diff options
| author | Joseph Myers <joseph@codesourcery.com> | 2017-03-15 22:00:54 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2017-03-15 22:00:54 +0000 |
| commit | e4e52ff059f46472145433d2bd003d5383f89e82 (patch) | |
| tree | c5044e3b2e2f98778087319e79d308bd817e9a75 /sysdeps | |
| parent | 5d20a49aaccef5ef7adac93d5ca159f6b7ba0105 (diff) | |
| download | glibc-e4e52ff059f46472145433d2bd003d5383f89e82.tar.gz glibc-e4e52ff059f46472145433d2bd003d5383f89e82.tar.xz glibc-e4e52ff059f46472145433d2bd003d5383f89e82.zip | |
Improve float range reduction accuracy near pi/2 (bug 21094).
Bug 21094 reports 3ulp errors of cosf and tanf for certain arguments near pi/2 arising from the use of an insufficiently accurate range reduction. (To be clear, this is a quality-of-implementation issue relating to the apparent intent of those particular cosf and tanf implementations; 3ulp is within the general glibc accuracy goals, so not inherently a bug.) This patch fixes that error by making a wider range of cases use the existing more accurate range reduction for arguments close to pi/2. The wider range of values is still narrow enough for the "z -= pio2_2;" in the more accurate case to be exact, as the code expects. Tested for x86_64, x86 and mips64; no ulps updates needed (but at least on mips64, the larger ulps were seen if the tests were added without the substantive fix). [BZ #21094] * sysdeps/ieee754/flt-32/e_rem_pio2f.c (__ieee754_rem_pio2f): Use 24+24+24-bit pi for wider range of values around pi/2. * math/auto-libm-test-in: Add more tests of cos and tan. * math/auto-libm-test-out-cos: Regenerated. * math/auto-libm-test-out-tan: Likewise.
Diffstat (limited to 'sysdeps')
| -rw-r--r-- | sysdeps/ieee754/flt-32/e_rem_pio2f.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/sysdeps/ieee754/flt-32/e_rem_pio2f.c b/sysdeps/ieee754/flt-32/e_rem_pio2f.c index 0928373498..c4d28c8657 100644 --- a/sysdeps/ieee754/flt-32/e_rem_pio2f.c +++ b/sysdeps/ieee754/flt-32/e_rem_pio2f.c @@ -100,7 +100,7 @@ int32_t __ieee754_rem_pio2f(float x, float *y) if(ix<0x4016cbe4) { /* |x| < 3pi/4, special case with n=+-1 */ if(hx>0) { z = x - pio2_1; - if((ix&0xfffffff0)!=0x3fc90fd0) { /* 24+24 bit pi OK */ + if((ix&0xffffffc0)!=0x3fc90fc0) { /* 24+24 bit pi OK */ y[0] = z - pio2_1t; y[1] = (z-y[0])-pio2_1t; } else { /* near pi/2, use 24+24+24 bit pi */ @@ -111,7 +111,7 @@ int32_t __ieee754_rem_pio2f(float x, float *y) return 1; } else { /* negative x */ z = x + pio2_1; - if((ix&0xfffffff0)!=0x3fc90fd0) { /* 24+24 bit pi OK */ + if((ix&0xffffffc0)!=0x3fc90fc0) { /* 24+24 bit pi OK */ y[0] = z + pio2_1t; y[1] = (z-y[0])+pio2_1t; } else { /* near pi/2, use 24+24+24 bit pi */ |