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Fix ldbl-128ibm lrintl, lroundl missing "invalid" exceptions (bug 22690).

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The ldbl-128ibm implementations of lrintl and lroundl are missing
"invalid" exceptions for certain overflow cases when compiled with GCC
8.  The cause of this is after-the-fact integer overflow checks that
fail when the compiler optimizes on the basis of integer overflow
being undefined; GCC 8 must be able to detect new cases of
undefinedness here.

Failure: lrint (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_downward (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_towardzero (-0x80000001p0): Exception "Invalid operation" not set
Failure: lrint_upward (-0x80000001p0): Exception "Invalid operation" not set

Failure: lround (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_downward (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_towardzero (-0x80000001p0): Exception "Invalid operation" not set
Failure: lround_upward (-0x80000001p0): Exception "Invalid operation" not set

(Tested that these failures occur before the patch for powerpc
soft-float, but the issue applies in principle for hard-float as well,
whether or not the particular optimizations in fact occur there at
present.)

This patch fixes the bug by ensuring the additions / subtractions in
question cast arguments to unsigned long int, or use 1UL as a constant
argument, so that the arithmetic occurs in an unsigned type with the
result then converted back to a signed type.

Tested for powerpc (soft-float).

	[BZ #22690]
	* sysdeps/ieee754/ldbl-128ibm/s_lrintl.c (__lrintl): Use unsigned
	long int for arguments of possibly overflowing addition or
	subtraction.
	* sysdeps/ieee754/ldbl-128ibm/s_lroundl.c (__lroundl): Likewise.
This commit is contained in:
Joseph Myers 2018-01-10 00:02:35 +00:00
parent b2584ac2a4
commit 1272748886
3 changed files with 20 additions and 12 deletions
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8
ChangeLog
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@ -1,3 +1,11 @@
2018-01-10 Joseph Myers <joseph@codesourcery.com>
[BZ #22690]
* sysdeps/ieee754/ldbl-128ibm/s_lrintl.c (__lrintl): Use unsigned
long int for arguments of possibly overflowing addition or
subtraction.
* sysdeps/ieee754/ldbl-128ibm/s_lroundl.c (__lroundl): Likewise.
2018-01-09 Joseph Myers <joseph@codesourcery.com>
[BZ #22688]

14
sysdeps/ieee754/ldbl-128ibm/s_lrintl.c
View File

@ -84,7 +84,7 @@ __lrintl (long double x)
/* Peg at max/min values, assuming that the above conversions do so.
Strictly speaking, we can return anything for values that overflow,
but this is more useful. */
res = hi + lo;
res = (long int) ((unsigned long int) hi + (unsigned long int) lo);
/* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */
if (__glibc_unlikely (((~(hi ^ lo) & (res ^ hi)) < 0)))
@ -105,27 +105,27 @@ __lrintl (long double x)
return res;
if (xh < 0.0)
res -= 1;
res -= 1UL;
else
res += 1;
res += 1UL;
break;
case FE_TOWARDZERO:
if (res > 0 && (xh < 0.0 || (xh == 0.0 && xl < 0.0)))
res -= 1;
res -= 1UL;
else if (res < 0 && (xh > 0.0 || (xh == 0.0 && xl > 0.0)))
res += 1;
res += 1UL;
return res;
break;
case FE_UPWARD:
if (xh > 0.0 || (xh == 0.0 && xl > 0.0))
res += 1;
res += 1UL;
break;
case FE_DOWNWARD:
if (xh < 0.0 || (xh == 0.0 && xl < 0.0))
res -= 1;
res -= 1UL;
break;
}

10
sysdeps/ieee754/ldbl-128ibm/s_lroundl.c
View File

@ -80,7 +80,7 @@ __lroundl (long double x)
/* Peg at max/min values, assuming that the above conversions do so.
Strictly speaking, we can return anything for values that overflow,
but this is more useful. */
res = hi + lo;
res = (long int) ((unsigned long int) hi + (unsigned long int) lo);
/* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */
if (__glibc_unlikely (((~(hi ^ lo) & (res ^ hi)) < 0)))
@ -92,21 +92,21 @@ __lroundl (long double x)
hi = res;
if (xh > 0.5)
{
res += 1;
res += 1UL;
}
else if (xh == 0.5)
{
if (xl > 0.0 || (xl == 0.0 && res >= 0))
res += 1;
res += 1UL;
}
else if (-xh > 0.5)
{
res -= 1;
res -= 1UL;
}
else if (-xh == 0.5)
{
if (xl < 0.0 || (xl == 0.0 && res <= 0))
res -= 1;
res -= 1UL;
}
if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0)))