Remove unnecessary decimal rescaling - memory usage optimization (#160)

* Remove unnecessary decimal rescaling

* Move benchmarks to separate file, add new benchmark tests

decimal.go

@@ -390,6 +390,14 @@ func NewFromFloatWithExponent(value float64, exp int32) Decimal {
 //
 func (d Decimal) rescale(exp int32) Decimal {
 	d.ensureInitialized()
+
+	if d.exp == exp {
+		return Decimal{
+			new(big.Int).Set(d.value),
+			d.exp,
+		}
+	}
+
 	// NOTE(vadim): must convert exps to float64 before - to prevent overflow
 	diff := math.Abs(float64(exp) - float64(d.exp))
 	value := new(big.Int).Set(d.value)
@@ -419,27 +427,23 @@ func (d Decimal) Abs() Decimal {
 
 // Add returns d + d2.
 func (d Decimal) Add(d2 Decimal) Decimal {
-	baseScale := min(d.exp, d2.exp)
-	rd := d.rescale(baseScale)
-	rd2 := d2.rescale(baseScale)
+	rd, rd2 := RescalePair(d, d2)
 
 	d3Value := new(big.Int).Add(rd.value, rd2.value)
 	return Decimal{
 		value: d3Value,
-		exp:   baseScale,
+		exp:   rd.exp,
 	}
 }
 
 // Sub returns d - d2.
 func (d Decimal) Sub(d2 Decimal) Decimal {
-	baseScale := min(d.exp, d2.exp)
-	rd := d.rescale(baseScale)
-	rd2 := d2.rescale(baseScale)
+	rd, rd2 := RescalePair(d, d2)
 
 	d3Value := new(big.Int).Sub(rd.value, rd2.value)
 	return Decimal{
 		value: d3Value,
-		exp:   baseScale,
+		exp:   rd.exp,
 	}
 }
 
@@ -600,9 +604,7 @@ func (d Decimal) Cmp(d2 Decimal) int {
 		return d.value.Cmp(d2.value)
 	}
 
-	baseExp := min(d.exp, d2.exp)
-	rd := d.rescale(baseExp)
-	rd2 := d2.rescale(baseExp)
+	rd, rd2 := RescalePair(d, d2)
 
 	return rd.value.Cmp(rd2.value)
 }
@@ -1172,6 +1174,22 @@ func Avg(first Decimal, rest ...Decimal) Decimal {
 	return sum.Div(count)
 }
 
+// Rescale two decimals to common exponential value (minimal exp of both decimals)
+func RescalePair(d1 Decimal, d2 Decimal) (Decimal, Decimal) {
+	d1.ensureInitialized()
+	d2.ensureInitialized()
+
+	if d1.exp == d2.exp {
+		return d1, d2
+	}
+
+	baseScale := min(d1.exp, d2.exp)
+	if baseScale != d1.exp {
+		return d1.rescale(baseScale), d2
+	}
+	return d1, d2.rescale(baseScale)
+}
+
 func min(x, y int32) int32 {
 	if x >= y {
 		return y

decimal_bench_test.go

@@ -0,0 +1,185 @@
+package decimal
+
+import (
+	"math"
+	"math/rand"
+	"sort"
+	"strconv"
+	"testing"
+)
+
+type DecimalSlice []Decimal
+
+func (p DecimalSlice) Len() int           { return len(p) }
+func (p DecimalSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p DecimalSlice) Less(i, j int) bool { return p[i].Cmp(p[j]) < 0 }
+
+func BenchmarkNewFromFloatWithExponent(b *testing.B) {
+	rng := rand.New(rand.NewSource(0xdead1337))
+	in := make([]float64, b.N)
+	for i := range in {
+		in[i] = rng.NormFloat64() * 10e20
+	}
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		in := rng.NormFloat64() * 10e20
+		_ = NewFromFloatWithExponent(in, math.MinInt32)
+	}
+}
+
+func BenchmarkNewFromFloat(b *testing.B) {
+	rng := rand.New(rand.NewSource(0xdead1337))
+	in := make([]float64, b.N)
+	for i := range in {
+		in[i] = rng.NormFloat64() * 10e20
+	}
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		_ = NewFromFloat(in[i])
+	}
+}
+
+func BenchmarkNewFromStringFloat(b *testing.B) {
+	rng := rand.New(rand.NewSource(0xdead1337))
+	in := make([]float64, b.N)
+	for i := range in {
+		in[i] = rng.NormFloat64() * 10e20
+	}
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		in := strconv.FormatFloat(in[i], 'f', -1, 64)
+		_, _ = NewFromString(in)
+	}
+}
+
+func Benchmark_FloorFast(b *testing.B) {
+	input := New(200, 2)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		input.Floor()
+	}
+}
+
+func Benchmark_FloorRegular(b *testing.B) {
+	input := New(200, -2)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		input.Floor()
+	}
+}
+
+func Benchmark_DivideOriginal(b *testing.B) {
+	tcs := createDivTestCases()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for _, tc := range tcs {
+			d := tc.d
+			if sign(tc.d2) == 0 {
+				continue
+			}
+			d2 := tc.d2
+			prec := tc.prec
+			a := d.DivOld(d2, int(prec))
+			if sign(a) > 2 {
+				panic("dummy panic")
+			}
+		}
+	}
+}
+
+func Benchmark_DivideNew(b *testing.B) {
+	tcs := createDivTestCases()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for _, tc := range tcs {
+			d := tc.d
+			if sign(tc.d2) == 0 {
+				continue
+			}
+			d2 := tc.d2
+			prec := tc.prec
+			a := d.DivRound(d2, prec)
+			if sign(a) > 2 {
+				panic("dummy panic")
+			}
+		}
+	}
+}
+
+func BenchmarkDecimal_RoundCash_Five(b *testing.B) {
+	const want = "3.50"
+	for i := 0; i < b.N; i++ {
+		val := New(3478, -3)
+		if have := val.StringFixedCash(5); have != want {
+			b.Fatalf("\nHave: %q\nWant: %q", have, want)
+		}
+	}
+}
+
+func BenchmarkDecimal_RoundCash_Fifteen(b *testing.B) {
+	const want = "6.30"
+	for i := 0; i < b.N; i++ {
+		val := New(635, -2)
+		if have := val.StringFixedCash(15); have != want {
+			b.Fatalf("\nHave: %q\nWant: %q", have, want)
+		}
+	}
+}
+
+func Benchmark_Cmp(b *testing.B) {
+	decimals := DecimalSlice([]Decimal{})
+	for i := 0; i < 1000000; i++ {
+		decimals = append(decimals, New(int64(i), 0))
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		sort.Sort(decimals)
+	}
+}
+
+func Benchmark_decimal_Decimal_Add_different_precision(b *testing.B) {
+	d1 := NewFromFloat(1000.123)
+	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
+
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		d1.Add(d2)
+	}
+}
+
+func Benchmark_decimal_Decimal_Sub_different_precision(b *testing.B) {
+	d1 := NewFromFloat(1000.123)
+	d2 := NewFromFloat(500).Mul(NewFromFloat(0.12))
+
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		d1.Sub(d2)
+	}
+}
+
+func Benchmark_decimal_Decimal_Add_same_precision(b *testing.B) {
+	d1 := NewFromFloat(1000.123)
+	d2 := NewFromFloat(500.123)
+
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		d1.Add(d2)
+	}
+}
+
+func Benchmark_decimal_Decimal_Sub_same_precision(b *testing.B) {
+	d1 := NewFromFloat(1000.123)
+	d2 := NewFromFloat(500.123)
+
+	b.ReportAllocs()
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		d1.Add(d2)
+	}
+}

decimal_test.go

@@ -9,7 +9,6 @@ import (
 	"math/big"
 	"math/rand"
 	"reflect"
-	"sort"
 	"strconv"
 	"strings"
 	"testing"
@@ -201,47 +200,6 @@ func TestNewFromFloat32Quick(t *testing.T) {
 	}
 }
 
-func BenchmarkNewFromFloatWithExponent(b *testing.B) {
-	rng := rand.New(rand.NewSource(0xdead1337))
-	in := make([]float64, b.N)
-	for i := range in {
-		in[i] = rng.NormFloat64() * 10e20
-	}
-	b.ReportAllocs()
-	b.StartTimer()
-	for i := 0; i < b.N; i++ {
-		in := rng.NormFloat64() * 10e20
-		_ = NewFromFloatWithExponent(in, math.MinInt32)
-	}
-}
-
-func BenchmarkNewFromFloat(b *testing.B) {
-	rng := rand.New(rand.NewSource(0xdead1337))
-	in := make([]float64, b.N)
-	for i := range in {
-		in[i] = rng.NormFloat64() * 10e20
-	}
-	b.ReportAllocs()
-	b.StartTimer()
-	for i := 0; i < b.N; i++ {
-		_ = NewFromFloat(in[i])
-	}
-}
-
-func BenchmarkNewFromStringFloat(b *testing.B) {
-	rng := rand.New(rand.NewSource(0xdead1337))
-	in := make([]float64, b.N)
-	for i := range in {
-		in[i] = rng.NormFloat64() * 10e20
-	}
-	b.ReportAllocs()
-	b.StartTimer()
-	for i := 0; i < b.N; i++ {
-		in := strconv.FormatFloat(in[i], 'f', -1, 64)
-		_, _ = NewFromString(in)
-	}
-}
-
 func TestNewFromString(t *testing.T) {
 	for _, x := range testTable {
 		s := x.short
@@ -862,22 +820,6 @@ func TestDecimal_Floor(t *testing.T) {
 	}
 }
 
-func Benchmark_FloorFast(b *testing.B) {
-	input := New(200, 2)
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		input.Floor()
-	}
-}
-
-func Benchmark_FloorRegular(b *testing.B) {
-	input := New(200, -2)
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		input.Floor()
-	}
-}
-
 func TestDecimal_Ceil(t *testing.T) {
 	assertCeil := func(input, expected Decimal) {
 		got := input.Ceil()
@@ -1525,44 +1467,6 @@ func (d Decimal) DivOld(d2 Decimal, prec int) Decimal {
 	return ret
 }
 
-func Benchmark_DivideOriginal(b *testing.B) {
-	tcs := createDivTestCases()
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		for _, tc := range tcs {
-			d := tc.d
-			if sign(tc.d2) == 0 {
-				continue
-			}
-			d2 := tc.d2
-			prec := tc.prec
-			a := d.DivOld(d2, int(prec))
-			if sign(a) > 2 {
-				panic("dummy panic")
-			}
-		}
-	}
-}
-
-func Benchmark_DivideNew(b *testing.B) {
-	tcs := createDivTestCases()
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		for _, tc := range tcs {
-			d := tc.d
-			if sign(tc.d2) == 0 {
-				continue
-			}
-			d2 := tc.d2
-			prec := tc.prec
-			a := d.DivRound(d2, prec)
-			if sign(a) > 2 {
-				panic("dummy panic")
-			}
-		}
-	}
-}
-
 func sign(d Decimal) int {
 	return d.value.Sign()
 }
@@ -1719,26 +1623,6 @@ func TestDecimal_RoundCash_Panic(t *testing.T) {
 	d.RoundCash(231)
 }
 
-func BenchmarkDecimal_RoundCash_Five(b *testing.B) {
-	const want = "3.50"
-	for i := 0; i < b.N; i++ {
-		val := New(3478, -3)
-		if have := val.StringFixedCash(5); have != want {
-			b.Fatalf("\nHave: %q\nWant: %q", have, want)
-		}
-	}
-}
-
-func BenchmarkDecimal_RoundCash_Fifteen(b *testing.B) {
-	const want = "6.30"
-	for i := 0; i < b.N; i++ {
-		val := New(635, -2)
-		if have := val.StringFixedCash(15); have != want {
-			b.Fatalf("\nHave: %q\nWant: %q", have, want)
-		}
-	}
-}
-
 func TestDecimal_Mod(t *testing.T) {
 	type Inp struct {
 		a string
@@ -2193,22 +2077,6 @@ func TestDecimal_Coefficient(t *testing.T) {
 	}
 }
 
-type DecimalSlice []Decimal
-
-func (p DecimalSlice) Len() int           { return len(p) }
-func (p DecimalSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
-func (p DecimalSlice) Less(i, j int) bool { return p[i].Cmp(p[j]) < 0 }
-func Benchmark_Cmp(b *testing.B) {
-	decimals := DecimalSlice([]Decimal{})
-	for i := 0; i < 1000000; i++ {
-		decimals = append(decimals, New(int64(i), 0))
-	}
-	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
-		sort.Sort(decimals)
-	}
-}
-
 func TestNullDecimal_Scan(t *testing.T) {
 	// test the Scan method that implements the
 	// sql.Scanner interface