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mruby-bigint: add fast path for bitwise ops with positive operands

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skip two's complement conversion in mpz_and, mpz_or, mpz_xor when both
operands are positive. this avoids the per-limb make_2comp overhead and
provides up to 1.6x speedup for large bigints.

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2026-01-14 16:57:14 +09:00
parent 3e695f24d9
commit a7b7885e69
1 changed files with 61 additions and 3 deletions
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mrbgems/mruby-bigint/core/bigint.c
+61 -3
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@@ -3459,10 +3459,24 @@ mpz_and(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y)
}
mrb_assert(x->sz > 0 || y->sz > 0);
/* Fast path: both positive - just AND the limbs */
if (x->sn > 0 && y->sn > 0) {
size_t min_sz = (x->sz < y->sz) ? x->sz : y->sz;
mpz_init_heap(ctx, z, min_sz);
mpz_realloc(ctx, z, min_sz);
for (size_t i = 0; i < min_sz; i++) {
z->p[i] = x->p[i] & y->p[i];
}
z->sn = 1;
trim(z);
return;
}
/* Slow path: at least one negative operand */
size_t max_sz = (x->sz > y->sz) ? x->sz : y->sz;
mpz_init_heap(ctx, z, max_sz);
mpz_realloc(ctx, z, max_sz);
z->sn = (x->sn == y->sn) ? x->sn : 1;
z->sn = (x->sn < 0 && y->sn < 0) ? -1 : 1;
char c1 = 1, c2 = 1, c3 = 1;
for (size_t i = 0; i < max_sz; i++) {
@@ -3479,7 +3493,7 @@ mpz_and(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y)
}
static void
mpz_or(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient way to do this */
mpz_or(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y)
{
if (zero_p(x)) {
mpz_init_heap(ctx, z, y->sz);
@@ -3496,6 +3510,28 @@ mpz_or(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient
mrb_assert(x->sz > 0 || y->sz > 0);
size_t max_sz = (x->sz > y->sz) ? x->sz : y->sz;
/* Fast path: both positive - just OR the limbs */
if (x->sn > 0 && y->sn > 0) {
mpz_init_heap(ctx, z, max_sz);
mpz_realloc(ctx, z, max_sz);
size_t min_sz = (x->sz < y->sz) ? x->sz : y->sz;
for (size_t i = 0; i < min_sz; i++) {
z->p[i] = x->p[i] | y->p[i];
}
/* Copy remaining limbs from the longer operand */
if (x->sz > y->sz) {
for (size_t i = min_sz; i < max_sz; i++) z->p[i] = x->p[i];
}
else {
for (size_t i = min_sz; i < max_sz; i++) z->p[i] = y->p[i];
}
z->sn = 1;
trim(z);
return;
}
/* Slow path: at least one negative operand */
mpz_init_heap(ctx, z, max_sz);
mpz_realloc(ctx, z, max_sz);
z->sn = (x->sn == y->sn) ? x->sn : -1;
@@ -3515,7 +3551,7 @@ mpz_or(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient
}
static void
mpz_xor(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient way to do this */
mpz_xor(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y)
{
if (zero_p(x)) {
mpz_init_heap(ctx, z, y->sz);
@@ -3532,6 +3568,28 @@ mpz_xor(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y) /* not the most efficient
mrb_assert(x->sz > 0 || y->sz > 0);
size_t max_sz = (x->sz > y->sz) ? x->sz : y->sz;
/* Fast path: both positive - just XOR the limbs */
if (x->sn > 0 && y->sn > 0) {
mpz_init_heap(ctx, z, max_sz);
mpz_realloc(ctx, z, max_sz);
size_t min_sz = (x->sz < y->sz) ? x->sz : y->sz;
for (size_t i = 0; i < min_sz; i++) {
z->p[i] = x->p[i] ^ y->p[i];
}
/* Copy remaining limbs from the longer operand (XOR with 0) */
if (x->sz > y->sz) {
for (size_t i = min_sz; i < max_sz; i++) z->p[i] = x->p[i];
}
else {
for (size_t i = min_sz; i < max_sz; i++) z->p[i] = y->p[i];
}
z->sn = 1;
trim(z);
return;
}
/* Slow path: at least one negative operand */
mpz_init_heap(ctx, z, max_sz);
mpz_realloc(ctx, z, max_sz);
z->sn = (x->sn == y->sn) ? 1 : -1;