exmath.Round 精度为负数时结算精准度问题 (#15)

Author: thinkeridea

exmath/benchmark/round_test.go

@@ -7,8 +7,19 @@ import (
 )
 
 func BenchmarkRound(b *testing.B) {
-	f := 0.15807659924030304
 	for i := 0; i < b.N; i++ {
-		_ = exmath.Round(f, 5)
+		_ = exmath.Round(169543.34596, 0)
+	}
+}
+
+func BenchmarkRoundDecimal(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = exmath.Round(0.15807659924030304, 5)
+	}
+}
+
+func BenchmarkRoundInteger(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = exmath.Round(169543.34596, -5)
 	}
 }

exmath/round.go

@@ -10,6 +10,14 @@ import (
 // Round 四舍五入，ROUND_HALF_UP 模式实现
 // 返回将 val 根据指定精度 precision（十进制小数点后数字的数目）进行四舍五入的结果。precision 也可以是负数或零。
 func Round(val float64, precision int) float64 {
+	if precision == 0 {
+		return math.Round(val)
+	}
+
 	p := math.Pow10(precision)
+	if precision < 0 {
+		return math.Floor(val*p+0.5) * math.Pow10(-precision)
+	}
+
 	return math.Floor(val*p+0.5) / p
 }

exmath/round_test.go

@@ -4,6 +4,7 @@
 package exmath
 
 import (
+	"fmt"
 	"math"
 	"testing"
 )
@@ -27,11 +28,11 @@ func TestRound(t *testing.T) {
 
 		{0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
 		{1.390671161567e-309, 0, 0, 0, 0, 0, 0, 0, 0, 0},               // denormal
-		{0.49999999999999994, 0, 1, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5}, // 0.5-epsilon
+		{0.49999999999999994, 0, 0, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5}, // 0.5-epsilon
 		{0.5, 0, 1, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5},
 		{0.5000000000000001, 0, 1, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5, 0.5}, // 0.5+epsilon
-		{-1.5, 0, -1, -1.5, -1.5, -1.5, -1.5, -1.5, -1.5, -1.5},
-		{-2.5, 0, -2, -2.5, -2.5, -2.5, -2.5, -2.5, -2.5, -2.5},
+		{-1.5, 0, -2, -1.5, -1.5, -1.5, -1.5, -1.5, -1.5, -1.5},
+		{-2.5, 0, -3, -2.5, -2.5, -2.5, -2.5, -2.5, -2.5, -2.5},
 		{math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN(), math.NaN()},
 		{math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1), math.Inf(1)},
 	}
@@ -44,14 +45,16 @@ func TestRound(t *testing.T) {
 		{2251799813685249.5, 2251799813685249.5, 2251799813685250, 2251799813685250, 2251799813685200, 2251799813685000, 2251799813690000, 2251799813700000, 2251799814000000, 2251799810000000},
 		{2251799813685250.5, 2251799813685250.5, 2251799813685251, 2251799813685250, 2251799813685300, 2251799813685000, 2251799813690000, 2251799813700000, 2251799814000000, 2251799810000000},
 		{4503599627370495.5, 4503599627370495, 4503599627370496, 4503599627370500, 4503599627370500, 4503599627370000, 4503599627370000, 4503599627400000, 4503599627000000, 4503599630000000},
-		{4503599627370497, 4503599627370497, 4503599627370498, 4503599627370500, 4503599627370500, 4503599627370000, 4503599627370000, 4503599627400000, 4503599627000000, 4503599630000000},
+		{4503599627370497, 4503599627370497, 4503599627370497, 4503599627370500, 4503599627370500, 4503599627370000, 4503599627370000, 4503599627400000, 4503599627000000, 4503599630000000},
+		{169543.34596, 169543.3, 169543, 169540, 169500, 170000, 170000, 200000, 0, 0},
 	}
 
 	for _, cases := range vf {
 		expected := []float64{cases.pm1, cases.p0, cases.p1, cases.p2, cases.p3, cases.p4, cases.p5, cases.p6, cases.p7}
 		for precision := -1; precision < 8; precision++ {
 			if actual := Round(cases.v, precision); actual != expected[precision+1] && !(math.IsNaN(actual) && math.IsNaN(expected[precision+1])) {
-				t.Errorf("Round(%f, %d) %f != %f", cases.v, precision, actual, expected[precision+1])
+				fmt.Println(cases.v, precision, actual, Round(0.5, precision))
+				t.Errorf("Round(%v, %d) %f != %f", cases.v, precision, actual, expected[precision+1])
 			}
 		}
 	}