On Tue, 27 Aug 2024, Rémi Denis-Courmont wrote:
Le 27 août 2024 03:03:37 GMT+03:00, Marton Balint <c...@passwd.hu> a écrit :
Using INFINITY can cause issues with -ffast-math, and since we only use this
value to decide the formatting, we can just as easily use 0 for log10 of zero.
FFmpeg does not enable fast-math and last I tried it won't work at all anyway:
FATE commits seppuku by OoM.
The statement above is completely false if applied to the whole code
base rather than just this function. Notably FFMAX and FFMIN behave
differently under -fno-infinite-math (which is implied by -ffast-math).
I meant the statement to the code in question, not generically.
I suspect that *this* code is just the tip of the iceberg. It's not hard
to imagine that ignoring infinities will break stuff, for one: reading
raw binary content as float can lead to infinities and other NaNs.
Agreed.
So IMO this patch is wrong. Either we've audited the whole code base,
and then we should enable -ffast-math, or at least -fno-infinite-math by
default, or we haven't and then we should not be papering over the issue
like this.
IMHO the patch itself is harmless (simple, easy to follow), and if it
helps somebody (no matter how unupported its use-case is), then why the
hell not. But I can understand your point of view, that we should not
bother with it, if it is unsupported in the first place, so I will just
drop this, did not feel strongly about it anyway.
Regards,
Marton
Signed-off-by: Marton Balint <c...@passwd.hu>
---
libavutil/timestamp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libavutil/timestamp.c b/libavutil/timestamp.c
index 6c231a517d..be4540d4c8 100644
--- a/libavutil/timestamp.c
+++ b/libavutil/timestamp.c
@@ -24,7 +24,7 @@ char *av_ts_make_time_string2(char *buf, int64_t ts,
AVRational tb)
snprintf(buf, AV_TS_MAX_STRING_SIZE, "NOPTS");
} else {
double val = av_q2d(tb) * ts;
- double log = (fpclassify(val) == FP_ZERO ? -INFINITY :
floor(log10(fabs(val))));
+ double log = (fpclassify(val) == FP_ZERO ? 0 :
floor(log10(fabs(val))));
int precision = (isfinite(log) && log < 0) ? -log + 5 : 6;
int last = snprintf(buf, AV_TS_MAX_STRING_SIZE, "%.*f", precision, val);
last = FFMIN(last, AV_TS_MAX_STRING_SIZE - 1) - 1;
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