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bigint.c (mpz_powm): avoid stack allocations.

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This commit is contained in:
Yukihiro "Matz" Matsumoto
2022-08-26 14:21:09 +09:00
parent b158581118
commit f5a3f4f2ea
1 changed files with 10 additions and 49 deletions
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mrbgems/mruby-bigint/core/bigint.c
+10 -49
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@@ -906,44 +906,10 @@ mpz_pow(mrb_state *mrb, mpz_t *zz, mpz_t *x, mrb_int e)
mpz_move(mrb, zz, &t);
}
#define lowdigit(x) (((x)->p)[0])
struct is {
mp_limb v;
struct is *next;
};
static void
push(mrb_state *mrb, mp_limb i, struct is **sp)
{
struct is *tmp;
tmp = *sp;
*sp = (struct is*)mrb_malloc(mrb, sizeof(struct is));
(*sp)->v = i;
(*sp)->next=tmp;
}
static mp_limb
pop(mrb_state *mrb, struct is **sp)
{
struct is *tmp;
mp_limb i;
if (!(*sp))
return (-1);
tmp = *sp;
*sp = (*sp)->next;
i = tmp->v;
tmp->v = 0;
mrb_free(mrb, tmp);
return i;
}
static void
mpz_powm(mrb_state *mrb, mpz_t *zz, mpz_t *x, mrb_int ex, mpz_t *n)
{
mpz_t t, e;
struct is *stack = NULL;
int k, i;
mpz_t t, b;
if (ex == 0) {
mpz_set_int(mrb, zz, 1);
@@ -953,26 +919,21 @@ mpz_powm(mrb_state *mrb, mpz_t *zz, mpz_t *x, mrb_int ex, mpz_t *n)
if (ex < 0) {
return;
}
mpz_init_set_int(mrb, &e, ex);
mpz_init(mrb, &t);
for (k=0; !uzero(&e); k++, mpz_div_2exp(mrb, &e, &e, 1))
push(mrb, lowdigit(&e)&1, &stack);
k--;
i=pop(mrb, &stack);
mpz_init_set_int(mrb, &t, 1);
mpz_init_set(mrb, &b, x);
mpz_mod(mrb, &t, x, n); /* t=x%n */
for (i=k-1;i>=0;i--) {
mpz_mul(mrb, &t, &t, &t);
mpz_mod(mrb, &t, &t, n);
if (pop(mrb, &stack)) {
mpz_mul(mrb, &t, &t, x);
while (ex > 0) {
if ((ex & 1) == 1) {
mpz_mul(mrb, &t, &t, &b);
mpz_mod(mrb, &t, &t, n);
}
ex >>= 1;
mpz_mul(mrb, &b, &b, &b);
mpz_mod(mrb, &b, &b, n);
}
mpz_move(mrb, zz, &t);
mpz_clear(mrb, &e);
mpz_clear(mrb, &b);
}
/* --- mruby functions --- */