Fix __builtin_mul

libf.h

@@ -564,26 +564,26 @@ static int __builtin_mul(int a, int b) {
   int i, e, v;
   int d[24];
   int r[24];
-  for (i = 0, e = 1, v = a; e <= b; i++) {
+  for (i = 0, e = 1, v = a;; i++) {
     d[i] = v;
     r[i] = e;
     v += v;
     int ne = e + e;
-    if (ne < e)
+    if (ne < e || ne > b)
       break;
     e = ne;
   }
 
-  int a = 0;
+  int x = 0;
   for (;; i--) {
     if (b >= r[i]) {
-      a += d[i];
+      x += d[i];
       b -= r[i];
     }
     if (i == 0)
       break;
   }
-  return a;
+  return x;
 }
 
 static unsigned int __builtin_div(unsigned int a, unsigned int b) {

test/24_muldiv.c

@@ -1,6 +1,11 @@
 #include "../libf.h"
 
 int main() {
-  printf("%d\n", 10777216 * 10777216);
+  int v = 10777216 * 9777219;
+#ifndef __bfs__
+  v &= ((1 << 24) - 1);
+#endif
+  printf("%d\n", v);
+  printf("%d\n", 10777216 * 0);
   printf("%d\n", 10777216 / 2);
 }