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| author | Joseph Myers <joseph@codesourcery.com> | 2016-06-14 16:41:50 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2016-06-14 16:41:50 +0000 |
| commit | 228a78c21b9ed27004a1ccb5bd48a3263d7cd67d (patch) | |
| tree | b15d7ef485701903f1fe3e79d7c044137ec2fbb4 /math | |
| parent | f4015c8a861803c128112ca41fc62817398bd1c0 (diff) | |
| download | glibc-228a78c21b9ed27004a1ccb5bd48a3263d7cd67d.tar.gz glibc-228a78c21b9ed27004a1ccb5bd48a3263d7cd67d.tar.xz glibc-228a78c21b9ed27004a1ccb5bd48a3263d7cd67d.zip | |
Fix i386 fdim double rounding (bug 20255).
fdim suffers from double rounding on i386 because subtracting two double values can produce an inexact long double value exactly half way between two double values. This patch fixes this by creating an i386-specific version of fdim - C, based on the generic version, unlike the previous .S version - which sets the x87 precision control to double precision for the subtraction and then restores it afterwards. As noted in the comment added, there are no issues of double rounding for subnormals (a case that setting precision control does not address) because subtraction cannot produce an inexact result in the subnormal range. Tested for x86_64 and x86. [BZ #20255] * sysdeps/i386/fpu/s_fdim.c: New file. Based on math/s_fdim.c. * math/libm-test.inc (fdim_test_data): Add another test.
Diffstat (limited to 'math')
| -rw-r--r-- | math/libm-test.inc | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/math/libm-test.inc b/math/libm-test.inc index cc41c63e7a..d6cad6634c 100644 --- a/math/libm-test.inc +++ b/math/libm-test.inc @@ -7203,6 +7203,9 @@ static const struct test_ff_f_data fdim_test_data[] = TEST_ff_f (fdim, 0, 9, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fdim, -9, 0, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fdim, 0, -9, 9, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), +#if TEST_COND_binary64 + TEST_ff_f (fdim, 1.0, -0x1.0000000000001p-53, 1.0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 0x1.0000000000001p0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 1.0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 0x1.0000000000001p0, INEXACT_EXCEPTION|ERRNO_UNCHANGED), +#endif TEST_ff_f (fdim, min_subnorm_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fdim, -min_subnorm_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), TEST_ff_f (fdim, min_subnorm_value, -min_subnorm_value, 2*min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED), |