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Avoid negation of signed integers in C that may hold INT*_MIN.

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Reported by minoki.
Recent C compilers 'take advantage' of the undefined behavior.
This completely changes the meaning of expressions like (k == -k).
This commit is contained in:
Mike Pall
2022-12-22 00:03:06 +01:00
parent b2791179ef
commit 8a5e398c52
12 changed files with 32 additions and 32 deletions
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8
src/lj_vmmath.c
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@@ -66,11 +66,11 @@ int32_t LJ_FASTCALL lj_vm_modi(int32_t a, int32_t b)
{
uint32_t y, ua, ub;
lua_assert(b != 0); /* This must be checked before using this function. */
ua = a < 0 ? (uint32_t)-a : (uint32_t)a;
ub = b < 0 ? (uint32_t)-b : (uint32_t)b;
ua = a < 0 ? ~(uint32_t)a+1u : (uint32_t)a;
ub = b < 0 ? ~(uint32_t)b+1u : (uint32_t)b;
y = ua % ub;
if (y != 0 && (a^b) < 0) y = y - ub;
if (((int32_t)y^b) < 0) y = (uint32_t)-(int32_t)y;
if (((int32_t)y^b) < 0) y = ~y+1u;
return (int32_t)y;
}
#endif
@@ -105,7 +105,7 @@ double lj_vm_powi(double x, int32_t k)
else if (k == 0)
return 1.0;
else
return 1.0 / lj_vm_powui(x, (uint32_t)-k);
return 1.0 / lj_vm_powui(x, ~(uint32_t)k+1u);
}
/* Computes fpm(x) for extended math functions. */