[master] Improved the optimization of the zlib CMF byte

(see libpng-1.2.6beta03).

3 files changed, 26 insertions, 3 deletions

diff --git a/ANNOUNCE b/ANNOUNCE
index b50c546b2..86406edbd 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.4.6rc02 - April 3, 2011
+Libpng 1.4.6rc02 - April 6, 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.
@@ -67,7 +67,11 @@ version 1.4.6beta07 [March 22, 2011]
   Fixed a bug (present since libpng-1.0.7) that makes png_handle_sPLT() fail
     to compile when PNG_NO_POINTER_INDEXING is defined (Chubanov Kirill)
 
-version 1.4.6rc01 [April 3, 2011]
+version 1.4.6rc01 [March 31, 2011]
+  No changes.
+
+version 1.4.6rc02 [April 6, 2011]
+  Improved the optimization of the zlib CMF byte (see libpng-1.2.6beta03).
 
 Send comments/corrections/commendations to glennrp at users.sourceforge.net
 or to png-mng-implement at lists.sf.net (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 3095b7bf6..12f6bccac 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2779,7 +2779,11 @@ version 1.4.6beta07 [March 22, 2011]
   Fixed a bug (present since libpng-1.0.7) that makes png_handle_sPLT() fail
     to compile when PNG_NO_POINTER_INDEXING is defined (Chubanov Kirill)
 
-version 1.4.6rc01 [April 3, 2011]
+version 1.4.6rc01 [March 31, 2011]
+  No changes.
+
+version 1.4.6rc02 [April 6, 2011]
+  Improved the optimization of the zlib CMF byte (see libpng-1.2.6beta03).
 
 Send comments/corrections/commendations to glennrp at users.sourceforge.net
 or to png-mng-implement at lists.sf.net (subscription required; visit
diff --git a/pngwutil.c b/pngwutil.c
index 8f7c7c24d..b73c6a9d9 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -682,9 +682,24 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
          if (length >= 2 &&
              png_ptr->height < 16384 && png_ptr->width < 16384)
          {
+            /* Compute the maximum possible length of the datastream */
+
+            /* Number of pixels, plus for each row a filter byte and possible
+             * and possibly a padding byte, so increase the maximum
+             * size to account for these.
+             */
             png_uint_32 uncompressed_idat_size = png_ptr->height *
                ((png_ptr->width *
                png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
+
+            /* If it's interlaced, each block of 8 rows is sent as up to
+             * 14 rows, i.e., 6 additional rows, each with a filter byte
+             * and possibly a padding byte
+             */
+            if (png_ptr->interlaced)
+               uncompressed_idat_size += ((png_ptr->height + 7)/8) *
+                   (png_ptr->bit_depth < 8 ? 12 : 6);
+
             unsigned int z_cinfo = z_cmf >> 4;
             unsigned int half_z_window_size = 1 << (z_cinfo + 7);
             while (uncompressed_idat_size <= half_z_window_size &&