From 5ccca7e45b802051e00e3398ecf036f86ba92843 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 28 Oct 2022 16:59:09 +0900
Subject: [PATCH] mruby-bigint/bigint.c (udiv): skip loop if xd<yd.

---
 mrbgems/mruby-bigint/core/bigint.c | 50 ++++++++++++++++--------------
 1 file changed, 26 insertions(+), 24 deletions(-)

diff --git a/mrbgems/mruby-bigint/core/bigint.c b/mrbgems/mruby-bigint/core/bigint.c
index 5964d0279..1d3edf588 100644
--- a/mrbgems/mruby-bigint/core/bigint.c
+++ b/mrbgems/mruby-bigint/core/bigint.c
@@ -459,34 +459,36 @@ udiv(mrb_state *mrb, mpz_t *qq, mpz_t *rr, mpz_t *xx, mpz_t *yy)
   size_t xd = digits(&x);
   mpz_realloc(mrb, &q, xd);
   mp_dbl_limb z = y.p[yd-1];
-  for (size_t j=xd-yd;; j--) {
-    mp_dbl_limb_signed b=0;
-    mp_dbl_limb qhat;
+  if (xd>=yd) {
+    for (size_t j=xd-yd;; j--) {
+      mp_dbl_limb_signed b=0;
+      mp_dbl_limb qhat;
 
-    if (j+yd == xd)
-      qhat = x.p[j+yd-1] / z;
-    else
-      qhat = (((mp_dbl_limb)x.p[j+yd] << DIG_SIZE) + x.p[j+yd-1]) / z;
-    if (qhat) {
-      for (i=0; i<yd; i++) {
-        mp_dbl_limb zz = qhat * y.p[i];
-        mp_dbl_limb_signed u = LOW(b)+x.p[i+j]-LOW(zz);
-        x.p[i+j] = LOW(u);
-        b = HIGH(b) - HIGH(zz) + HIGH(u);
+      if (j+yd == xd)
+        qhat = x.p[j+yd-1] / z;
+      else
+        qhat = (((mp_dbl_limb)x.p[j+yd] << DIG_SIZE) + x.p[j+yd-1]) / z;
+      if (qhat) {
+        for (i=0; i<yd; i++) {
+          mp_dbl_limb zz = qhat * y.p[i];
+          mp_dbl_limb_signed u = LOW(b)+x.p[i+j]-LOW(zz);
+          x.p[i+j] = LOW(u);
+          b = HIGH(b) - HIGH(zz) + HIGH(u);
+        }
+        b += x.p[i+j];
       }
-      b += x.p[i+j];
-    }
-    for (; b!=0; qhat--) {
-      mp_dbl_limb c = 0;
-      for (i=0; i<yd; i++) {
-        c += (mp_dbl_limb)x.p[i+j] + (mp_dbl_limb)y.p[i];
-        x.p[i+j] = LOW(c);
-        c = HIGH(c);
+      for (; b!=0; qhat--) {
+        mp_dbl_limb c = 0;
+        for (i=0; i<yd; i++) {
+          c += (mp_dbl_limb)x.p[i+j] + (mp_dbl_limb)y.p[i];
+          x.p[i+j] = LOW(c);
+          c = HIGH(c);
+        }
+        b += c;
       }
-      b += c;
+      q.p[j] = (mp_limb)qhat;
+      if (j == 0) break;
     }
-    q.p[j] = (mp_limb)qhat;
-    if (j == 0) break;
   }
   x.sz = yy->sz;
   urshift(mrb, rr, &x, ns);