| Message ID | 8f249510-5072-c2b1-a996-a059264da80c@CoSoCo.de |
|---|---|
| State | New |
| Headers | show |
> -----Original Message----- > From: ffmpeg-devel [mailto:ffmpeg-devel-bounces@ffmpeg.org] On Behalf > Of Ulf Zibis > Sent: Wednesday, July 17, 2019 2:34 PM > To: ffmpeg-devel@ffmpeg.org > Subject: Re: [FFmpeg-devel] [PATCH v1] Bug #8027 - Wrong result for > FFSIGN(0) > > Again with the patch attached ... > > Am 17.07.19 um 08:30 schrieb Ulf Zibis: > > Hi, > > > > I have a patch for bug #8027 <https://trac.ffmpeg.org/ticket/8027> (see > > attachment). Why do you think FFSIGN(0.0) should return +1? What issue do you meet? I think the value of FFSIGN(0) depends on how we define the behavior of FFSIGN(). Thanks! Ruiling > > > > But there is still a problem with -0.0, but FFABS(-0.0) works fine. > > > > Testcode: > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(0): %d\n", FFSIGN(0)); > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(-0): %d\n", FFSIGN(-0)); > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(0.0D): %d\n", FFSIGN(0.0D)); > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(-0.0D): %d\n", FFSIGN(-0.0D)); > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(-0.0F): %d\n", FFSIGN(-0.0F)); > > av_log(NULL, AV_LOG_ERROR, "FFSIGN(-0.0): %d\n", FFSIGN(-0.0)); > > > > av_log(NULL, AV_LOG_ERROR, "FFABS(0): %d\n", FFABS(0)); > > av_log(NULL, AV_LOG_ERROR, "FFABS(-0): %d\n", FFABS(-0)); > > av_log(NULL, AV_LOG_ERROR, "FFABS(0.0D): %f\n", FFABS(0.0D)); > > av_log(NULL, AV_LOG_ERROR, "FFABS(-0.0D): %f\n", FFABS(-0.0D)); > > av_log(NULL, AV_LOG_ERROR, "FFABS(-0.0F): %f\n", FFABS(-0.0F)); > > av_log(NULL, AV_LOG_ERROR, "FFABS(-0.0): %f\n", FFABS(-0.0)); > > > > Results: > > FFSIGN(0): 1 > > FFSIGN(-0): 1 > > FFSIGN(0.0D): 1 > > FFSIGN(-0.0D): 1 > > FFSIGN(-0.0F): 1 > > FFSIGN(-0.0): 1 > > FFABS(0): 0 > > FFABS(-0): 0 > > FFABS(0.0D): 0.000000 > > FFABS(-0.0D): -0.000000 > > FFABS(-0.0F): -0.000000 > > FFABS(-0.0): -0.000000 > > > > -Ulf > > > > _______________________________________________ > > ffmpeg-devel mailing list > > ffmpeg-devel@ffmpeg.org > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > > > To unsubscribe, visit link above, or email > > ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
Am 17.07.19 um 08:57 schrieb Song, Ruiling: > Why do you think FFSIGN(0.0) should return +1? Because anyone I ask including mathematicians, is the opinion that the sign of 0 is positive. > What issue do you meet? I wanted to use the macro in my code, but with the current behaviour it is worthless. -Ulf
On 7/17/19, Ulf Zibis <Ulf.Zibis@cosoco.de> wrote: > > Am 17.07.19 um 08:57 schrieb Song, Ruiling: >> Why do you think FFSIGN(0.0) should return +1? > Because anyone I ask including mathematicians, is the opinion that the > sign of 0 is positive. > >> What issue do you meet? > > I wanted to use the macro in my code, but with the current behaviour it > is worthless. Use copysign(f), see relevant manual page for documentation of this function. Also, you always can add own macro, in local to your developed filter. > > -Ulf > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
On Wed, Jul 17, 2019 at 9:55 AM Ulf Zibis <Ulf.Zibis@cosoco.de> wrote: > > > Am 17.07.19 um 08:57 schrieb Song, Ruiling: > > Why do you think FFSIGN(0.0) should return +1? > Because anyone I ask including mathematicians, is the opinion that the > sign of 0 is positive. It really doesn't matter what anyone else thinks, the macro was defined the way it is, and changing it now has a chance of breaking random places that rely on the current behavior. > > > What issue do you meet? > > I wanted to use the macro in my code, but with the current behaviour it > is worthless. > Any macro starting with FF is technically internal to FFmpeg and should not be relied upon by external software. Furthermore, this macro is so extremely simple, you can just make your own with no overhead or issues, if this one does not suit your needs. - Hendrik
Ulf Zibis (12019-07-17): > Because anyone I ask including mathematicians, is the opinion that the > sign of 0 is positive. They were not very competent mathematicians. Regards,
Am 17.07.19 um 19:21 schrieb Nicolas George: > Ulf Zibis (12019-07-17): >> Because anyone I ask including mathematicians, is the opinion that the >> sign of 0 is positive. > They were not very competent mathematicians. In normal arithmetic, yes, sgn(0) is 0, but here we are in floating point arithmetics where sgn(0) is 1, see: https://en.wikipedia.org/wiki/Floating-point_arithmetic#Signed_zero But FFSIGN(0) results as -1, which is never correct. -Ulf
Am 17.07.19 um 10:12 schrieb Hendrik Leppkes: > ..., the macro was defined the way it is, and changing it now has a > chance of breaking > random places that rely on the current behavior. OK, that would be risky. Maybe we could add another macro FFSGN. Then maintainers of individual code parts could check the usage over the time. #define FFSGN(a) ((a) > 0 ? 1 : (a) < 0 ? -1 : 0) -Ulf
Ulf Zibis (12019-07-18): > Maybe we could add another macro FFSGN. Then maintainers of individual > code parts could check the usage over the time. Or maybe write robust code that does not need that kind of hair splitting. Regards,
On Thu, Jul 18, 2019 at 9:17 PM Ulf Zibis <Ulf.Zibis@cosoco.de> wrote: > > > Am 17.07.19 um 10:12 schrieb Hendrik Leppkes: > > ..., the macro was defined the way it is, and changing it now has a > > chance of breaking > > random places that rely on the current behavior. > > OK, that would be risky. > > Maybe we could add another macro FFSGN. Then maintainers of individual > code parts could check the usage over the time. > > #define FFSGN(a) ((a) > 0 ? 1 : (a) < 0 ? -1 : 0) > Unless something inside FFmpeg needs such a behavior, that is unlikely. - Hendrik
From aa27ca089dafb3bc2f2c5aaa171856b235989ea4 Mon Sep 17 00:00:00 2001 From: Ulf Zibis <Ulf.Zibis@CoSoCo.de> Date: 16.07.2019, 23:36:51 avutil/common.h: Correct result for FFSIGN(0.0) diff --git a/libavutil/common.h b/libavutil/common.h index 8db0291..4b14e7b 100644 --- a/libavutil/common.h +++ b/libavutil/common.h @@ -70,7 +70,7 @@ * @see FFNABS() */ #define FFABS(a) ((a) >= 0 ? (a) : (-(a))) -#define FFSIGN(a) ((a) > 0 ? 1 : -1) +#define FFSIGN(a) ((a) >= 0 ? 1 : -1) /** * Negative Absolute value.