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| author | Aurelien Jarno <aurelien@aurel32.net> | 2022-10-10 00:39:33 +0200 |
|---|---|---|
| committer | Aurelien Jarno <aurelien@aurel32.net> | 2022-10-24 20:48:02 +0200 |
| commit | 2b5478569e72ee4820a6e163d306690c9c0eaf5e (patch) | |
| tree | 0459a7d695437015b85ab2a3f8bcce24eab1d39f | |
| parent | be930668eccf842d5a1a068a3e01b660d5bcb813 (diff) | |
| download | glibc-2b5478569e72ee4820a6e163d306690c9c0eaf5e.tar.gz glibc-2b5478569e72ee4820a6e163d306690c9c0eaf5e.tar.xz glibc-2b5478569e72ee4820a6e163d306690c9c0eaf5e.zip | |
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>
| -rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/s_llroundl.c | 21 |
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 |