Merge 6e54f647f0 into 0e69d5cd53

.github/workflows/ci.yml

@@ -1,5 +1,9 @@
 name: ci
-on: [push]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 jobs:
   ci-job:
     runs-on: ubuntu-latest

decimal.go

@@ -65,6 +65,14 @@ var PowPrecisionNegativeExponent = 16
 // silently lose precision.
 var MarshalJSONWithoutQuotes = false
 
+// StringTrimTrailingZeros should be set to false if you want the decimal stringify without zeros trailing.
+// By default, when decimal is output as a string (for example, in JSON), zeros are truncated from it (2.00 -> 2, 3.11 -> 3.11, 13.000 -> 13).
+// But this logic can be changed by this variable.
+// For example, if you have numeric(10,2) values stored in your database,
+// and you want your API response to always be given 2 decimal places (even 2.00, 3.00, 17.00 [not 2,3,17]),
+// then this variable is a great way out.
+var StringTrimTrailingZeros = true
+
 // ExpMaxIterations specifies the maximum number of iterations needed to calculate
 // precise natural exponent value using ExpHullAbrham method.
 var ExpMaxIterations = 1000
@@ -1224,14 +1232,33 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
 }
 
 // NumDigits returns the number of digits of the decimal coefficient (d.Value)
-// Note: Current implementation is extremely slow for large decimals and/or decimals with large fractional part
 func (d Decimal) NumDigits() int {
-	d.ensureInitialized()
-	// Note(mwoss): It can be optimized, unnecessary cast of big.Int to string
-	if d.IsNegative() {
-		return len(d.value.String()) - 1
+	if d.value == nil {
+		return 1
 	}
-	return len(d.value.String())
+
+	if d.value.IsInt64() {
+		i64 := d.value.Int64()
+		// restrict fast path to integers with exact conversion to float64
+		if i64 <= (1<<53) && i64 >= -(1<<53) {
+			if i64 == 0 {
+				return 1
+			}
+			return int(math.Log10(math.Abs(float64(i64)))) + 1
+		}
+	}
+
+	estimatedNumDigits := int(float64(d.value.BitLen()) / math.Log2(10))
+
+	// estimatedNumDigits (lg10) may be off by 1, need to verify
+	digitsBigInt := big.NewInt(int64(estimatedNumDigits))
+	errorCorrectionUnit := digitsBigInt.Exp(tenInt, digitsBigInt, nil)
+
+	if d.value.CmpAbs(errorCorrectionUnit) >= 0 {
+		return estimatedNumDigits + 1
+	}
+
+	return estimatedNumDigits
 }
 
 // IsInteger returns true when decimal can be represented as an integer value, otherwise, it returns false.
@@ -1440,7 +1467,7 @@ func (d Decimal) InexactFloat64() float64 {
 //
 //	-12.345
 func (d Decimal) String() string {
-	return d.string(true)
+	return d.string(StringTrimTrailingZeros)
 }
 
 // StringFixed returns a rounded fixed-point string with places digits after

decimal_bench_test.go

@@ -121,6 +121,34 @@ func BenchmarkDecimal_RoundCash_Five(b *testing.B) {
 	}
 }
 
+func numDigits(b *testing.B, want int, val Decimal) {
+	b.Helper()
+	for i := 0; i < b.N; i++ {
+		if have := val.NumDigits(); have != want {
+			b.Fatalf("\nHave: %d\nWant: %d", have, want)
+		}
+	}
+}
+
+func BenchmarkDecimal_NumDigits10(b *testing.B) {
+	numDigits(b, 10, New(3478512345, -3))
+}
+
+func BenchmarkDecimal_NumDigits100(b *testing.B) {
+	s := make([]byte, 102)
+	for i := range s {
+		s[i] = byte('0' + i%10)
+	}
+	s[0] = '-'
+	s[100] = '.'
+	d, err := NewFromString(string(s))
+	if err != nil {
+		b.Log(d)
+		b.Error(err)
+	}
+	numDigits(b, 100, d)
+}
+
 func Benchmark_Cmp(b *testing.B) {
 	decimals := DecimalSlice([]Decimal{})
 	for i := 0; i < 1000000; i++ {
@@ -132,7 +160,7 @@ func Benchmark_Cmp(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Add_different_precision(b *testing.B) {
+func BenchmarkDecimal_Add_different_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
 
@@ -143,7 +171,7 @@ func Benchmark_decimal_Decimal_Add_different_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Sub_different_precision(b *testing.B) {
+func BenchmarkDecimal_Sub_different_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
 
@@ -154,7 +182,7 @@ func Benchmark_decimal_Decimal_Sub_different_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Add_same_precision(b *testing.B) {
+func BenchmarkDecimal_Add_same_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500.123)
 
@@ -165,7 +193,7 @@ func Benchmark_decimal_Decimal_Add_same_precision(b *testing.B) {
 	}
 }
 
-func Benchmark_decimal_Decimal_Sub_same_precision(b *testing.B) {
+func BenchmarkDecimal_Sub_same_precision(b *testing.B) {
 	d1 := NewFromFloat(1000.123)
 	d2 := NewFromFloat(500.123)
 

decimal_test.go

@@ -3673,3 +3673,48 @@ func ExampleNewFromFloat() {
 	//0.123123123123123
 	//-10000000000000
 }
+
+func TestDecimal_String(t *testing.T) {
+	type testData struct {
+		input string
+		expected string
+	}
+
+	tests := []testData{
+		{"1.22", "1.22"},
+		{"1.00", "1"},
+		{"153.192", "153.192"},
+		{"999.999", "999.999"},
+		{"0.0000000001", "0.0000000001"},
+		{"0.0000000000", "0"},
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input);
+		if err != nil {
+			t.Fatal(err)
+		} else if d.String() != test.expected {
+			t.Errorf("expected %s, got %s", test.expected, d.String())
+		}
+	}
+
+	defer func() {
+		StringTrimTrailingZeros = true
+	}()
+
+	StringTrimTrailingZeros = false
+	tests = []testData{
+		{"1.00", "1.00"},
+		{"0.00", "0.00"},
+		{"129.123000", "129.123000"},
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input);
+		if err != nil {
+			t.Fatal(err)
+		} else if d.String() != test.expected {
+			t.Errorf("expected %s, got %s", test.expected, d.String())
+		}
+	}
+}