Move adp.Decimal functions

artie-labs · Jun 26, 2024 · 197fd5b · 197fd5b
1 parent fd08cfd
commit 197fd5b
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Showing 3 changed files with 70 additions and 31 deletions.
diff --git a/lib/debezium/decimal_test.go b/lib/debezium/decimal_test.go
@@ -6,7 +6,7 @@ import (
 	"math/big"
 	"testing"
 
-	"github.com/cockroachdb/apd/v3"
+	"github.com/artie-labs/transfer/lib/numbers"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -41,37 +41,9 @@ func TestDecodeBigInt(t *testing.T) {
 	}
 }
 
-func mustParseDecimal(value string) *apd.Decimal {
-	decimal, _, err := apd.NewFromString(value)
-	if err != nil {
-		panic(err)
-	}
-	return decimal
-}
-
-func TestDecimalWithNewExponent(t *testing.T) {
-	assert.Equal(t, "0", decimalWithNewExponent(apd.New(0, 0), 0).Text('f'))
-	assert.Equal(t, "00", decimalWithNewExponent(apd.New(0, 1), 1).Text('f'))
-	assert.Equal(t, "0", decimalWithNewExponent(apd.New(0, 100), 0).Text('f'))
-	assert.Equal(t, "00", decimalWithNewExponent(apd.New(0, 0), 1).Text('f'))
-	assert.Equal(t, "0.0", decimalWithNewExponent(apd.New(0, 0), -1).Text('f'))
-
-	// Same exponent:
-	assert.Equal(t, "12.349", decimalWithNewExponent(mustParseDecimal("12.349"), -3).Text('f'))
-	// More precise exponent:
-	assert.Equal(t, "12.3490", decimalWithNewExponent(mustParseDecimal("12.349"), -4).Text('f'))
-	assert.Equal(t, "12.34900", decimalWithNewExponent(mustParseDecimal("12.349"), -5).Text('f'))
-	// Lest precise exponent:
-	// Extra digits should be truncated rather than rounded.
-	assert.Equal(t, "12.34", decimalWithNewExponent(mustParseDecimal("12.349"), -2).Text('f'))
-	assert.Equal(t, "12.3", decimalWithNewExponent(mustParseDecimal("12.349"), -1).Text('f'))
-	assert.Equal(t, "12", decimalWithNewExponent(mustParseDecimal("12.349"), 0).Text('f'))
-	assert.Equal(t, "10", decimalWithNewExponent(mustParseDecimal("12.349"), 1).Text('f'))
-}
-
 func TestEncodeDecimal(t *testing.T) {
 	testEncodeDecimal := func(value string, expectedScale int32) {
-		bytes, scale := EncodeDecimal(mustParseDecimal(value))
+		bytes, scale := EncodeDecimal(numbers.MustParseDecimal(value))
 		actual := DecodeDecimal(bytes, nil, int(scale)).String()
 		assert.Equal(t, value, actual, value)
 		assert.Equal(t, expectedScale, scale, value)
@@ -91,7 +63,7 @@ func TestEncodeDecimal(t *testing.T) {
 
 func TestEncodeDecimalWithScale(t *testing.T) {
 	mustEncodeAndDecodeDecimal := func(value string, scale int32) string {
-		bytes := EncodeDecimalWithScale(mustParseDecimal(value), scale)
+		bytes := EncodeDecimalWithScale(numbers.MustParseDecimal(value), scale)
 		return DecodeDecimal(bytes, nil, int(scale)).String()
 	}
 

diff --git a/lib/numbers/decimal.go b/lib/numbers/decimal.go
@@ -0,0 +1,39 @@
+package numbers
+
+import "github.com/cockroachdb/apd/v3"
+
+// MustParseDecimal parses a string to an [apd.Decimal] or panics -- used for tests.
+func MustParseDecimal(value string) *apd.Decimal {
+	decimal, _, err := apd.NewFromString(value)
+	if err != nil {
+		panic(err)
+	}
+	return decimal
+}
+
+// DecimalWithNewExponent takes a [apd.Decimal] and returns a new [apd.Decimal] with a the given exponent.
+// If the new exponent is less precise then the extra digits will be truncated.
+func DecimalWithNewExponent(decimal *apd.Decimal, newExponent int32) *apd.Decimal {
+	exponentDelta := newExponent - decimal.Exponent // Exponent is negative.
+
+	if exponentDelta == 0 {
+		return new(apd.Decimal).Set(decimal)
+	}
+
+	coefficient := new(apd.BigInt).Set(&decimal.Coeff)
+
+	if exponentDelta < 0 {
+		multiplier := new(apd.BigInt).Exp(apd.NewBigInt(10), apd.NewBigInt(int64(-exponentDelta)), nil)
+		coefficient.Mul(coefficient, multiplier)
+	} else if exponentDelta > 0 {
+		divisor := new(apd.BigInt).Exp(apd.NewBigInt(10), apd.NewBigInt(int64(exponentDelta)), nil)
+		coefficient.Div(coefficient, divisor)
+	}
+
+	return &apd.Decimal{
+		Form:     decimal.Form,
+		Negative: decimal.Negative,
+		Exponent: newExponent,
+		Coeff:    *coefficient,
+	}
+}
diff --git a/lib/numbers/decimal_test.go b/lib/numbers/decimal_test.go
@@ -0,0 +1,28 @@
+package numbers
+
+import (
+	"testing"
+
+	"github.com/cockroachdb/apd/v3"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDecimalWithNewExponent(t *testing.T) {
+	assert.Equal(t, "0", DecimalWithNewExponent(apd.New(0, 0), 0).Text('f'))
+	assert.Equal(t, "00", DecimalWithNewExponent(apd.New(0, 1), 1).Text('f'))
+	assert.Equal(t, "0", DecimalWithNewExponent(apd.New(0, 100), 0).Text('f'))
+	assert.Equal(t, "00", DecimalWithNewExponent(apd.New(0, 0), 1).Text('f'))
+	assert.Equal(t, "0.0", DecimalWithNewExponent(apd.New(0, 0), -1).Text('f'))
+
+	// Same exponent:
+	assert.Equal(t, "12.349", DecimalWithNewExponent(MustParseDecimal("12.349"), -3).Text('f'))
+	// More precise exponent:
+	assert.Equal(t, "12.3490", DecimalWithNewExponent(MustParseDecimal("12.349"), -4).Text('f'))
+	assert.Equal(t, "12.34900", DecimalWithNewExponent(MustParseDecimal("12.349"), -5).Text('f'))
+	// Lest precise exponent:
+	// Extra digits should be truncated rather than rounded.
+	assert.Equal(t, "12.34", DecimalWithNewExponent(MustParseDecimal("12.349"), -2).Text('f'))
+	assert.Equal(t, "12.3", DecimalWithNewExponent(MustParseDecimal("12.349"), -1).Text('f'))
+	assert.Equal(t, "12", DecimalWithNewExponent(MustParseDecimal("12.349"), 0).Text('f'))
+	assert.Equal(t, "10", DecimalWithNewExponent(MustParseDecimal("12.349"), 1).Text('f'))
+}