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Avoid overflowing shift by special casing inverse of 1 #81

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Merged
merged 1 commit into from
Apr 12, 2024
Merged

Avoid overflowing shift by special casing inverse of 1 #81

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3 changes: 2 additions & 1 deletion src/int_utils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -194,6 +194,7 @@ class BitsInt {
}

static constexpr inline bool IsZero(I a) { return a == 0; }
static constexpr inline bool IsOne(I a) { return a == 1; }
static constexpr inline I Mask(I val) { return val & MASK; }
static constexpr inline I Shift(I val, int bits) { return ((val << bits) & MASK); }
static constexpr inline I UnsafeShift(I val, int bits) { return (val << bits); }
Expand Down Expand Up @@ -252,7 +253,7 @@ template<typename I, int N, typename L, typename F> inline constexpr I GFMul(con
template<typename I, typename F, int BITS, uint32_t MOD>
inline I InvExtGCD(I x)
{
if (F::IsZero(x)) return x;
if (F::IsZero(x) || F::IsOne(x)) return x;
I t(0), newt(1);
I r(MOD), newr = x;
int rlen = BITS + 1, newrlen = F::Bits(newr, BITS);
Expand Down