From 3b6da19781db32ad406eca6b8c37f7d6057f21e8 Mon Sep 17 00:00:00 2001
From: blueloveTH <blueloveTH@foxmail.com>
Date: Fri, 16 Jun 2023 00:51:42 +0800
Subject: [PATCH] ...

---
 src/pocketpy.h | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/pocketpy.h b/src/pocketpy.h
index a307f25e..2fc59c04 100644
--- a/src/pocketpy.h
+++ b/src/pocketpy.h
@@ -100,15 +100,26 @@ inline void init_builtins(VM* _vm) {
         return VAR(MappingProxy(mod));
     });
 
+    static const auto _mul = [](i64 a, i64 b, i64 c){
+        if(c < 16384) return (a%c) * (b%c) % c;
+        i64 res = 0;
+        while(b > 0){
+            if(b & 1) res = (res + a) % c;
+            a = (a << 1) % c;
+            b >>= 1;
+        }
+        return res;
+    };
+
     _vm->bind_builtin_func<3>("pow", [](VM* vm, ArgsView args) {
         i64 lhs = CAST(i64, args[0]);   // assume lhs>=0
         i64 rhs = CAST(i64, args[1]);   // assume rhs>=0
         i64 mod = CAST(i64, args[2]);   // assume mod>0, mod*mod should not overflow
         i64 res = 1;
+        lhs %= mod;
         while(rhs){
-            i64 lhs_mod = lhs % mod;
-            if(rhs & 1) res = ((res % mod) * lhs_mod) % mod;
-            lhs = (lhs_mod * lhs_mod) % mod;
+            if(rhs & 1) res = _mul(res, lhs, mod);
+            lhs = _mul(lhs, lhs, mod);
             rhs >>= 1;
         }
         return VAR(res);