diff --git a/i2a.c b/i2a.c
index 3796367..dabc23b 100644
--- a/i2a.c
+++ b/i2a.c
@@ -75,7 +75,7 @@ static _INLINE unsigned char _utoa(char* c, unsigned int i, unsigned char o) {
 	  c[o++] = _c3DigitsLut[a + 1];
 	  c[o++] = _c3DigitsLut[a + 2];
 	} else {
-	  a *= 2;
+		a <<= 1;
 	  c[o++] = _c2DigitsLut[a];
 	  c[o++] = _c2DigitsLut[a + 1];
 	}
diff --git a/itoa.h b/itoa.h
index 43a4016..81e5ba7 100644
--- a/itoa.h
+++ b/itoa.h
@@ -54,8 +54,7 @@ extern "C" {
 #endif
   //not use, just for u64toa
   _INLINE static unsigned char _utoa(char* c, unsigned int i, unsigned char o) {
-	//4294967295
-	if (i < 1000000) {
+	if (i < _cRadix4D) {
 	  const unsigned int a = (i / _cRadix2D) << 1;
 	  const unsigned int b = (i % _cRadix2D) << 1;
 	  if (i > 999) c[o++] = _c2DigitsLut[a];
@@ -87,7 +86,7 @@ extern "C" {
 		c[o++] = _c3DigitsLut[a + 1];
 		c[o++] = _c3DigitsLut[a + 2];
 	  } else {
-		a *= 2;
+		a <<= 1;
 		c[o++] = _c2DigitsLut[a];
 		c[o++] = _c2DigitsLut[a + 1];
 	  }