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| author | Joseph Myers <joseph@codesourcery.com> | 2015-02-26 12:57:21 +0000 |
|---|---|---|
| committer | Joseph Myers <joseph@codesourcery.com> | 2015-02-26 12:57:21 +0000 |
| commit | 524ae9ea2e3ae9f5bf5d655595fda827e9dc50a1 (patch) | |
| tree | 363ab7a9bab473dc18c22b1179d8b549d8497f80 /sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c | |
| parent | 23d43090e0b275e47e09e859823e965a1eb323dc (diff) | |
| download | glibc-524ae9ea2e3ae9f5bf5d655595fda827e9dc50a1.tar.gz | |
Fix ldbl-128ibm ilogbl near powers of 2 (bug 18029).
The ldbl-128ibm implementation of ilogbl 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, ilogbl
(0x1.ffffffffffffffp1L) returns 2 but should return 1. (This is
similar to (fixed) bug 16740 for frexpl, and bug 18030 for logbl.)
This patch adds checks for that case.
Tested for powerpc.
[BZ #18029]
* sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c (__ieee754_ilogbl):
Adjust exponent of power of 2 down when low part has opposite
sign.
* math/libm-test.inc (ilogb_test_data): Add more tests.
Diffstat (limited to 'sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c')
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c b/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c index aeace7c977..4088238f30 100644 --- a/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c +++ b/sysdeps/ieee754/ldbl-128ibm/e_ilogbl.c @@ -31,12 +31,13 @@ static char rcsid[] = "$NetBSD: $"; int __ieee754_ilogbl(long double x) { - int64_t hx; + int64_t hx, hxs; int ix; - double xhi; + double xhi, xlo; - xhi = ldbl_high (x); + ldbl_unpack (x, &xhi, &xlo); EXTRACT_WORDS64 (hx, xhi); + hxs = hx; hx &= 0x7fffffffffffffffLL; if(hx <= 0x0010000000000000LL) { if(hx==0) @@ -45,7 +46,21 @@ int __ieee754_ilogbl(long double x) for (ix = -1022, hx<<=11; hx>0; hx<<=1) ix -=1; return ix; } - else if (hx<0x7ff0000000000000LL) return (hx>>52)-0x3ff; + else if (hx < 0x7ff0000000000000LL) + { + int hexp = (hx >> 52) - 0x3ff; + /* 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. */ + if ((hx & 0x000fffffffffffffLL) == 0) + { + int64_t lx; + EXTRACT_WORDS64 (lx, xlo); + if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0) + hexp--; + } + return hexp; + } else if (FP_ILOGBNAN != INT_MAX) { /* ISO C99 requires ilogbl(+-Inf) == INT_MAX. */ if (hx==0x7ff0000000000000LL) |