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UB in negate in mulh/mulhsu #1546

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Jan 18, 2025
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UB in negate in mulh/mulhsu #1546

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6 changes: 3 additions & 3 deletions riscv/arith.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,15 +32,15 @@ inline uint64_t mulhu(uint64_t a, uint64_t b)
inline int64_t mulh(int64_t a, int64_t b)
{
int negate = (a < 0) != (b < 0);
uint64_t res = mulhu(a < 0 ? -a : a, b < 0 ? -b : b);
uint64_t res = mulhu(a < 0 ? -(uint64_t)a : a, b < 0 ? -(uint64_t)b : b);
return negate ? ~res + ((uint64_t)a * (uint64_t)b == 0) : res;
}

inline int64_t mulhsu(int64_t a, uint64_t b)
{
int negate = a < 0;
uint64_t res = mulhu(a < 0 ? -a : a, b);
return negate ? ~res + (a * b == 0) : res;
uint64_t res = mulhu(a < 0 ? -(uint64_t)a : a, b);
return negate ? ~res + ((uint64_t)a * b == 0) : res;
}

//ref: https://locklessinc.com/articles/sat_arithmetic/
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