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>
This commit is contained in:
Ganesh Ajjanagadde 2015-10-27 20:11:40 -04:00
parent e8e7eb150f
commit 20a30077c3
1 changed files with 4 additions and 3 deletions

View File

@ -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);