⚡️ 优化 abs

utils/math/math.go

@@ -17,18 +17,31 @@ func Min(a, b int) int {
 	return a
 }
 
+// intSize is either 32 or 64.
+const intSize = 32 << (^uint(0) >> 63)
+
 // Abs 返回绝对值，该函数将被内联
 func Abs(x int) int {
-	if x < 0 {
+	// m := -1 if x < 0. m := 0 otherwise.
-		return -x
+	m := x >> (intSize - 1)
-	}
+
-	return x
+	// In two's complement representation, the negative number
+	// of any number (except the smallest one) can be computed
+	// by flipping all the bits and add 1. This is faster than
+	// code with a branch.
+	// See Hacker's Delight, section 2-4.
+	return (x ^ m) - m
 }
 
 // Abs64 返回绝对值，该函数将被内联
 func Abs64(x int64) int64 {
-	if x < 0 {
+	// m := -1 if x < 0. m := 0 otherwise.
-		return -x
+	m := x >> (64 - 1)
-	}
+
-	return x
+	// In two's complement representation, the negative number
+	// of any number (except the smallest one) can be computed
+	// by flipping all the bits and add 1. This is faster than
+	// code with a branch.
+	// See Hacker's Delight, section 2-4.
+	return (x ^ m) - m
 }