add Truncate: returns the float32/float64 of the specified precision

math.go

@@ -121,3 +121,19 @@ func Round[T float64 | float32](f T, n ...int) T {
 	pow10N := math.Pow10(nn)
 	return T(math.Round(float64(f)*pow10N) / pow10N)
 }
+
+// Truncate returns the float32/float64 of the specified precision
+func Truncate[T float64 | float32](f T, n ...int) T {
+	var nn = 3
+	if len(n) > 0 {
+		nnn := n[0]
+		if nnn >= 0 {
+			nn = nnn
+			if nn > 15 {
+				nn = 15
+			}
+		}
+	}
+	pow10N := math.Pow10(nn)
+	return T(math.Floor(float64(f)*pow10N) / pow10N)
+}

math_example_test.go

@@ -101,3 +101,20 @@ func ExampleRound() {
 	// 1.235
 	// 1.23456
 }
+
+func ExampleTruncate() {
+	result1 := Truncate(1.23456)
+	result2 := Truncate(1.23456, 2)
+	result3 := Truncate(1.23456, 4)
+	result4 := Truncate(1.23456, 7)
+
+	fmt.Printf("%v\n", result1)
+	fmt.Printf("%v\n", result2)
+	fmt.Printf("%v\n", result3)
+	fmt.Printf("%v\n", result4)
+	// Output:
+	// 1.234
+	// 1.23
+	// 1.2345
+	// 1.23456
+}

math_test.go

@@ -152,3 +152,28 @@ func TestRound(t *testing.T) {
 	is.Equal(result8, 1.0)
 	is.Equal(result9, 1.0)
 }
+
+func TestTruncate(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	result1 := Truncate(0.086990000031, 5)
+	result2 := Truncate(1.23456)
+	result3 := Truncate(1.23456, 2)
+	result4 := Truncate(1.23456, 3)
+	result5 := Truncate(1.23456, 7)
+	result6 := Truncate(1.23456, 16)
+	result7 := Truncate(1.23456, -1)
+	result8 := Truncate(1.23456, 0)
+	result9 := Truncate(1.00000000001, 5)
+
+	is.Equal(result1, 0.08699)
+	is.Equal(result2, 1.234)
+	is.Equal(result3, 1.23)
+	is.Equal(result4, 1.234)
+	is.Equal(result5, 1.23456)
+	is.Equal(result6, 1.23456)
+	is.Equal(result7, 1.234)
+	is.Equal(result8, 1.0)
+	is.Equal(result9, 1.0)
+}