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* [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64
@ 2013-06-03 16:05 carlos at redhat dot com
2013-06-03 16:06 ` [Bug math/15563] " carlos at redhat dot com
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: carlos at redhat dot com @ 2013-06-03 16:05 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15563
Bug ID: 15563
Summary: sincos() is incorrect for long double and large inputs
on x86_64
Product: glibc
Version: 2.18
Status: NEW
Keywords: glibc_2.15
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: carlos at redhat dot com
CC: aj at suse dot de, bugdal at aerifal dot cx, carlos at redhat dot com,
ppluzhnikov at google dot com, vincent-srcware at vinc17 dot net
Depends on: 13658
Blocks: 13851, 13852, 13854
Still broken for long double on x86/x86_64.
Tested with current sources.
+++ This bug was initially created as a clone of Bug #13658 +++
sincos() is inaccurate for large inputs on x86_64: with glibc 2.13,
#define _GNU_SOURCE
#include <stdio.h>
#include <math.h>
int main (void)
{
volatile double x = 1.0e22;
double s1, s2, c1;
sincos (x, &s1, &c1);
s2 = sin (x);
printf ("s1 = %.17g\n", s1);
printf ("s2 = %.17g\n", s2);
return 0;
}
outputs:
s1 = 0.46261304076460175
s2 = -0.85220084976718879
(s2 is the correct value). I suppose that contrary to the other trig functions,
glibc uses the hardware sincos instruction, which has never been meant to be
used directly by a C library (the hardware elementary functions of the x86
processors were designed for small inputs, and they must not be used by code
where inputs can be large, like here). The sincos() function can simply be
implemented by a call to sin() and a call to cos() on this target.
Ditto for sincosf() and sincosl().
Note: x86 (32 bits) has the same problem, but it has been claimed that users
don't care about correctness on this target.
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* [Bug math/15563] sincos() is incorrect for long double and large inputs on x86_64
2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
@ 2013-06-03 16:06 ` carlos at redhat dot com
2013-06-03 17:01 ` joseph at codesourcery dot com
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: carlos at redhat dot com @ 2013-06-03 16:06 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15563
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|glibc_2.15 |
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* [Bug math/15563] sincos() is incorrect for long double and large inputs on x86_64
2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
2013-06-03 16:06 ` [Bug math/15563] " carlos at redhat dot com
@ 2013-06-03 17:01 ` joseph at codesourcery dot com
2013-06-03 17:47 ` carlos at redhat dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: joseph at codesourcery dot com @ 2013-06-03 17:01 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15563
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
I can't tell what you think the bug is here. You give a testcase for
double but talk about long double, and with the obvious substitutions
#define _GNU_SOURCE
#include <stdio.h>
#include <math.h>
int main (void)
{
volatile long double x = 1.0e22;
long double s1, s2, c1;
sincosl (x, &s1, &c1);
s2 = sinl (x);
printf ("s1 = %.17Lg\n", s1);
printf ("s2 = %.17Lg\n", s2);
return 0;
}
I get on x86_64 (with current glibc)
s1 = -0.8522008497671888
s2 = -0.8522008497671888
which appears to be what you'd expect. So what program are you building,
with what options, and running with current glibc, and getting what
results, and what would you like instead?
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* [Bug math/15563] sincos() is incorrect for long double and large inputs on x86_64
2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
2013-06-03 16:06 ` [Bug math/15563] " carlos at redhat dot com
2013-06-03 17:01 ` joseph at codesourcery dot com
@ 2013-06-03 17:47 ` carlos at redhat dot com
2013-06-03 19:01 ` joseph at codesourcery dot com
2014-06-13 17:32 ` fweimer at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: carlos at redhat dot com @ 2013-06-03 17:47 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15563
Carlos O'Donell <carlos at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #2 from Carlos O'Donell <carlos at redhat dot com> ---
(In reply to joseph@codesourcery.com from comment #1)
> I can't tell what you think the bug is here. You give a testcase for
> double but talk about long double, and with the obvious substitutions
I hadn't seen and could not find any discussion of this fix for long double
(remember at the time ldbl-96 did not correctly do argument reduction).
The additional test case I was using was:
cat >> test.c <<EOF
#include <stdio.h>
#include <math.h>
int main() {
long double x;
for (x=1.0;x<1.e38;x*=2.0)
printf("%Le %Lf\n",x,sinl(x));
return 0;
}
EOF
gcc -Wall -pedantic
-Wl,-rpath=/home/carlos/build/glibc:/home/carlos/build/glibc/math
-Wl,--dynamic-linker=/home/carlos/build/glibc/elf/ld.so -o test test.c -lm
Producing the following results for long double on x86-64 with master:
1.000000e+00 0.841471
2.000000e+00 0.909297
4.000000e+00 -0.756802
8.000000e+00 0.989358
1.600000e+01 -0.287903
3.200000e+01 0.551427
6.400000e+01 0.920026
1.280000e+02 0.721038
2.560000e+02 -0.999208
5.120000e+02 0.079518
1.024000e+03 -0.158533
2.048000e+03 -0.313057
4.096000e+03 -0.594642
8.192000e+03 -0.956173
1.638400e+04 -0.559938
3.276800e+04 0.927856
6.553600e+04 0.692065
1.310720e+05 -0.999114
2.621440e+05 -0.084107
5.242880e+05 0.167618
1.048576e+06 0.330493
2.097152e+06 0.623844
4.194304e+06 0.975129
8.388608e+06 0.432248
1.677722e+07 -0.779564
3.355443e+07 -0.976517
6.710886e+07 0.420760
1.342177e+08 -0.763403
2.684355e+08 -0.986198
5.368709e+08 0.326568
1.073742e+09 -0.617326
2.147484e+09 -0.971310
4.294967e+09 -0.461987
8.589935e+09 0.819460
1.717987e+10 0.939325
3.435974e+10 -0.644430
6.871948e+10 0.985544
1.374390e+11 0.333940
2.748779e+11 -0.629540
5.497558e+11 -0.978265
1.099512e+12 -0.405705
2.199023e+12 0.741632
4.398047e+12 0.994984
8.796093e+12 -0.199069
1.759219e+13 0.390169
3.518437e+13 0.718491
7.036874e+13 0.999473
1.407375e+14 -0.064885
2.814750e+14 0.129496
5.629500e+14 0.256811
1.125900e+15 0.496397
2.251800e+15 0.861840
4.503600e+15 0.874217
9.007199e+15 -0.848926
1.801440e+16 0.897335
3.602880e+16 -0.792078
7.205759e+16 0.967000
1.441152e+17 -0.492738
2.882304e+17 0.857539
5.764608e+17 0.882269
1.152922e+18 -0.830649
2.305843e+18 0.925004
4.611686e+18 -0.702922
9.223372e+18 0.999930
1.844674e+19 0.023599
3.689349e+19 -0.047184
7.378698e+19 -0.094263
1.475740e+20 -0.187686
2.951479e+20 -0.368701
5.902958e+20 -0.685451
1.180592e+21 -0.998179
2.361183e+21 -0.120410
4.722366e+21 0.239068
9.444733e+21 0.464271
1.888947e+22 0.822404
3.777893e+22 0.935738
7.555786e+22 -0.660063
1.511157e+23 0.991692
3.022315e+23 0.255132
6.044629e+23 -0.493378
1.208926e+24 -0.858295
2.417852e+24 -0.880879
4.835703e+24 0.833914
9.671407e+24 -0.920465
1.934281e+25 0.719481
3.868563e+25 -0.999377
7.737125e+25 0.070569
1.547425e+26 -0.140786
3.094850e+26 -0.278768
6.189700e+26 -0.535435
1.237940e+27 -0.904431
2.475880e+27 -0.771696
4.951760e+27 0.981584
9.903520e+27 -0.375022
1.980704e+28 0.695303
3.961408e+28 0.999452
7.922816e+28 0.066180
1.584563e+29 -0.132069
3.169127e+29 -0.261824
6.338253e+29 -0.505382
1.267651e+30 -0.872184
2.535301e+30 -0.853307
5.070602e+30 0.889843
1.014120e+31 -0.812011
2.028241e+31 0.947848
4.056482e+31 -0.604204
8.112964e+31 0.962895
1.622593e+32 0.519724
3.245186e+32 -0.888036
6.490371e+32 -0.816591
1.298074e+33 0.942700
2.596148e+33 -0.629050
5.192297e+33 0.978003
1.038459e+34 0.408007
2.076919e+34 -0.745003
4.153837e+34 -0.993925
8.307675e+34 0.218781
1.661535e+35 -0.426961
3.323070e+35 -0.772176
6.646140e+35 -0.981295
1.329228e+36 0.377820
2.658456e+36 -0.699631
5.316912e+36 -0.999779
1.063382e+37 -0.042054
2.126765e+37 0.084034
4.253530e+37 0.167473
8.507059e+37 0.330216
This looks perfectly correct, and therefore it seems I must have made a mistake
in my initial testing.
I will note that this is not fixed in 2.15, but is fixed on master.
I haven't done a thorough check to find which patch fixed this.
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* [Bug math/15563] sincos() is incorrect for long double and large inputs on x86_64
2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
` (2 preceding siblings ...)
2013-06-03 17:47 ` carlos at redhat dot com
@ 2013-06-03 19:01 ` joseph at codesourcery dot com
2014-06-13 17:32 ` fweimer at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: joseph at codesourcery dot com @ 2013-06-03 19:01 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=15563
--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
commit 8848d99dce1e57168a492d146f5e72195c7665a5
Author: Joseph Myers <joseph@codesourcery.com>
Date: Fri Mar 16 12:28:25 2012 +0000
Implement ldbl-96 sinl / cosl / sincosl (bug 13851).
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* [Bug math/15563] sincos() is incorrect for long double and large inputs on x86_64
2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
` (3 preceding siblings ...)
2013-06-03 19:01 ` joseph at codesourcery dot com
@ 2014-06-13 17:32 ` fweimer at redhat dot com
4 siblings, 0 replies; 6+ messages in thread
From: fweimer at redhat dot com @ 2014-06-13 17:32 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=15563
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2013-06-03 16:05 [Bug math/15563] New: sincos() is incorrect for long double and large inputs on x86_64 carlos at redhat dot com
2013-06-03 16:06 ` [Bug math/15563] " carlos at redhat dot com
2013-06-03 17:01 ` joseph at codesourcery dot com
2013-06-03 17:47 ` carlos at redhat dot com
2013-06-03 19:01 ` joseph at codesourcery dot com
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