chore: refactor structure

internal/number/number.go

@@ -0,0 +1,16 @@
+package number
+
+import "math"
+
+func Fixed3(num float64) float64 {
+	return fixed(num, 3)
+}
+
+func fixed(num float64, precision int) float64 {
+	output := math.Pow(10, float64(precision))
+	return float64(round(num*output)) / output
+}
+
+func round(num float64) int {
+	return int(num + math.Copysign(0.5, num))
+}

internal/number/number_test.go

@@ -0,0 +1,33 @@
+package number
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFixed(t *testing.T) {
+	for _, tc := range []struct {
+		precision        int
+		source, expected float64
+	}{
+		{3, 0, 0},
+		{3, -1, -1},
+		{3, 1.5, 1.5},
+		{3, 2.25, 2.25},
+		{3, 3.275, 3.275},
+		{3, 4.0004, 4.000},
+		{5, 5.000005, 5.00001},
+		{4, -6.00004, -6.},
+		{4, -6.00005, -6.0001},
+	} {
+		t.Run(fmt.Sprintf("%f", tc.source), func(t *testing.T) {
+			if tc.precision == 3 {
+				assert.Equal(t, tc.expected, Fixed3(tc.source))
+			} else {
+				assert.Equal(t, tc.expected, fixed(tc.source, tc.precision))
+			}
+		})
+	}
+}