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math: Fix UB in ldbl-128ibm llroundl

This commit is contained in:
Adhemerval Zanella 2025-05-08 12:21:06 +00:00
parent 623bd741fb
commit d044eb659e
1 changed files with 16 additions and 7 deletions
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23
sysdeps/ieee754/ldbl-128ibm/s_lroundl.c
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@ -23,12 +23,20 @@
#include <math_ldbl_opt.h> #include <math_ldbl_opt.h>
#include <float.h> #include <float.h>
#include <ieee754.h> #include <ieee754.h>
#include <intprops.h>
static inline bool
check_sign (unsigned long int v1, unsigned long int v2)
{
enum { sign_shift = sizeof (unsigned long int) * CHAR_BIT - 1 };
return (v1 & (1UL << sign_shift)) == (v2 & (1UL << sign_shift));
}
long long
__lroundl (long double x) __lroundl (long double x)
{ {
double xh, xl; double xh, xl;
long res, hi, lo; long res, hi, lo, tmp;
ldbl_unpack (x, &xh, &xl); ldbl_unpack (x, &xh, &xl);
@ -84,7 +92,7 @@ __lroundl (long double x)
res = (long int) ((unsigned long int) hi + (unsigned long int) lo); res = (long int) ((unsigned long int) hi + (unsigned long int) lo);
/* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */ /* This is just sign(hi) == sign(lo) && sign(res) != sign(hi). */
if (__glibc_unlikely (((~(hi ^ lo) & (res ^ hi)) < 0))) if (__glibc_unlikely (check_sign (hi, lo) && !check_sign (res, hi)))
goto overflow; goto overflow;
xh -= lo; xh -= lo;
@ -93,24 +101,25 @@ __lroundl (long double x)
hi = res; hi = res;
if (xh > 0.5) if (xh > 0.5)
{ {
res += 1UL; INT_ADD_WRAPV (res, 1, &res);
} }
else if (xh == 0.5) else if (xh == 0.5)
{ {
if (xl > 0.0 || (xl == 0.0 && res >= 0)) if (xl > 0.0 || (xl == 0.0 && res >= 0))
res += 1UL; INT_ADD_WRAPV (res, 1, &res);
} }
else if (-xh > 0.5) else if (-xh > 0.5)
{ {
res -= 1UL; INT_SUBTRACT_WRAPV (res, 1UL, &res);
} }
else if (-xh == 0.5) else if (-xh == 0.5)
{ {
if (xl < 0.0 || (xl == 0.0 && res <= 0)) if (xl < 0.0 || (xl == 0.0 && res <= 0))
res -= 1UL; INT_SUBTRACT_WRAPV (res, 1UL, &res);
} }
if (__glibc_unlikely (((~(hi ^ (res - hi)) & (res ^ hi)) < 0))) INT_SUBTRACT_WRAPV (res, hi, &tmp);
if (__glibc_unlikely (check_sign (hi, tmp) && !check_sign (res, hi)))
goto overflow; goto overflow;
return res; return res;