# Copyright (c) 1998-2010 Glenn Randers-Pehrson
	#
	# This code is released under the libpng license.
	# For conditions of distribution and use, see the disclaimer
	# and license in png.h

	# The output of this script is written to the file given by
	# the variable 'out'. The script is run twice, once with
	# an intermediate output file, 'options.tmp' then again on
	# that file to produce the final output. Each time the
	# output files and whether or not to pre-prrocess must be
	# specified:
	#
	# awk -f scripts/options.awk pre=1 out=options.tmp scripts/options.dat 1>&2
	# awk -f scripts/options.awk pre=0 out=options.dfn options.tmp 1>&2

	BEGIN{
	out="/dev/null" # intermediate, preprocessed, file
	pre=-1 # preprocess
	start="PNG_DEFN_MAGIC-" # Arbitrary start
	end="-PNG_DEFN_END" # Arbitrary end
	cx= "/@@@*" # Open C comment for output file
	comment=start cx # Comment start
	cend="*/" end # Comment end
	def=start "#define PNG_@@@" # Arbitrary define
	sup="@@@_SUPPORTED" end # end supported option
	und=comment "#undef PNG_@@@" # Unsupported option
	une="@@@_SUPPORTED" cend # end unsupported option
	error=start "ERROR:" # error message
	deb=0 # debug - set on command line
	logunsupported=0 # write unsupported options too

	# Precreate arrays
	option[""] = "" # list of all options: default on/off/""
	done[""] = 1 # marks option as having been output
	requires[""] = "" # requires by option
	iffs[""] = "" # if by option
	enabledby[""] = "" # options that enable it by option
	setting[""] = "" # requires by setting
	defaults[""] = "" # used for a defaulted value
	doneset[""] = 1 # marks setting as having been output
	r[""] = "" # Temporary array

	# For decorating the output file
	protect = ""
	}

	# Preprocessing - this just copies the input file with lines
	# that need preprocessing (just chunk at present) expanded
	pre && $1 != "chunk"{
	print >out
	next
	}

	# The first characters of the line determine how it is processed,
	# leading spaces are ignored. In general tokens that are not
	# keywords are the names of options. An option 'name' is
	# controlled by the definition of the corresponding macros:
	#
	# PNG_name_SUPPORTED The option is turned on
	# PNG_NO_name
	# PNG_NO_name_SUPPORTED If the first macro is not defined
	# either of these will turn the option off
	#
	# If none of these macros are defined the option is turned on, unless
	# the keyword 'off' is given in a line relating to the option. The
	# keyword 'on' can also be given, but it will be ignored (since it is
	# the default.)
	#
	# In the syntax below a 'name' is indicated by "NAME", other macro
	# values are indicated by "MACRO", as with "NAME" the leading "PNG_"
	# is omitted, but in this case the "NO_" prefix and the "_SUPPORTED"
	# suffix are never used.
	#
	# Each line is introduced by a keyword - the first non-space characters
	# on the line. A line starting with a '#' is a comment - it is totally
	# ignored. Keywords are as follows, a NAME, is simply a macro name
	# without the leading PNG_, PNG_NO_ or the trailing _SUPPORTED.

	$1 ~ /^#/ \|\| $0 ~ /^[ ]*$/{
	next
	}

	# com <comment>
	# The whole line is placed in the output file as a comment with
	# the preceding 'com' removed
	$1 == "com"{
	if (NF > 1) {
	sub(/^[ ]com[ ]/, "")
	print comment, $0, cend >out
	} else
	print start end >out
	next
	}

	# file output input protect
	# Informational: the official name of the input file (without
	# make generated local directories), the official name of the
	# output file and, if required, a name to use in a protection
	# macro for the contents.
	$1 == "file" && NF >= 2{
	print comment, $2, cend >out
	print comment, "Machine generated file: DO NOT EDIT", cend >out
	if (NF >= 3)
	print comment, "Derived from:", $3, cend >out
	protect = $4
	if (protect != "") {
	print start "#ifndef", protect end >out
	print start "#define", protect end >out
	}
	next
	}

	# option NAME ( (requires\|enables\|if) NAME* \| on \| off )*
	# Declares an option 'NAME' and describes its default setting (on\|off)
	# and its relationship to other options. The option is disabled
	# unless all the options listed after 'requires' are set and at
	# least one of the options listed after 'if' is set. If the
	# option is set then it turns on all the options listed after 'enables'.

	$1 == "option" && NF >= 2{
	onoff = option[$2] # records default on or default off
	key = ""
	for (i=3; i<=NF; ++i) {
	if ($(i) == "on" \|\| $(i) == "off") {
	key = ""
	if (onoff != $(i)) {
	if (onoff == "")
	onoff = $(i)
	else {
	# Print a message, otherwise the error
	# below is incomprehensible
	print $2 ": currently", onoff ": attempt to turn", $(i)
	break
	}
	}
	} else if ($(i) == "requires" \|\| $(i) == "if" \|\| $(i) == "enables") {
	key = $(i)
	} else if (key == "requires") {
	requires[$2] = requires[$2] " " $(i)
	} else if (key == "if") {
	iffs[$2] = iffs[$2] " " $(i)
	} else if (key == "enables") {
	enabledby[$(i)] = enabledby[$(i)] " " $2
	} else
	break # bad line format
	}

	if (i > NF) {
	# Set the option - this may explicitly set it to "", that's good
	# becaue we need to ensure it exists and we can't rely on some
	# actually quite sensible awk implementation not optimising the
	# read above away (gawk doesn't)
	option[$2] = onoff
	next
	}
	# Else fall through to the error handler
	}

	# chunk NAME [requires OPT] [off]
	# Expands to the 'option' settings appropriate to the reading and
	# writing of an ancilliary PNG chunk 'NAME':
	#
	# option READ_NAME requires READ_ANCILLARY_CHUNKS [READ_OPT]
	# option READ_NAME enables NAME
	# [option READ_NAME off]
	# option WRITE_NAME requires WRITE_ANCILLARY_CHUNKS [WRITE_OPT]
	# option WRITE_NAME enables NAME
	# [option WRITE_NAME off]

	pre && $1 == "chunk" && NF >= 2{
	# 'chunk' is handled on the first pass by writing appropriate
	# 'option' lines into the intermediate file.
	onoff = ""
	reqread = ""
	reqwrite = ""
	i = 3 # indicates format error
	if (NF > 2) {
	# read the keywords/additional OPTS
	req = 0
	for (i=3; i<=NF; ++i) {
	if ($(i) == "on" \|\| $(i) == "off") {
	if (onoff != $(i)) {
	if (onoff == "")
	onoff = $(i)
	else
	break # on/off conflict
	}
	} else if ($(i) == "requires")
	req = 1
	else if (req != 1)
	break # bad line: handled below
	else {
	reqread = reqread " READ_" $(i)
	reqwrite = reqwrite " WRITE_" $(i)
	}
	}
	}

	if (i > NF) {
	# Output new 'option' lines to the intermediate file (out)
	print "option READ_" $2,
	"requires READ_ANCILLARY_CHUNKS" reqread,
	"enables", $2, onoff >out
	print "option WRITE_" $2,
	"requires WRITE_ANCILLARY_CHUNKS" reqwrite,
	"enables", $2, onoff >out
	next
	}
	# Else hit the error handler below - bad line format!
	}

	# setting MACRO ( requires MACRO* )* [ default VALUE ]
	# Behaves in a similar way to 'option' without looking for NO_ or
	# _SUPPORTED; the macro is enabled if it is defined so long as all
	# the 'requires' macros are also defined. The definitions may be
	# empty, an error will be issued if the 'requires' macros are
	# not defined. If given the 'default' value is used if the
	# macro is not defined. The default value will be re-tokenised.
	# (BTW: this is somewhat restrictive, it mainly exists for the
	# support of non-standard configurations and numeric parameters,
	# see the uses in scripts/options.dat

	$1 == "setting" && (NF == 2 \|\| NF >= 3 && ($3 == "requires" \|\| $3 == "default")){
	reqs = ""
	deflt = ""
	isdef = 0
	key = ""
	for (i=3; i<=NF; ++i)
	if ($(i) == "requires" \|\| $(i) == "default") {
	key = $(i)
	if (key == "default") isdef = 1
	} else if (key == "requires")
	reqs = reqs " " $(i)
	else if (key == "default")
	deflt = deflt " " $(i)
	else
	break # Format error, handled below

	setting[$2] = reqs
	if (isdef && deflt == "")
	deflt = " " # as a flag to force output
	defaults[$2] = deflt
	next
	}

	# The order of the dependency lines (option, chunk, setting) is irrelevant
	# - the 'enables', 'requires' and 'if' settings will be used to determine
	# the correct order in the output and the final values in pnglibconf.h are
	# not order dependent. 'requires' and 'if' entries take precedence over
	# 'enables' from other options; if an option requires another option it
	# won't be set regardless of any options that enable it unless the other
	# option is also enabled.
	#
	# Similarly 'enables' trumps a NO_ definition in CFLAGS or pngusr.h
	#
	# For simplicity cycles in the definitions are regarded as errors,
	# even if they are not ambiguous.
	# A given NAME can be specified in as many 'option' lines as required, the
	# definitions are additive.

	# For backwards compatibility equivalent macros may be listed thus:
	#
	# = [NO_]NAME MACRO
	# Makes -DMACRO equivalent to -DPNG_NO_NAME or -DPNG_NAME_SUPPORTED
	# as appropriate.
	#
	# The definition is injected into the C compiler input when encountered
	# in the second pass (so all these definitions appear after the @
	# lines!)
	#
	# 'NAME' is as above, but 'MACRO' is the full text of the equivalent
	# old, deprecated, macro.

	$1 == "=" && NF == 3{
	print "#ifdef PNG_" $3 >out
	if ($2 ~ /^NO_/)
	print "# define PNG_" $2 >out
	else
	print "# define PNG_" $2 "_SUPPORTED" >out
	print "#endif" >out
	next
	}

	# Lines may be injected into the C compiler input by preceding them
	# with an "@" character. The line is copied with just the leading
	# @ removed.

	$1 ~ /^@/{
	sub(/^[ ]*@/, "")
	print >out
	next
	}

	# Check for unreognized lines, because of the preprocessing chunk
	# format errors will be detected on the first pass independent of
	# any other format errors.
	{
	print "options.awk: bad line (" NR "):", $0
	exit 1
	}

	# For checking purposes names that start with "ok_" or "fail_" are
	# not output to pnglibconf.h and must be either enabled or disabled
	# respectively for the build to succeed. This allows interdependencies
	# between options of the form "at least one of" or "at most one of"
	# to be checked. For example:
	#
	# option FLOATING_POINT enables ok_math
	# option FIXED_POINT enables ok_math
	# This ensures that at least one of FLOATING_POINT and FIXED_POINT
	# must be set for the build to succeed.
	#
	# option fail_math requires FLOATING_POINT FIXED_POINT
	# This means the build will fail if both FLOATING_POINT and
	# FIXED_POINT are set (this is an example; in fact both are allowed.)
	#
	# If all these options were given the build would require exactly one
	# of the names to be enabled.

	END{
	if (out == "/dev/null") {
	print "out=output.file must be given on the command line"
	exit 1
	}
	if (pre) {
	if (pre != 1) {
	print "pre=0 or pre=1 must be given on command line"
	exit 1
	}
	exit 0
	}

	# Do the 'setting' values first, the algorithm the standard
	# tree walk (O(1)) done in an O(2) while/for loop; interations
	# settings x depth, outputing the deepest required macros
	# first.
	print "" >out
	print "/* SETTINGS */" >out
	print comment, "settings", cend >out
	finished = 0
	while (!finished) {
	finished = 1
	movement = 0 # done nothing
	for (i in setting) if (!doneset[i]) {
	nreqs = split(setting[i], r)
	if (nreqs > 0) {
	for (j=1; j<=nreqs; ++j) if (!doneset[r[j]])
	break
	if (j<=nreqs) {
	finished = 0
	continue # try a different setting
	}
	}

	# All the requirements have been processed, output
	# this setting.
	if (deb) print "setting", i
	print "" >out
	print "/* setting: ", i >out
	print " * requires:" setting[i] >out
	print " * default: ", defaults[i], "*/" >out
	if (defaults[i] == "") # no default, only check if defined
	print "#ifdef PNG_" i >out
	for (j=1; j<=nreqs; ++j) {
	print "# ifndef PNG_" r[j] >out
	print error, i, "requires", r[j] end >out
	print "# endif" >out
	}
	if (defaults[i] != "") # default handling
	print "#ifdef PNG_" i >out
	print def i, "PNG_" i end >out
	if (defaults[i] != "") {
	print "#else /default/" >out
	print def i defaults[i] end >out
	}
	print "#endif" >out

	doneset[i] = 1
	++movement
	}

	if (!finished && !movement) {
	print "setting: loop or missing setting in 'requires', cannot process:"
	for (i in setting) if (!doneset[i])
	print " setting", i, "requires" setting[i]
	exit 1
	}
	}
	print comment, "end of settings", cend >out

	# Now do the options - somewhat more complex. The dependency
	# tree is thus:
	#
	# name > name
	# name requires name
	# name if name
	# name enabledby name
	#
	# First build a list 'tree' by option of all the things on which
	# it depends.
	print "" >out
	print "/* OPTIONS */" >out
	print comment, "options", cend >out
	for (opt in enabledby) tree[opt] = 1 # may not be explicit options
	for (opt in option) tree[opt] = "" # so unlisted options marked
	for (opt in tree) {
	if (tree[opt] == 1) {
	tree[opt] = ""
	if (option[opt] != "") {
	print "internal error (1)"
	exit 1
	}
	# Macros only listed in 'enables' remain off unless
	# one of the enabling macros is on.
	option[opt] = "off"
	}

	split("", list) # clear 'list'
	# Now add every requires, iffs or enabledby entry to 'list'
	# so that we can add a unique list of requirements to tree[i]
	split(requires[opt] iffs[opt] enabledby[opt], r)
	for (i in r) list[r[i]] = 1
	for (i in list) tree[opt] = tree[opt] " " i
	}

	# print the tree for extreme debugging
	if (deb > 2) for (i in tree) if (i != "") print i, "depends-on" tree[i]

	# option[i] is now the complete list of all the tokens we may
	# need to output, go through it as above, depth first.
	finished = 0
	while (!finished) {
	finished = 1
	movement = 0 # done nothing
	for (i in option) if (!done[i]) {
	nreqs = split(tree[i], r)
	if (nreqs > 0) {
	for (j=1; j<=nreqs; ++j) if (!done[r[j]])
	break
	if (j<=nreqs) {
	finished = 0
	continue # next option
	}
	}

	# All the requirements have been processed, output
	# this option. An option is _SUPPORTED if:
	#
	# all 'requires' are _SUPPORTED AND
	# at least one of the 'if' options are _SUPPORTED AND
	# EITHER:
	# The name is _SUPPORTED (on the command line)
	# OR:
	# an 'enabledby' is _SUPPORTED
	# OR:
	# NO_name is not defined AND
	# the option is not marked "off"
	if (deb) print "option", i
	print "" >out
	print "/* option:", i, option[i] >out
	print " * requires: " requires[i] >out
	print " * if: " iffs[i] >out
	print " * enabled-by:" enabledby[i], "*/" >out
	print "#undef PNG_on" >out
	print "#define PNG_on 1" >out

	# requires
	nreqs = split(requires[i], r)
	for (j=1; j<=nreqs; ++j) {
	print "#ifndef PNG_" r[j] "_SUPPORTED" >out
	print "# undef PNG_on /!" r[j] "/" >out
	print "#endif" >out
	}

	# if
	nreqs = split(iffs[i], r)
	print "#undef PNG_no_if" >out
	if (nreqs > 0) {
	print "/* if" iffs[i], "*/" >out
	print "#define PNG_no_if 1" >out
	for (j=1; j<=nreqs; ++j) {
	print "#ifdef PNG_" r[j] "_SUPPORTED" >out
	print "# undef PNG_no_if /" r[j] "/" >out
	print "#endif" >out
	}
	print "#ifdef PNG_no_if /missing if/" >out
	print "# undef PNG_on" >out
	print "#endif" >out
	}

	print "#ifdef PNG_on /requires, if/" >out
	# enables
	print "# undef PNG_not_enabled" >out
	print "# define PNG_not_enabled 1" >out
	print " /* enabled by" enabledby[i], "*/" >out
	nreqs = split(enabledby[i], r)
	for (j=1; j<=nreqs; ++j) {
	print "#ifdef PNG_" r[j] "_SUPPORTED" >out
	print "# undef PNG_not_enabled /" r[j] "/" >out
	print "#endif" >out
	}

	print "# ifndef PNG_" i "_SUPPORTED /!command line/" >out
	print "# ifdef PNG_not_enabled /!enabled/" >out
	if (option[i] == "off") {
	print "# undef PNG_on /default off/" >out
	} else {
	print "# ifdef PNG_NO_" i >out
	print "# undef PNG_on /turned off/" >out
	print "# endif" >out
	print "# ifdef PNG_NO_" i "_SUPPORTED" >out
	print "# undef PNG_on /turned off/" >out
	print "# endif" >out
	}
	print "# endif /!enabled/" >out
	print "# ifdef PNG_on" >out
	# The _SUPPORTED macro must be defined so that dependent
	# options output later work.
	print "# define PNG_" i "_SUPPORTED" >out
	print "# endif" >out
	print "# endif /!command line/" >out
	# If PNG_on is still set the option should be defined in
	# pnglibconf.h
	print "# ifdef PNG_on" >out
	if (i ~ /^fail_/)
	print error, i, "if" iffs[i], "requires" requires[i] end >out
	else if (i !~ /^ok_/)
	print def i sup >out
	print "# endif /* definition */" >out
	print "#endif /requires, if/" >out
	if (logunsupported \|\| i ~ /^ok_/) {
	print "#ifndef PNG_on" >out
	if (logunsupported)
	print und i une >out
	if (i ~ /^ok_/)
	print error, i, "if" iffs[i], "requires" requires[i] end >out
	print "#endif" >out
	}

	done[i] = 1
	++movement
	}

	if (!finished && !movement) {
	print "option: loop or missing option in dependency tree, cannot process:"
	for (i in option) if (!done[i]) {
	print " option", i, "depends on" tree[i], "needs:"
	nreqs = split(tree[i], r)
	if (nreqs > 0) for (j=1; j<=nreqs; ++j) if (!done[r[j]])
	print " " r[j]
	}
	exit 1
	}
	}
	print comment, "end of options", cend >out

	# Regular end - everything looks ok
	if (protect != "")
	print start "#endif", cx, protect, "*/" end >out
	}