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| author | Joseph Myers <joseph@codesourcery.com> | 2015-02-26 15:13:22 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-02-26 15:14:58 +0000 |
| commit | 380bd0fd2418f8988217de950f8b8ff18af0cb2b (patch) | |
| tree | abb55a322fc5e1b829761d91a23510ecfc6bf1ee /sysdeps/ieee754 | |
| parent | 4a28f4d55a6cc33474c0792fe93b5942d81bf185 (diff) | |
| download | glibc-380bd0fd2418f8988217de950f8b8ff18af0cb2b.zip glibc-380bd0fd2418f8988217de950f8b8ff18af0cb2b.tar.gz glibc-380bd0fd2418f8988217de950f8b8ff18af0cb2b.tar.bz2 | |
Fix ldbl-128ibm logbl near powers of 2 (bug 18030).
The ldbl-128ibm implementation of logbl produces incorrect results
when the high part of the argument is a power of 2 and the low part a
nonzero number with the opposite sign (and so the returned exponent
should be 1 less than that of the high part). For example, logbl
(0x1.ffffffffffffffp1L) returns 2 but should return 1. (This is
similar to (fixed) bug 16740 for frexpl, and (fixed) bug 18029 for
ilogbl.) This patch adds checks for that case.
Tested for powerpc.
[BZ #18030]
* sysdeps/ieee754/ldbl-128ibm/s_logbl.c (__logbl): Adjust exponent
of power of 2 down when low part has opposite sign.
* math/libm-test.inc (logb_test_data): Add more tests.
Diffstat (limited to 'sysdeps/ieee754')
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/s_logbl.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c index dbd3478..22e5fc2 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c @@ -26,11 +26,12 @@ long double __logbl (long double x) { - int64_t hx, rhx; - double xhi; + int64_t hx, hxs, rhx; + double xhi, xlo; - xhi = ldbl_high (x); + ldbl_unpack (x, &xhi, &xlo); EXTRACT_WORDS64 (hx, xhi); + hxs = hx; hx &= 0x7fffffffffffffffLL; /* high |x| */ if (hx == 0) return -1.0 / fabs (x); @@ -42,6 +43,16 @@ __logbl (long double x) though it were normalized. */ rhx -= __builtin_clzll (hx) - 12; } + else if ((hx & 0x000fffffffffffffLL) == 0) + { + /* If the high part is a power of 2, and the low part is nonzero + with the opposite sign, the low part affects the + exponent. */ + int64_t lx; + EXTRACT_WORDS64 (lx, xlo); + if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0) + rhx--; + } return (long double) (rhx - 1023); } #ifndef __logbl |