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powerpc: Fix logbl on power7 [BZ# 21280]

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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

	[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.
This commit is contained in:
Tulio Magno Quites Machado Filho 2017-04-28 19:45:52 -03:00
parent 2f7f3cd8cd
commit c064f6a613
2 changed files with 25 additions and 6 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2017-04-28 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.
2017-04-28 Paul E. Murphy <murphyp@linux.vnet.ibm.com>
* sysdeps/powerpc/powerpc64le/Implies: New file.

24
sysdeps/powerpc/power7/fpu/s_logbl.c
View File

@ -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;