[libpng17] Make ARM NEON support work at compile time (not just configure time).

This moves the test on __ARM_NEON__ into pngconf.h to avoid issues when
using a compiler that compiles for multiple architectures at one time.

ANNOUNCE

@@ -309,6 +309,9 @@ Version 1.7.0beta14 [June 6, 2013]
   Added set(CMAKE_CONFIGURATION_TYPES ...) to CMakeLists.txt (Andrew Hundt)
   Deleted set(CMAKE_BUILD_TYPE) block from CMakeLists.txt
   Enclose the prototypes for the simplified write API in #ifdef STDIO/#endif
+  Make ARM NEON support work at compile time (not just configure time).
+    This moves the test on __ARM_NEON__ into pngconf.h to avoid issues when
+    using a compiler that compiles for multiple architectures at one time.
 
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CHANGES

@@ -4597,6 +4597,9 @@ Version 1.7.0beta14 [June 6, 2013]
   Added set(CMAKE_CONFIGURATION_TYPES ...) to CMakeLists.txt (Andrew Hundt)
   Deleted set(CMAKE_BUILD_TYPE) block from CMakeLists.txt
   Enclose the prototypes for the simplified write API in #ifdef STDIO/#endif
+  Make ARM NEON support work at compile time (not just configure time).
+    This moves the test on __ARM_NEON__ into pngconf.h to avoid issues when
+    using a compiler that compiles for multiple architectures at one time.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit

configure.ac

@@ -347,11 +347,12 @@ AC_ARG_ENABLE([arm-neon],
       [Enable ARM NEON optimizations: =no/off, check, api, yes/on:]
       [no/off: disable the optimizations; check: use internal checking code]
       [(deprecated and poorly supported); api: disable by default, enable by]
-      [a call to png_set_option; yes/on: turn on unconditionally.]),
+      [a call to png_set_option; yes/on: turn on unconditionally.]
+      [If not specified: determined by the compiler.]),
    [case "$enableval" in
       no|off)
          # disable the default enabling on __ARM_NEON__ systems:
-         AC_DEFINE([PNG_NO_ARM_NEON], [],
+         AC_DEFINE([PNG_ARM_NEON_NOT_SUPPORTED], [],
                    [Disable ARM Neon optimizations])
          # Prevent inclusion of the assembler files below:
          enable_arm_neon=no;;

pngconf.h

@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.7.0beta14 - May 13, 2013
+ * libpng version 1.7.0beta14 - June 6, 2013
  *
  * Copyright (c) 1998-2013 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -194,6 +194,30 @@
  *                PNG_USE_DLL is set.
  */
 
+/* Compile time options.
+ * =====================
+ * In a multi-arch build the compiler may compile the code several times for the
+ * same object module, producing different codes for different architectures.
+ * When this happens configure-time setting of the target host options cannot be
+ * done and this interferes with the handling of the ARM NEON optimizations, and
+ * possibly other similiar optimizations.  Put additional tests here; in general
+ * this is needed when the same option can be changed at both compile time and
+ * run time depending on the target OS (i.e. iOS vs Android.)
+ */
+#ifdef __ARM_NEON__
+   /* If the default below causes problems set PNG_ARM_NEON_NOT_SUPPORTED either
+    * by passing --enable-arm-neon=no to configure or setting it in some other
+    * way when pnglibconf.h is built.
+    */
+#  if (!defined PNG_ARM_NEON_SUPPORTED) && (!defined PNG_ARM_NEON_NOT_SUPPORTED)
+#     define PNG_ARM_NEON_SUPPORTED
+#  endif
+#endif
+
+#if (defined PNG_ARM_NEON_SUPPORTED) && (defined PNG_ARM_NEON_NOT_SUPPORTED)
+#  error configuration: ARM_NEON cannot both be supported and disabled
+#endif
+
 /* System specific discovery.
  * ==========================
  * This code is used at build time to find PNG_IMPEXP, the API settings

scripts/pnglibconf.dfa

@@ -165,12 +165,6 @@ logunsupported = 1
 @#  endif
 @#endif
 
-# This changes the default for the ARM NEON optimizations according to
-# __ARM_NEON__
-@#ifdef __ARM_NEON__
-@#  define PNG_ARM_NEON_SUPPORTED
-@#endif
-
 # IN DEVELOPMENT
 # These are currently experimental features; define them if you want (NOTE:
 # experimental options must be disabled before they are defined in this file!)
@@ -236,6 +230,8 @@ option SET_OPTION disabled
 # These options are specific to the ARM NEON hardware optimizations:
 #
 # ARM_NEON: the optimization itself
+# ARM_NEON_NOT: disable the optimization even on systems that apparently support
+#               it (where the compiler defines __ARM_NEON__).
 # ARM_NEON_API: allow the optimization to be switched on with png_set_hardware
 # ARM_NEON_CHECK: compile a run-time check to see if Neon extensions are
 setting ZLIB_VERNUM default @ZLIB_VERNUM
@@ -243,6 +239,7 @@ setting ZLIB_VERNUM default @ZLIB_VERNUM
 #                 png_set_hardware API.
 option ARM_NEON disabled,
    sets FILTER_OPTIMIZATIONS png_init_filter_functions_neon
+option ARM_NEON_NOT disabled
 option ARM_NEON_API disabled enables SET_OPTION ARM_NEON
 option ARM_NEON_CHECK disabled enables ARM_NEON