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mruby-bigint: Apply 4x loop unrolling to uadd for performance

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Improved the `uadd` function by applying 4x loop unrolling to its core addition
loops. This optimization aims to reduce loop overhead and improve
instruction-level parallelism, leading to better performance for multi-limb
addition operations.

Co-authored-by: Gemini <gemini@google.com>
This commit is contained in:
Yukihiro "Matz" Matsumoto
2025-07-31 09:50:53 +09:00
parent 3bad1874a8
commit 1d7ef2b85b
1 changed files with 41 additions and 1 deletions
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mrbgems/mruby-bigint/core/bigint.c
+41 -1
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@@ -347,13 +347,53 @@ uadd(mpz_t *z, mpz_t *x, mpz_t *y)
size_t i;
/* Add overlapping limbs from both operands */
for (i = 0; i < x->sz; i++) {
/* 4x unrolled loop for better performance */
for (i = 0; i + 4 <= x->sz; i += 4) {
c += (mp_dbl_limb)y->p[i] + (mp_dbl_limb)x->p[i];
z->p[i] = LOW(c);
c >>= DIG_SIZE;
c += (mp_dbl_limb)y->p[i+1] + (mp_dbl_limb)x->p[i+1];
z->p[i+1] = LOW(c);
c >>= DIG_SIZE;
c += (mp_dbl_limb)y->p[i+2] + (mp_dbl_limb)x->p[i+2];
z->p[i+2] = LOW(c);
c >>= DIG_SIZE;
c += (mp_dbl_limb)y->p[i+3] + (mp_dbl_limb)x->p[i+3];
z->p[i+3] = LOW(c);
c >>= DIG_SIZE;
}
/* Handle remaining elements */
for (; i < x->sz; i++) {
c += (mp_dbl_limb)y->p[i] + (mp_dbl_limb)x->p[i];
z->p[i] = LOW(c);
c >>= DIG_SIZE;
}
/* Add remaining limbs from larger operand */
/* 4x unrolled loop for better performance */
for (; i + 4 <= y->sz; i += 4) {
c += y->p[i];
z->p[i] = LOW(c);
c >>= DIG_SIZE;
c += y->p[i+1];
z->p[i+1] = LOW(c);
c >>= DIG_SIZE;
c += y->p[i+2];
z->p[i+2] = LOW(c);
c >>= DIG_SIZE;
c += y->p[i+3];
z->p[i+3] = LOW(c);
c >>= DIG_SIZE;
}
/* Handle remaining elements */
for (; i < y->sz; i++) {
c += y->p[i];
z->p[i] = LOW(c);