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mruby-bigint: inline in-place subtraction into mpz_sub

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move in-place optimization directly into mpz_sub() so callers
just use mpz_sub(ctx, x, x, y) and get automatic optimization.
remove separate mpz_sub_inplace() function.

Co-authored-by: Claude <noreply@anthropic.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2026-01-15 08:34:32 +09:00
parent c048ccc88a
commit 3b41d66299
1 changed files with 12 additions and 18 deletions
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mrbgems/mruby-bigint/core/bigint.c
+12 -18
View File
@@ -598,29 +598,23 @@ mpz_add_int(mpz_ctx_t *ctx, mpz_t *x, mrb_int n)
trim(x);
}
/* z = x - y -- just use mpz_add - I'm lazy */
/* z = x - y */
static void
mpz_sub(mpz_ctx_t *ctx, mpz_t *z, mpz_t *x, mpz_t *y)
{
mpz_t u;
/* In-place optimization: z == x, both positive, x >= y */
if (z == x && x->sn > 0 && y->sn > 0 && ucmp(x, y) >= 0) {
usub_inplace(x, y);
if (x->sz == 0) x->sn = 0;
return;
}
/* Initialize u as a view of y with negated sign - no new memory allocated */
/* General case: create view of y with negated sign and use mpz_add */
mpz_t u;
u.p = y->p;
u.sz = y->sz;
u.sn = -(y->sn);
mpz_add(ctx, z, x, &u);
/* No mpz_clear needed since u.p points to y->p (no separate allocation) */
}
/* In-place signed subtraction: x -= y */
/* Precondition: x > 0, y > 0, x >= y (caller must ensure this) */
/* No allocation when preconditions are met */
static void
mpz_sub_inplace(mpz_t *x, mpz_t *y)
{
/* Caller guarantees: x->sn > 0, y->sn > 0, ucmp(x, y) >= 0 */
usub_inplace(x, y);
if (x->sz == 0) x->sn = 0;
}
/* x -= n */
@@ -1688,7 +1682,7 @@ mpz_mul_all_ones_body(mrb_state *mrb, void *userdata)
/* Subtract 2^(n+1) */
mpz_set_int(ctx, &d->a, 1);
mpz_mul_2exp(ctx, &d->a, &d->a, n+1);
mpz_sub_inplace(w, &d->a); /* w >= d->a guaranteed */
mpz_sub(ctx, w, w, &d->a);
/* Add 1 */
mpz_add_int(ctx, w, 1);
@@ -1705,12 +1699,12 @@ mpz_mul_all_ones_body(mrb_state *mrb, void *userdata)
/* Subtract 2^n */
mpz_set_int(ctx, &d->a, 1);
mpz_mul_2exp(ctx, &d->a, &d->a, n);
mpz_sub_inplace(w, &d->a); /* w >= d->a guaranteed */
mpz_sub(ctx, w, w, &d->a);
/* Subtract 2^m */
mpz_set_int(ctx, &d->b, 1);
mpz_mul_2exp(ctx, &d->b, &d->b, m);
mpz_sub_inplace(w, &d->b); /* w >= d->b guaranteed */
mpz_sub(ctx, w, w, &d->b);
/* Add 1 */
mpz_add_int(ctx, w, 1);