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[PATCH] powerpc: Fix logbl on power7 [BZ# 21280]
- From: "Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Mon, 20 Mar 2017 18:02:58 -0300
- Subject: [PATCH] powerpc: Fix logbl on power7 [BZ# 21280]
- Authentication-results: sourceware.org; auth=none
1. Fix the results for negative subnormals by ignoring the signal when
normalizing the value.
2. Fix the output when the high part is a power of 2 and the low part
is a nonzero number with opposite sign. This fix is based on commit
380bd0fd2418f8988217de950f8b8ff18af0cb2b.
After applying this patch, logbl() tests pass cleanly on POWER >= 7.
Tested on powerpc, powerpc64 and powerpc64le
2017-03-20 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
[BZ #21280]
* sysdeps/powerpc/power7/fpu/s_logbl.c (__logbl): Ignore the
signal of subnormals and adjust the exponent of power of 2 down
when low part has opposite sign.
---
sysdeps/powerpc/power7/fpu/s_logbl.c | 24 ++++++++++++++++++------
1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/sysdeps/powerpc/power7/fpu/s_logbl.c b/sysdeps/powerpc/power7/fpu/s_logbl.c
index f7ecbd1..3ae383a 100644
--- a/sysdeps/powerpc/power7/fpu/s_logbl.c
+++ b/sysdeps/powerpc/power7/fpu/s_logbl.c
@@ -35,14 +35,16 @@ static const union {
long double
__logbl (long double x)
{
- double xh;
+ double xh, xl;
double ret;
+ int64_t hx;
if (__builtin_expect (x == 0.0L, 0))
/* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */
return -1.0L / __builtin_fabsl (x);
- xh = ldbl_high (x);
+ ldbl_unpack (x, &xh, &xl);
+ EXTRACT_WORDS64 (hx, xh);
/* ret = x & 0x7ff0000000000000; */
asm (
"xxland %x0,%x1,%x2\n"
@@ -58,10 +60,20 @@ __logbl (long double x)
{
/* POSIX specifies that denormal number is treated as
though it were normalized. */
- int64_t hx;
-
- EXTRACT_WORDS64 (hx, xh);
- return (long double) (-1023 - (__builtin_clzll (hx) - 12));
+ return (long double) (- (__builtin_clzll (hx & 0x7fffffffffffffffLL) \
+ - 12) - 1023);
+ }
+ 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, rhx;
+ EXTRACT_WORDS64 (lx, xl);
+ rhx = (hx & 0x7ff0000000000000LL) >> 52;
+ if ((hx ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
+ rhx--;
+ return (long double) (rhx - 1023);
}
/* Test to avoid logb_downward (0.0) == -0.0. */
return ret == -0.0 ? 0.0 : ret;
--
2.1.0