Attachment 135251 Details for Bug 101033 – 0001-nsSBCSGroupProber.cpp-accound-to-FPU-imprecision.patch

[patch] 0001-nsSBCSGroupProber.cpp-accound-to-FPU-imprecision.patch

0001-nsSBCSGroupProber.cpp-accound-to-FPU-imprecision.patch (text/plain), 1.71 KB, created by Sergei Trofimovich on 2017-11-05 23:05:02 UTC

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Creator: Sergei Trofimovich

Created: 2017-11-05 23:05:02 UTC

Size: 1.71 KB

patch

obsolete

>From cfbab07631225ca025ec9f2a3f8982b13b6a76a3 Mon Sep 17 00:00:00 2001
>From: Sergei Trofimovich <slyfox@gentoo.org>
>Date: Sun, 5 Nov 2017 22:54:28 +0000
>Subject: [PATCH] nsSBCSGroupProber.cpp: accound to FPU imprecision
>
>For (pseudo-)code like
>    max([1.01, 1.01, 1.01])
>real FPU hardware does not guarantee stable output.
>
>For example on 387 FPU internal precision is 80 bits
>thus loading/storing from 80-bit register into 32-bit
>memory slot slightly changes value of computation:
>    https://gcc.gnu.org/wiki/x87note
>(note other hardware can deviate from IEEE-754 either
>by construction or being in certain modes)
>
>This change accounts for minor value deviation by picking
>not necessarily biggest vaue but the one that is far enough
>from previous value (> FLT_EPSILON).
>
>Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
>---
> src/nsSBCSGroupProber.cpp | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
>diff --git a/src/nsSBCSGroupProber.cpp b/src/nsSBCSGroupProber.cpp
>index f956d25..c2dd33f 100644
>--- a/src/nsSBCSGroupProber.cpp
>+++ b/src/nsSBCSGroupProber.cpp
>@@ -36,6 +36,7 @@
>  *
>  * ***** END LICENSE BLOCK ***** */
> 
>+#include <float.h>
> #include <stdio.h>
> #include "prmem.h"
> 
>@@ -301,7 +302,11 @@ float nsSBCSGroupProber::GetConfidence(void)
>       if (!mIsActive[i])
>         continue;
>       cf = mProbers[i]->GetConfidence();
>-      if (bestConf < cf)
>+      // make sure the difference is more fhan FPU noise
>+      // to make max() stable. See the discusstion at:
>+      //    https://bugs.freedesktop.org/show_bug.cgi?id=101033
>+      //    https://github.com/gentoo/gentoo/pull/5993#issuecomment-338335710
>+      if (cf - bestConf > FLT_EPSILON)
>       {
>         bestConf = cf;
>         mBestGuess = i;
>-- 
>2.15.0
>

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