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Merge pull request #4416 from Yawning/fix/4413

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src/big_int.cpp: Use square-multiply for exponentiation
This commit is contained in:
gingerBill
2024-10-27 12:13:40 +00:00
committed by GitHub
parent 35d818bb4e 61795232f4
commit 1f187adff4
1 changed files with 14 additions and 3 deletions
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17
src/big_int.cpp
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@@ -62,6 +62,7 @@ gb_internal void big_int_shl (BigInt *dst, BigInt const *x, BigInt const *y);
gb_internal void big_int_shr (BigInt *dst, BigInt const *x, BigInt const *y);
gb_internal void big_int_mul (BigInt *dst, BigInt const *x, BigInt const *y);
gb_internal void big_int_mul_u64(BigInt *dst, BigInt const *x, u64 y);
gb_internal void big_int_exp_u64(BigInt *dst, BigInt const *x, u64 y, bool *success);
gb_internal void big_int_quo_rem(BigInt const *x, BigInt const *y, BigInt *q, BigInt *r);
gb_internal void big_int_quo (BigInt *z, BigInt const *x, BigInt const *y);
@@ -250,9 +251,7 @@ gb_internal void big_int_from_string(BigInt *dst, String const &s, bool *success
exp *= 10;
exp += v;
}
for (u64 x = 0; x < exp; x++) {
big_int_mul_eq(dst, &b);
}
big_int_exp_u64(dst, &b, exp, success);
}
if (is_negative) {
@@ -328,6 +327,18 @@ gb_internal void big_int_mul_u64(BigInt *dst, BigInt const *x, u64 y) {
big_int_dealloc(&d);
}
gb_internal void big_int_exp_u64(BigInt *dst, BigInt const *x, u64 y, bool *success) {
if (y > INT_MAX) {
*success = false;
return;
}
// Note: The cutoff for square-multiply being faster than the naive
// for loop is when exp > 4, but it probably isn't worth adding
// a fast path.
mp_err err = mp_expt_n(x, int(y), dst);
*success = err == MP_OKAY;
}
gb_internal void big_int_mul(BigInt *dst, BigInt const *x, BigInt const *y) {
mp_mul(x, y, dst);