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authorAurelien Jarno <aurelien@aurel32.net>2022-10-10 00:39:33 +0200
committerAurelien Jarno <aurelien@aurel32.net>2022-10-24 20:48:02 +0200
commit2b5478569e72ee4820a6e163d306690c9c0eaf5e (patch)
tree0459a7d695437015b85ab2a3f8bcce24eab1d39f /sysdeps/ieee754
parentbe930668eccf842d5a1a068a3e01b660d5bcb813 (diff)
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Avoid undefined behaviour in ibm128 implementation of llroundl (BZ #29488)
Detecting an overflow edge case depended on signed overflow of a long long. Replace the additions and the overflow checks by __builtin_add_overflow(). Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>
Diffstat (limited to 'sysdeps/ieee754')
-rw-r--r--sysdeps/ieee754/ldbl-128ibm/s_llroundl.c21
1 files changed, 9 insertions, 12 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
index d85154e73a..d8c0de1faf 100644
--- a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
+++ b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
@@ -66,38 +66,35 @@ __llroundl (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;
-
- /* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */
- if (__glibc_unlikely (((~(hi ^ lo) & (res ^ hi)) < 0)))
+ if (__glibc_unlikely (__builtin_add_overflow (hi, lo, &res)))
goto overflow;
xh -= lo;
ldbl_canonicalize (&xh, &xl);
- hi = res;
if (xh > 0.5)
{
- res += 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, 1, &res)))
+ goto overflow;
}
else if (xh == 0.5)
{
if (xl > 0.0 || (xl == 0.0 && res >= 0))
- res += 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, 1, &res)))
+ goto overflow;
}
else if (-xh > 0.5)
{
- res -= 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, -1, &res)))
+ goto overflow;
}
else if (-xh == 0.5)
{
if (xl < 0.0 || (xl == 0.0 && res <= 0))
- res -= 1;
+ if (__glibc_unlikely (__builtin_add_overflow (res, -1, &res)))
+ goto overflow;
}
- if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0)))
- goto overflow;
-
return res;
}
else