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author | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-10-27 20:11:40 -0400 |
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committer | Ganesh Ajjanagadde <gajjanagadde@gmail.com> | 2015-10-30 13:42:04 -0400 |
commit | 20a30077c3659e6dc0c5b9dfa08d39b70a6b5f4e (patch) | |
tree | 60278cfb15cdcf5e0556270f50cbfd3aba56dfbd /libavutil | |
parent | e8e7eb150f152c9e4858ef0be3e76e4f98533cf6 (diff) | |
download | ffmpeg-streaming-20a30077c3659e6dc0c5b9dfa08d39b70a6b5f4e.zip ffmpeg-streaming-20a30077c3659e6dc0c5b9dfa08d39b70a6b5f4e.tar.gz |
avutil/mathematics: correct documentation for av_gcd
av_gcd is now always defined regardless of input. This documents this
change in the "documented API". Two benefits (closely related):
1. The function is robust, and there is no need to worry about INT64_MIN, etc.
2. Clients of av_gcd, like av_reduce, can now be made fully correct. Currently,
av_reduce can trigger undefined behavior if e.g num is INT64_MIN due to
integer overflow in the FFABS. Furthermore, this undefined behavior is
completely undocumented, and could be a fuzzer's paradise. The FFABS was needed in the past as
av_gcd was undefined for negative inputs. In order to make av_reduce
robust, it is essential to guarantee that av_gcd works for all int64_t.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
Diffstat (limited to 'libavutil')
-rw-r--r-- | libavutil/mathematics.h | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/libavutil/mathematics.h b/libavutil/mathematics.h index ac94488..57c44f8 100644 --- a/libavutil/mathematics.h +++ b/libavutil/mathematics.h @@ -77,9 +77,10 @@ enum AVRounding { }; /** - * Return the greatest common divisor of a and b. - * If both a and b are 0 or either or both are <0 then behavior is - * undefined. + * Compute the greatest common divisor of a and b. + * + * @return gcd of a and b up to sign; if a >= 0 and b >= 0, return value is >= 0; + * if a == 0 and b == 0, returns 0. */ int64_t av_const av_gcd(int64_t a, int64_t b); |