api(Windows): Remove the ordinals attached to exported functions

In order to make ABI compatibility guarantees about the Windows DLL,
we had to keep maintaining the API ordinals consistently. As we are
now designing a fresh new ABI, we use this opportunity to stop using
ordinals altogether.

Exporting API functions by ordinal numbers instead of names was a
necessity in the early (16-bit) versions of Windows, by design, to
minimize the memory requirements. Although using ordinals was still
possible in all subsequent versions of Windows, it was no longer
necessary from the 32-bit versions of Windows onwards.

The libpng DLL will still have ordinals, assigned arbitrarily, but
the dynamic linking of applications to this DLL will be done by name.
(The applications that use the zlib DLL operate in the same manner.)

Author: ctruta

png.h

@@ -290,13 +290,8 @@
 #  define PNG_EXPORT_TYPE(type) PNG_IMPEXP type
 #endif
 
-   /* The ordinal value is only relevant when preprocessing png.h for symbol
-    * table entries, so we discard it here.  See the .dfn files in the
-    * scripts directory.
-    */
-
 #ifndef PNG_EXPORTA
-#  define PNG_EXPORTA(ordinal, type, name, args, attributes) \
+#  define PNG_EXPORTA(type, name, args, attributes) \
       PNG_FUNCTION(PNG_EXPORT_TYPE(type), (PNGAPI name), args, \
       PNG_LINKAGE_API attributes)
 #endif
@@ -306,12 +301,11 @@
  */
 #define PNG_EMPTY /*empty list*/
 
-#define PNG_EXPORT(ordinal, type, name, args) \
-   PNG_EXPORTA(ordinal, type, name, args, PNG_EMPTY)
+#define PNG_EXPORT(type, name, args) PNG_EXPORTA(type, name, args, PNG_EMPTY)
 
 /* Use PNG_REMOVED to comment out a removed interface. */
 #ifndef PNG_REMOVED
-#  define PNG_REMOVED(ordinal, type, name, args, attributes)
+#  define PNG_REMOVED(type, name, args, attributes)
 #endif
 
 #ifndef PNG_CALLBACK
@@ -446,18 +440,16 @@
 
 #ifndef PNG_FP_EXPORT     /* A floating point API. */
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
-#     define PNG_FP_EXPORT(ordinal, type, name, args)\
-         PNG_EXPORT(ordinal, type, name, args);
+#     define PNG_FP_EXPORT(type, name, args) PNG_EXPORT(type, name, args);
 #  else                   /* No floating point APIs */
-#     define PNG_FP_EXPORT(ordinal, type, name, args)
+#     define PNG_FP_EXPORT(type, name, args)
 #  endif
 #endif
 #ifndef PNG_FIXED_EXPORT  /* A fixed point API. */
 #  ifdef PNG_FIXED_POINT_SUPPORTED
-#     define PNG_FIXED_EXPORT(ordinal, type, name, args)\
-         PNG_EXPORT(ordinal, type, name, args);
+#     define PNG_FIXED_EXPORT(type, name, args) PNG_EXPORT(type, name, args);
 #  else                   /* No fixed point APIs */
-#     define PNG_FIXED_EXPORT(ordinal, type, name, args)
+#     define PNG_FIXED_EXPORT(type, name, args)
 #  endif
 #endif
 

pngconf.h

@@ -1,6 +1,6 @@
 /* pngpriv.h - private declarations for use inside libpng
  *
- * Copyright (c) 2018-2024 Cosmin Truta
+ * Copyright (c) 2018-2025 Cosmin Truta
  * Copyright (c) 1998-2002,2004,2006-2018 Glenn Randers-Pehrson
  * Copyright (c) 1996-1997 Andreas Dilger
  * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
@@ -185,7 +185,7 @@
  */
 #ifndef PNG_FP_EXPORT
 #  ifndef PNG_FLOATING_POINT_SUPPORTED
-#     define PNG_FP_EXPORT(ordinal, type, name, args)\
+#     define PNG_FP_EXPORT(type, name, args)\
          PNG_INTERNAL_FUNCTION(type, name, args, PNG_EMPTY);
 #     ifndef PNG_VERSION_INFO_ONLY
          typedef struct png_incomplete png_double;
@@ -197,7 +197,7 @@
 #endif
 #ifndef PNG_FIXED_EXPORT
 #  ifndef PNG_FIXED_POINT_SUPPORTED
-#     define PNG_FIXED_EXPORT(ordinal, type, name, args)\
+#     define PNG_FIXED_EXPORT(type, name, args)\
          PNG_INTERNAL_FUNCTION(type, name, args, PNG_EMPTY);
 #  endif
 #endif

pngpriv.h

@@ -17,40 +17,19 @@
 BEGIN {
    err = 0
    master = ""        # master file
-   official[1] = ""   # defined symbols from master file
-   symbol[1] = ""     # defined symbols from png.h
-   removed[1] = ""    # removed symbols from png.h
-   lasto = 0          # last ordinal value from png.h
-   mastero = 0        # highest ordinal in master file
-   symbolo = 0        # highest ordinal in png.h
+   official[""] = ""  # defined symbols from master file
+   symbol[""] = ""    # defined symbols from png.h
+   removed[""] = ""   # removed symbols from png.h
    missing = "error"  # log an error on missing symbols
    of = "symbols.new" # default to a fixed name
 }
 
 # Read existing definitions from the master file (the first
-# file on the command line.)  This must be a def file and it
-# has definition lines (others are ignored) of the form:
-#
-#   symbol @ordinal
-#
+# file on the command line.)  This is a Windows .def file
+# which must NOT have definitions of the form "symbol @ordinal".
 master == "" {
    master = FILENAME
 }
-FILENAME == master && NF == 2 && $2 ~ /^@/ && $1 !~ /^;/ {
-   o = 0 + substr($2, 2)
-   if (o > 0) {
-      if (official[o] == "") {
-         official[o] = $1
-         if (o > mastero) mastero = o
-         next
-      } else {
-         print master ": duplicated symbol:", official[o] ":", $0
-      }
-   } else {
-      print master ": bad export line format:", $0
-   }
-   err = 1
-}
 FILENAME == master && $1 == ";missing" && NF == 2 {
    # This allows the master file to control how missing symbols
    # are handled; symbols that aren't in either the master or
@@ -62,67 +41,36 @@ FILENAME == master {
    next
 }
 
-# Read new definitions, these are free form but the lines must
+# Read the definitions, which are free-form, but the lines must
 # just be symbol definitions.  Lines will be commented out for
 # 'removed' symbols, introduced in png.h using PNG_REMOVED rather
-# than PNG_EXPORT.  Use symbols.dfn or pngwin.dfn to generate the
-# input file.
+# than PNG_EXPORT.  Use symbols.dfn to generate the input file.
 #
-#  symbol @ordinal   # two fields, exported symbol
-#  ; symbol @ordinal # three fields, removed symbol
-#  ; @ordinal        # two fields, the last ordinal
-NF == 2 && $1 == ";" && $2 ~ /^@[1-9][0-9]*$/ {
-   # last ordinal
-   o = 0 + substr($2, 2)
-   if (lasto == 0 || lasto == o) {
-      lasto = o
-   } else {
-      print "png.h: duplicated last ordinal:", lasto, o
-      err = 1
-   }
+#  symbol   # one field, exported symbol
+#  ; symbol # two fields, removed symbol
+#
+NF == 0 {
+   # empty line
    next
 }
-NF == 3 && $1 == ";" && $3 ~ /^@[1-9][0-9]*$/ {
-   # removed symbol
-   o = 0 + substr($3, 2)
-   if (removed[o] == "" || removed[o] == $2) {
-      removed[o] = $2
-      if (o > symbolo) symbolo = o
-   } else {
-      print "png.h: duplicated removed symbol", o ": '" removed[o] "' != '" $2 "'"
-      err = 1
-   }
+NF == 1 && $1 ~ /^[A-Za-z_][A-Za-z_0-9]*$/ {
+   # exported symbol (one field)
+   symbol[$1] = $1
    next
 }
-NF == 2 && $2 ~ /^@[1-9][0-9]*$/ {
-   # exported symbol
-   o = 0 + substr($2, 2)
-   if (symbol[o] == "" || symbol[o] == $1) {
-      symbol[o] = $1
-      if (o > symbolo) symbolo = o
-   } else {
-      print "png.h: duplicated symbol", o ": '" symbol[o] "' != '" $1 "'"
-      err = 1
-   }
+NF == 2 && $1 == ";" && $2 ~ /^[A-Za-z_][A-Za-z_0-9]*$/ {
+   # removed symbol (two fields)
+   removed[$1] = $1
+   next
 }
 {
-   next # skip all other lines
+   print "error: invalid line:", $0
+   err = 1
+   next
 }
 
-# At the end check for symbols marked as both duplicated and removed
 END {
-   if (symbolo > lasto) {
-      print "highest symbol ordinal in png.h,",
-            symbolo ", exceeds last ordinal from png.h", lasto
-      err = 1
-   }
-   if (mastero > lasto) {
-      print "highest symbol ordinal in", master ",",
-            mastero ", exceeds last ordinal from png.h", lasto
-      err = 1
-   }
-   unexported = 0
-   # Add a standard header to symbols.new:
+   # Write the standard header to "symbols.new":
    print ";Version INSERT-VERSION-HERE" >of
    print ";--------------------------------------------------------------" >of
    print "; LIBPNG symbol list as a Win32 DEF file" >of
@@ -132,59 +80,22 @@ END {
    print "" >of
    print "EXPORTS" >of
 
-   for (o = 1; o <= lasto; ++o) {
-      if (symbol[o] == "" && removed[o] == "") {
-         if (unexported == 0) unexported = o
-         if (official[o] == "") {
-            # missing in export list too, so ok
-            if (o < lasto) continue
-         }
-      }
-      if (unexported != 0) {
-         # Symbols in the .def but not in the new file are errors, but
-         # the 'unexported' symbols aren't in either.  By default this
-         # is an error too (see the setting of 'missing' at the start),
-         # but this can be reset on the command line or by stuff in the
-         # file - see the comments above.
-         if (missing != "ignore") {
-            if (o - 1 > unexported) {
-               print "png.h:", missing ": missing symbols:", unexported "-" o - 1
-            } else {
-               print "png.h:", missing ": missing symbol:", unexported
-            }
-            if (missing != "warning") {
-               err = 1
-            }
-         }
-         unexported = 0
-      }
-      if (symbol[o] != "" && removed[o] != "") {
-         print "png.h: symbol", o,
-               "both exported as '" symbol[o] "' and removed as '" removed[o] "'"
-         err = 1
-      } else if (symbol[o] != official[o]) {
-         # either the symbol is missing somewhere or it changed
-         err = 1
-         if (symbol[o] == "") {
-            print "png.h: symbol", o,
-                  "is exported as '" official[o] "' in", master
-         } else if (official[o] == "") {
-            print "png.h: exported symbol", o,
-                  "'" symbol[o] "' not present in", master
-         } else {
-            print "png.h: exported symbol", o,
-                  "'" symbol[o] "' exists as '" official[o] "' in", master
-         }
-      }
+   # Collect all unique symbols into a plain array for sorting.
+   i = 1
+   for (sym in symbol) {
+      if (sym != "") sorted_symbols[i++] = sym
+   }
 
-      # Finally generate symbols.new
-      if (symbol[o] != "") {
-         print " " symbol[o], "@" o > of
-      }
+   # Sort and print the symbols.
+   asort(sorted_symbols)
+   for (i = 1; i <= length(sorted_symbols); i++) {
+      print " " sorted_symbols[i] >of
    }
 
    if (err != 0) {
       print "*** A new list is in", of, "***"
       exit 1
    }
+
+   # TODO: Check for symbols that are both defined and removed.
 }

scripts/checksym.awk

@@ -1,13 +1,14 @@
 /* prefix.c - generate an unprefixed symbol list
  *
+ * Copyright (c) 2025 Cosmin Truta
  * Copyright (c) 2013-2014 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
  */
 
-#define PNG_EXPORTA(ordinal, type, name, args, attributes)\
+#define PNG_EXPORTA(type, name, args, attributes)\
         PNG_DFN "@" name "@"
 
 /* The configuration information *before* the additional of symbol renames,

scripts/prefix.c

@@ -1,13 +1,14 @@
 /* sym.c - define format of libpng.sym
  *
+ * Copyright (c) 2025 Cosmin Truta
  * Copyright (c) 2011-2014 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
  */
 
-#define PNG_EXPORTA(ordinal, type, name, args, attributes)\
+#define PNG_EXPORTA(type, name, args, attributes)\
         PNG_DFN "@" SYMBOL_PREFIX "@@" name "@"
 
 #include "../png.h"

scripts/sym.c

@@ -1,5 +1,6 @@
 /* symbols.c - find all exported symbols
  *
+ * Copyright (c) 2025 Cosmin Truta
  * Copyright (c) 2011-2014 Glenn Randers-Pehrson
  *
  * This code is released under the libpng license.
@@ -14,12 +15,10 @@
  * scripts/pnglibconf.dfa then this checks the .dfa file too.
  */
 
-#define PNG_EXPORTA(ordinal, type, name, args, attributes)\
-        PNG_DFN "@" name "@ @@" ordinal "@"
-#define PNG_REMOVED(ordinal, type, name, args, attributes)\
-        PNG_DFN "; @" name "@ @@" ordinal "@"
-#define PNG_EXPORT_LAST_ORDINAL(ordinal)\
-        PNG_DFN "; @@" ordinal "@"
+#define PNG_EXPORTA(type, name, args, attributes)\
+        PNG_DFN "@" name "@"
+#define PNG_REMOVED(type, name, args, attributes)\
+        PNG_DFN "; @" name "@"
 
 /* Read the defaults, but use scripts/pnglibconf.h.prebuilt; the 'standard'
  * header file.