[libpng17 Updated the documentation about CRC and ADLER32 handling.

4 files changed, 14 insertions, 4 deletions

diff --git a/ANNOUNCE b/ANNOUNCE
index 320070fb8..c7f907924 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1409,6 +1409,7 @@ Version 1.7.0beta84 [September 26, 2016]
   Add tests/badcrc.png and tests/badadler.png to tests/pngtest.
 
 Version 1.7.0beta85 [September 26, 2016]
+  Updated the documentation about CRC and ADLER32 handling.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
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diff --git a/CHANGES b/CHANGES
index 8509f8cd9..55535a33a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5709,6 +5709,7 @@ Version 1.7.0beta84 [September 26, 2016]
   Add tests/badcrc.png and tests/badadler.png to tests/pngtest.
 
 Version 1.7.0beta85 [September 26, 2016]
+  Updated the documentation about CRC and ADLER32 handling.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/libpng-manual.txt b/libpng-manual.txt
index 6d914d304..a9aa0fc62 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -471,8 +471,9 @@ the default, use
 
 The values for png_set_crc_action() say how libpng is to handle CRC errors in
 ancillary and critical chunks, and whether to use the data contained
-therein.  Note that it is impossible to "discard" data in a critical
-chunk.
+therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
+is handled while reading the IDAT chunk. Note that it is impossible to
+"discard" data in a critical chunk.
 
 Choices for (int) crit_action are
    PNG_CRC_DEFAULT      0  error/quit
@@ -489,6 +490,9 @@ Choices for (int) ancil_action are
    PNG_CRC_QUIET_USE    4  quiet/use data
    PNG_CRC_NO_CHANGE    5  use the current value
 
+When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
+checksums are not only ignored, but they are not evaluated.
+
 Setting up callback code
 
 You can set up a callback function to handle any unknown chunks in the
diff --git a/libpng.3 b/libpng.3
index 03873a11f..22eb58ecc 100644
--- a/libpng.3
+++ b/libpng.3
@@ -971,8 +971,9 @@ the default, use
 
 The values for png_set_crc_action() say how libpng is to handle CRC errors in
 ancillary and critical chunks, and whether to use the data contained
-therein.  Note that it is impossible to "discard" data in a critical
-chunk.
+therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
+is handled while reading the IDAT chunk. Note that it is impossible to
+"discard" data in a critical chunk.
 
 Choices for (int) crit_action are
    PNG_CRC_DEFAULT      0  error/quit
@@ -989,6 +990,9 @@ Choices for (int) ancil_action are
    PNG_CRC_QUIET_USE    4  quiet/use data
    PNG_CRC_NO_CHANGE    5  use the current value
 
+When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
+checksums are not only ignored, but they are not evaluated.
+
 .SS Setting up callback code
 
 You can set up a callback function to handle any unknown chunks in the