From 141d9e3c20c6fc2c497ab2e5699c96442040e002 Mon Sep 17 00:00:00 2001
From: Glenn Randers-Pehrson <glennrp at users.sourceforge.net>
Date: Mon, 13 Jun 2011 11:47:00 -0500
Subject: [PATCH] [devel] Made it possible to undefine
 PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED

to get the same (inaccurate) output as libpng-1.5.2 and earlier.
---
 ANNOUNCE   | 20 ++++++++++++--------
 CHANGES    |  4 ++++
 pngrtran.c | 13 +++++++++++++
 3 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/ANNOUNCE b/ANNOUNCE
index 161e53c37..fbabdb663 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.5.3beta11 - June 11, 2011
+Libpng 1.5.3beta12 - June 13, 2011
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -9,20 +9,20 @@ Files available for download:
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   1.5.3beta11.tar.xz (LZMA-compressed, recommended)
-   1.5.3beta11.tar.gz
-   1.5.3beta11.tar.bz2
+   1.5.3beta12.tar.xz (LZMA-compressed, recommended)
+   1.5.3beta12.tar.gz
+   1.5.3beta12.tar.bz2
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lp153b11.7z  (LZMA-compressed, recommended)
-   lp153b11.zip
+   lp153b12.7z  (LZMA-compressed, recommended)
+   lp153b12.zip
 
 Other information:
 
-   1.5.3beta11-README.txt
-   1.5.3beta11-LICENSE.txt
+   1.5.3beta12-README.txt
+   1.5.3beta12-LICENSE.txt
 
 Changes since the last public release (1.5.2):
 
@@ -181,6 +181,10 @@ Version 1.5.3beta11 [June 11, 2011]
     necessarily fully supportable, particularly png_strncpy and png_snprintf.
   Added log option to pngvalid.c and attempted to improve gamma messages.
 
+Version 1.5.3beta12 [June 13, 2011]
+  Made it possible to undefine PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+    to get the same (inaccurate) output as libpng-1.5.2 and earlier.
+
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
diff --git a/CHANGES b/CHANGES
index f42bac020..c9571eae7 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3443,6 +3443,10 @@ Version 1.5.3beta11 [June 11, 2011]
   Removed string/memory macros that are no longer used and are not
     necessarily fully supportable, particularly png_strncpy and png_snprintf.
   Added log option to pngvalid.c and attempted to improve gamma messages.
+  
+Version 1.5.3beta12 [June 13, 2011]
+  Made it possible to undefine PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+    to get the same (inaccurate) output as libpng-1.5.2 and earlier.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngrtran.c b/pngrtran.c
index 86c0558a5..5fb6f4840 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -1439,7 +1439,11 @@ png_init_read_transformations(png_structp png_ptr)
        * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
        * present, so that case is ok (until do_expand_16 is moved.)
        */
+#ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
 #     define CHOP(x) (x)=((png_uint_16)(((png_uint_32)(x)*255+32895) >> 16))
+#else
+#     define CHOP(x) ((png_uint_16)((2*(png_uint_32)(x) + 257)/514))
+#endif
       CHOP(png_ptr->background.red);
       CHOP(png_ptr->background.green);
       CHOP(png_ptr->background.blue);
@@ -2494,9 +2498,18 @@ png_do_chop(png_row_infop row_info, png_bytep row)
           *
           *    (V * 255 + 32895) >> 16
           */
+
+#ifdef PNG_LEGACY_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+         *dp = *sp + ((((int)(*(sp + 1)) - *sp) > 128) ? 1 : 0);
+#else
          png_int_32 tmp = *sp++; /* must be signed! */
+#  ifdef PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
          tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
+#  else
+         sp++;
+#  endif
          *dp++ = (png_byte)tmp;
+#endif
       }
 
       row_info->bit_depth = 8;