Avoid undefined behaviour in ibm128 implementation of llroundl
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| dj/TryBot-apply_patch |
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Patch applied to master at the time it was sent
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| dj/TryBot-32bit |
success
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Build for i686
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Commit Message
Detecting an overflow edge case depended on signed overflow of a long
long. Replace the signed long long with unsigned and cast it back to
unsigned before comparisons (which is implementation defined behaviour,
but I guess glibc does not support any one's complement
architectures...).
BZ #29488
---
sysdeps/ieee754/ldbl-128ibm/s_llroundl.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
Comments
Disregard this, I hadn't run all the tests I thought I had, sorry about
that.
On Sun, 21 Aug 2022 at 22:45, Michael Hudson-Doyle <
michael.hudson@canonical.com> wrote:
> Detecting an overflow edge case depended on signed overflow of a long
> long. Replace the signed long long with unsigned and cast it back to
> unsigned before comparisons (which is implementation defined behaviour,
> but I guess glibc does not support any one's complement
> architectures...).
>
> BZ #29488
> ---
> sysdeps/ieee754/ldbl-128ibm/s_llroundl.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
> b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
> index d85154e73a..e8117bfc2b 100644
> --- a/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
> +++ b/sysdeps/ieee754/ldbl-128ibm/s_llroundl.c
> @@ -28,7 +28,8 @@ long long
> __llroundl (long double x)
> {
> double xh, xl;
> - long long res, hi, lo;
> + unsigned long long res;
> + long long hi, lo;
>
> ldbl_unpack (x, &xh, &xl);
>
> @@ -69,7 +70,7 @@ __llroundl (long double x)
> 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 (((~(hi ^ lo) & (((long long)res) ^ hi)) < 0)))
> goto overflow;
>
> xh -= lo;
> @@ -95,7 +96,7 @@ __llroundl (long double x)
> res -= 1;
> }
>
> - if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0)))
> + if (__glibc_unlikely (((~(hi ^ (((long long)res) - hi)) & (((long
> long)res) ^ hi)) < 0)))
> goto overflow;
>
> return res;
> --
> 2.34.1
>
>
@@ -28,7 +28,8 @@ long long
__llroundl (long double x)
{
double xh, xl;
- long long res, hi, lo;
+ unsigned long long res;
+ long long hi, lo;
ldbl_unpack (x, &xh, &xl);
@@ -69,7 +70,7 @@ __llroundl (long double x)
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 (((~(hi ^ lo) & (((long long)res) ^ hi)) < 0)))
goto overflow;
xh -= lo;
@@ -95,7 +96,7 @@ __llroundl (long double x)
res -= 1;
}
- if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0)))
+ if (__glibc_unlikely (((~(hi ^ (((long long)res) - hi)) & (((long long)res) ^ hi)) < 0)))
goto overflow;
return res;