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| author | Joseph Myers <joseph@codesourcery.com> | 2013-12-19 13:36:10 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2013-12-19 13:36:10 +0000 |
| commit | f88acd39da2a509081e541b84ecbf204ef20f9e8 (patch) | |
| tree | 383c0bcce4b3e74c9150d01550e7c412e47981bd /sysdeps/i386/fpu/e_expl.S | |
| parent | c688b4196014e0162a1ff11120f6c9516be0c6cb (diff) | |
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Fix x86/x86_64 expm1 inaccuracy near 0 in directed rounding modes (bug 16293).
Bug 16293 is inaccuracy of x86/x86_64 versions of expm1, near 0 in
directed rounding modes, that arises from frndint rounding the
exponent to 1 or -1 instead of 0, resulting in large cancellation
error. This inaccuracy in turn affects other functions such as sinh
that use expm1. This patch fixes the problem by setting
round-to-nearest mode temporarily around the affected calls to
frndint. I don't think this is needed for other uses of frndint, such
as in exp itself, as only for expm1 is the cancellation error
significant.
Tested x86_64 and x86 and ulps updated accordingly.
* sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Set
round-to-nearest mode when using frndint.
* sysdeps/i386/fpu/s_expm1.S (__expm1): Likewise.
* sysdeps/i386/fpu/s_expm1f.S (__expm1f): Likewise.
* sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
Likewise.
* math/auto-libm-test-in: Add more tests of expm1. Do not expect
sinh test to fail.
* math/auto-libm-test-out: Regenerated.
* math/libm-test.inc (TEST_COND_x86_64): Remove macro.
(TEST_COND_x86): Likewise.
(expm1_tonearest_test_data): New array.
(expm1_test_tonearest): New function.
(expm1_towardzero_test_data): New array.
(expm1_test_towardzero): New function.
(expm1_downward_test_data): New array.
(expm1_test_downward): New function.
(expm1_upward_test_data): New array.
(expm1_test_upward): New function.
(main): Run the new test functions.
* sysdeps/i386/fpu/libm-test-ulps: Update.
* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
Diffstat (limited to 'sysdeps/i386/fpu/e_expl.S')
| -rw-r--r-- | sysdeps/i386/fpu/e_expl.S | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/sysdeps/i386/fpu/e_expl.S b/sysdeps/i386/fpu/e_expl.S index af339f0ff4..a8a5e70b07 100644 --- a/sysdeps/i386/fpu/e_expl.S +++ b/sysdeps/i386/fpu/e_expl.S @@ -130,9 +130,24 @@ ENTRY(IEEE754_EXPL) #endif 3: FLDLOG /* 1 log2(base) */ fmul %st(1), %st /* 1 x log2(base) */ +#ifdef USE_AS_EXPM1L + /* Set round-to-nearest temporarily. */ + subl $8, %esp + cfi_adjust_cfa_offset (8) + fstcw 4(%esp) + movl $0xf3ff, %edx + andl 4(%esp), %edx + movl %edx, (%esp) + fldcw (%esp) +#endif frndint /* 1 i */ fld %st(1) /* 2 x */ frndint /* 2 xi */ +#ifdef USE_AS_EXPM1L + fldcw 4(%esp) + addl $8, %esp + cfi_adjust_cfa_offset (-8) +#endif fld %st(1) /* 3 i */ fldt MO(c0) /* 4 c0 */ fld %st(2) /* 5 xi */ |