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Exact representation in NewFromFloat (#78)
* Additional (and some breaking) tests for NewFromFloatWithExponent * Addressing tests for NewFromFloatWithExponent * Naming cosmetic correction * removing unused code * Improving FromFloatWithExponent * Tests for exact float representation added * Exact float representation in FromFloat * Adding breaking test for NewFromFloat * Fast path in FromFloat is unreliable, fixing it * Addressing special meaning of zero exponent in float64 * NewFromFloatWithExponent: subnormals support * NewFromFloatWithExponent: just a few additional test cases * NewFromFloat: documentation update * NewFromFloatWithExponent: optimization and some documentation * NewFromFloatWithExponent: optimizations * NewFromFloatWithExponent: optimizations
This commit is contained in:
Igor Mikushkin
Victor Quinn
parent
bf9a39e28b
commit
78e9b82f68
2 changed files with 75 additions and 50 deletions
20
decimal.go
20
decimal.go
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@ -160,24 +160,12 @@ func NewFromString(value string) (Decimal, error) {
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// NewFromFloat(123.45678901234567).String() // output: "123.4567890123456"
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// NewFromFloat(.00000000000000001).String() // output: "0.00000000000000001"
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//
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// NOTE: some float64 numbers can take up about 300 bytes of memory in decimal representation.
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// Consider using NewFromFloatWithExponent if space is more important than precision.
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//
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// NOTE: this will panic on NaN, +/-inf
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func NewFromFloat(value float64) Decimal {
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floor := math.Floor(value)
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// fast path, where float is an int
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if floor == value && value <= math.MaxInt64 && value >= math.MinInt64 {
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return New(int64(value), 0)
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}
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// slow path: float is a decimal
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// HACK(vadim): do this the slow hacky way for now because the logic to
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// convert a base-2 float to base-10 properly is not trivial
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str := strconv.FormatFloat(value, 'f', -1, 64)
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dec, err := NewFromString(str)
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if err != nil {
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panic(err)
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}
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return dec
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return NewFromFloatWithExponent(value, math.MinInt32)
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}
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// NewFromFloatWithExponent converts a float64 to Decimal, with an arbitrary
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105
decimal_test.go
105
decimal_test.go
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@ -14,28 +14,35 @@ import (
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"time"
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)
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var testTable = map[float64]string{
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3.141592653589793: "3.141592653589793",
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3: "3",
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1234567890123456: "1234567890123456",
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1234567890123456000: "1234567890123456000",
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1234.567890123456: "1234.567890123456",
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.1234567890123456: "0.1234567890123456",
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0: "0",
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.1111111111111110: "0.111111111111111",
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.1111111111111111: "0.1111111111111111",
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.1111111111111119: "0.1111111111111119",
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.000000000000000001: "0.000000000000000001",
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.000000000000000002: "0.000000000000000002",
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.000000000000000003: "0.000000000000000003",
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.000000000000000005: "0.000000000000000005",
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.000000000000000008: "0.000000000000000008",
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.1000000000000001: "0.1000000000000001",
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.1000000000000002: "0.1000000000000002",
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.1000000000000003: "0.1000000000000003",
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.1000000000000005: "0.1000000000000005",
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.1000000000000008: "0.1000000000000008",
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1e25: "10000000000000000000000000",
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type testEnt struct {
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float float64
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short string
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exact string
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}
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var testTable = []*testEnt{
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{3.141592653589793, "3.141592653589793", ""},
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{3, "3", ""},
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{1234567890123456, "1234567890123456", ""},
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{1234567890123456000, "1234567890123456000", ""},
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{1234.567890123456, "1234.567890123456", ""},
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{.1234567890123456, "0.1234567890123456", ""},
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{0, "0", ""},
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{.1111111111111110, "0.111111111111111", ""},
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{.1111111111111111, "0.1111111111111111", ""},
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{.1111111111111119, "0.1111111111111119", ""},
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{.000000000000000001, "0.000000000000000001", ""},
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{.000000000000000002, "0.000000000000000002", ""},
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{.000000000000000003, "0.000000000000000003", ""},
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{.000000000000000005, "0.000000000000000005", ""},
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{.000000000000000008, "0.000000000000000008", ""},
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{.1000000000000001, "0.1000000000000001", ""},
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{.1000000000000002, "0.1000000000000002", ""},
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{.1000000000000003, "0.1000000000000003", ""},
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{.1000000000000005, "0.1000000000000005", ""},
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{.1000000000000008, "0.1000000000000008", ""},
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{1e25, "10000000000000000000000000", ""},
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{math.MaxInt64, strconv.FormatInt(math.MaxInt64, 10), ""},
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}
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var testTableScientificNotation = map[string]string{
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@ -54,12 +61,23 @@ var testTableScientificNotation = map[string]string{
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}
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func init() {
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// add negatives
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for f, s := range testTable {
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if f > 0 {
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testTable[-f] = "-" + s
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for _, s := range testTable {
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s.exact = strconv.FormatFloat(s.float, 'f', 300, 64)
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if strings.ContainsRune(s.exact, '.') {
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s.exact = strings.TrimRight(s.exact, "0")
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s.exact = strings.TrimRight(s.exact, ".")
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}
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}
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// add negatives
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withNeg := testTable[:]
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for _, s := range testTable {
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if s.float > 0 {
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withNeg = append(withNeg, &testEnt{-s.float, "-" + s.short, "-" + s.exact})
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}
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}
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testTable = withNeg
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for e, s := range testTableScientificNotation {
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if string(e[0]) != "-" && s != "0" {
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testTableScientificNotation["-"+e] = "-" + s
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@ -68,8 +86,9 @@ func init() {
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}
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func TestNewFromFloat(t *testing.T) {
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for f, s := range testTable {
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d := NewFromFloat(f)
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for _, x := range testTable {
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s := x.exact
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d := NewFromFloat(x.float)
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if d.String() != s {
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t.Errorf("expected %s, got %s (%s, %d)",
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s, d.String(),
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@ -92,7 +111,20 @@ func TestNewFromFloat(t *testing.T) {
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}
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func TestNewFromString(t *testing.T) {
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for _, s := range testTable {
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for _, x := range testTable {
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s := x.short
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d, err := NewFromString(s)
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if err != nil {
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t.Errorf("error while parsing %s", s)
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} else if d.String() != s {
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t.Errorf("expected %s, got %s (%s, %d)",
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s, d.String(),
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d.value.String(), d.exp)
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}
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}
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for _, x := range testTable {
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s := x.exact
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d, err := NewFromString(s)
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if err != nil {
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t.Errorf("error while parsing %s", s)
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@ -289,7 +321,8 @@ func TestNewFromBigIntWithExponent(t *testing.T) {
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}
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func TestJSON(t *testing.T) {
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for _, s := range testTable {
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for _, x := range testTable {
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s := x.short
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var doc struct {
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Amount Decimal `json:"amount"`
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}
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@ -358,7 +391,8 @@ func TestBadJSON(t *testing.T) {
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}
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func TestNullDecimalJSON(t *testing.T) {
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for _, s := range testTable {
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for _, x := range testTable {
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s := x.short
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var doc struct {
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Amount NullDecimal `json:"amount"`
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}
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@ -450,7 +484,8 @@ func TestNullDecimalBadJSON(t *testing.T) {
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}
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func TestXML(t *testing.T) {
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for _, s := range testTable {
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for _, x := range testTable {
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s := x.short
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var doc struct {
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XMLName xml.Name `xml:"account"`
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Amount Decimal `xml:"amount"`
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@ -2035,7 +2070,8 @@ func TestNullDecimal_Value(t *testing.T) {
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}
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func TestBinary(t *testing.T) {
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for x := range testTable {
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for _, y := range testTable {
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x := y.float
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// Create the decimal
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d1 := NewFromFloat(x)
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@ -2070,7 +2106,8 @@ func slicesEqual(a, b []byte) bool {
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}
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func TestGobEncode(t *testing.T) {
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for x := range testTable {
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for _, y := range testTable {
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x := y.float
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d1 := NewFromFloat(x)
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b1, err := d1.GobEncode()
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