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Commit 721d5893 authored by Robert Griesemer's avatar Robert Griesemer
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math/big: first version of Float %e, %f, %g, %G formatting working 

Change-Id: I10efa3bc8bc7f41100feabe17837f805a42d7eb6
Reviewed-on: https://go-review.googlesource.com/3842Reviewed-by: default avatarAlan Donovan <adonovan@google.com>
parent b8fcae02
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Showing with 329 additions and 26 deletions
src/math/big/floatconv.go
View file @ 721d5893
......@@ -162,8 +162,8 @@ func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b i
// Format converts the floating-point number x to a string according
// to the given format and precision prec. The format is one of:
//
// 'e' -d.dddde±dd, decimal exponent
// 'E' -d.ddddE±dd, decimal exponent
// 'e' -d.dddde±dd, decimal exponent, at least two (possibly 0) exponent digits
// 'E' -d.ddddE±dd, decimal exponent, at least two (possibly 0) exponent digits
// 'f' -ddddd.dddd, no exponent
// 'g' like 'e' for large exponents, like 'f' otherwise
// 'G' like 'E' for large exponents, like 'f' otherwise
......@@ -182,7 +182,7 @@ func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b i
// number of digits necessary such that ParseFloat will return f exactly.
// The prec value is ignored for the 'b' or 'p' format.
//
// BUG(gri) Currently, Format only accepts the 'b' and 'p' format.
// BUG(gri) Currently, Format does not accept negative precisions.
func (x *Float) Format(format byte, prec int) string {
const extra = 10 // TODO(gri) determine a good/better value here
return string(x.Append(make([]byte, 0, prec+extra), format, prec))
......@@ -191,13 +191,14 @@ func (x *Float) Format(format byte, prec int) string {
// Append appends the string form of the floating-point number x,
// as generated by x.Format, to buf and returns the extended buffer.
func (x *Float) Append(buf []byte, format byte, prec int) []byte {
// pick off simple cases
switch format {
case 'b':
return x.bstring(buf)
case 'p':
return x.pstring(buf)
}
return append(buf, fmt.Sprintf(`%%!c`, format)...)
return x.bigFtoa(buf, format, prec)
}
// BUG(gri): Currently, String uses the 'p' (rather than 'g') format.
......
src/math/big/floatconv_test.go
View file @ 721d5893
......@@ -5,6 +5,7 @@
package big
import (
"math"
"strconv"
"testing"
)
......@@ -71,37 +72,157 @@ func TestFloatSetFloat64String(t *testing.T) {
}
}
func TestFloatFormat(t *testing.T) {
const (
below1e23 = 99999999999999974834176
above1e23 = 100000000000000008388608
)
func TestFloat64Format(t *testing.T) {
for _, test := range []struct {
x string
x float64
format byte
prec int
want string
}{
{"0", 'b', 0, "0"},
{"-0", 'b', 0, "-0"},
{"1.0", 'b', 0, "4503599627370496p-52"},
{"-1.0", 'b', 0, "-4503599627370496p-52"},
{"4503599627370496", 'b', 0, "4503599627370496p+0"},
{"0", 'p', 0, "0"},
{"-0", 'p', 0, "-0"},
{"1024.0", 'p', 0, "0x.8p11"},
{"-1024.0", 'p', 0, "-0x.8p11"},
} {
f64, err := strconv.ParseFloat(test.x, 64)
if err != nil {
t.Error(err)
continue
}
{0, 'f', 0, "0"},
{math.Copysign(0, -1), 'f', 0, "-0"},
{1, 'f', 0, "1"},
{-1, 'f', 0, "-1"},
{1.459, 'e', 0, "1e+00"},
{2.459, 'e', 1, "2.5e+00"},
{3.459, 'e', 2, "3.46e+00"},
{4.459, 'e', 3, "4.459e+00"},
{5.459, 'e', 4, "5.4590e+00"},
{1.459, 'f', 0, "1"},
{2.459, 'f', 1, "2.5"},
{3.459, 'f', 2, "3.46"},
{4.459, 'f', 3, "4.459"},
{5.459, 'f', 4, "5.4590"},
{0, 'b', 0, "0"},
{math.Copysign(0, -1), 'b', 0, "-0"},
{1.0, 'b', 0, "4503599627370496p-52"},
{-1.0, 'b', 0, "-4503599627370496p-52"},
{4503599627370496, 'b', 0, "4503599627370496p+0"},
{0, 'p', 0, "0"},
{math.Copysign(0, -1), 'p', 0, "-0"},
{1024.0, 'p', 0, "0x.8p11"},
{-1024.0, 'p', 0, "-0x.8p11"},
// all test cases below from strconv/ftoa_test.go
{1, 'e', 5, "1.00000e+00"},
{1, 'f', 5, "1.00000"},
{1, 'g', 5, "1"},
// {1, 'g', -1, "1"},
// {20, 'g', -1, "20"},
// {1234567.8, 'g', -1, "1.2345678e+06"},
// {200000, 'g', -1, "200000"},
// {2000000, 'g', -1, "2e+06"},
// g conversion and zero suppression
{400, 'g', 2, "4e+02"},
{40, 'g', 2, "40"},
{4, 'g', 2, "4"},
{.4, 'g', 2, "0.4"},
{.04, 'g', 2, "0.04"},
{.004, 'g', 2, "0.004"},
{.0004, 'g', 2, "0.0004"},
{.00004, 'g', 2, "4e-05"},
{.000004, 'g', 2, "4e-06"},
{0, 'e', 5, "0.00000e+00"},
{0, 'f', 5, "0.00000"},
{0, 'g', 5, "0"},
// {0, 'g', -1, "0"},
{-1, 'e', 5, "-1.00000e+00"},
{-1, 'f', 5, "-1.00000"},
{-1, 'g', 5, "-1"},
// {-1, 'g', -1, "-1"},
{12, 'e', 5, "1.20000e+01"},
{12, 'f', 5, "12.00000"},
{12, 'g', 5, "12"},
// {12, 'g', -1, "12"},
{123456700, 'e', 5, "1.23457e+08"},
{123456700, 'f', 5, "123456700.00000"},
{123456700, 'g', 5, "1.2346e+08"},
// {123456700, 'g', -1, "1.234567e+08"},
f := new(Float).SetFloat64(f64)
{1.2345e6, 'e', 5, "1.23450e+06"},
{1.2345e6, 'f', 5, "1234500.00000"},
{1.2345e6, 'g', 5, "1.2345e+06"},
{1e23, 'e', 17, "9.99999999999999916e+22"},
{1e23, 'f', 17, "99999999999999991611392.00000000000000000"},
{1e23, 'g', 17, "9.9999999999999992e+22"},
// {1e23, 'e', -1, "1e+23"},
// {1e23, 'f', -1, "100000000000000000000000"},
// {1e23, 'g', -1, "1e+23"},
{below1e23, 'e', 17, "9.99999999999999748e+22"},
{below1e23, 'f', 17, "99999999999999974834176.00000000000000000"},
// {below1e23, 'g', 17, "9.9999999999999975e+22"},
// {below1e23, 'e', -1, "9.999999999999997e+22"},
// {below1e23, 'f', -1, "99999999999999970000000"},
// {below1e23, 'g', -1, "9.999999999999997e+22"},
{above1e23, 'e', 17, "1.00000000000000008e+23"},
{above1e23, 'f', 17, "100000000000000008388608.00000000000000000"},
// {above1e23, 'g', 17, "1.0000000000000001e+23"},
// {above1e23, 'e', -1, "1.0000000000000001e+23"},
// {above1e23, 'f', -1, "100000000000000010000000"},
// {above1e23, 'g', -1, "1.0000000000000001e+23"},
// {fdiv(5e-304, 1e20), 'g', -1, "5e-324"},
// {fdiv(-5e-304, 1e20), 'g', -1, "-5e-324"},
// {32, 'g', -1, "32"},
// {32, 'g', 0, "3e+01"},
// {100, 'x', -1, "%x"},
// {math.NaN(), 'g', -1, "NaN"},
// {-math.NaN(), 'g', -1, "NaN"},
// {math.Inf(0), 'g', -1, "+Inf"},
// {math.Inf(-1), 'g', -1, "-Inf"},
// {-math.Inf(0), 'g', -1, "-Inf"},
{-1, 'b', -1, "-4503599627370496p-52"},
// fixed bugs
{0.9, 'f', 1, "0.9"},
{0.09, 'f', 1, "0.1"},
{0.0999, 'f', 1, "0.1"},
{0.05, 'f', 1, "0.1"},
{0.05, 'f', 0, "0"},
{0.5, 'f', 1, "0.5"},
{0.5, 'f', 0, "0"},
{1.5, 'f', 0, "2"},
// http://www.exploringbinary.com/java-hangs-when-converting-2-2250738585072012e-308/
// {2.2250738585072012e-308, 'g', -1, "2.2250738585072014e-308"},
// http://www.exploringbinary.com/php-hangs-on-numeric-value-2-2250738585072011e-308/
// {2.2250738585072011e-308, 'g', -1, "2.225073858507201e-308"},
// Issue 2625.
{383260575764816448, 'f', 0, "383260575764816448"},
// {383260575764816448, 'g', -1, "3.8326057576481645e+17"},
} {
f := new(Float).SetFloat64(test.x)
got := f.Format(test.format, test.prec)
if got != test.want {
t.Errorf("%v: got %s; want %s", test, got, test.want)
}
if test.format == 'b' && f64 == 0 {
if test.format == 'b' && test.x == 0 {
continue // 'b' format in strconv.Float requires knowledge of bias for 0.0
}
if test.format == 'p' {
......@@ -109,9 +230,9 @@ func TestFloatFormat(t *testing.T) {
}
// verify that Float format matches strconv format
want := strconv.FormatFloat(f64, test.format, test.prec, 64)
want := strconv.FormatFloat(test.x, test.format, test.prec, 64)
if got != want {
t.Errorf("%v: got %s; want %s", test, got, want)
t.Errorf("%v: got %s; want %s (strconv)", test, got, want)
}
}
}
src/math/big/ftoa.go 0 → 100644
View file @ 721d5893
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements the 'e', 'f', 'g' floating-point formats.
// It is closely following the corresponding implementation in
// strconv/ftoa.go, but modified and simplified for big.Float.
// Algorithm:
// 1) convert Float to multiprecision decimal
// 2) round to desired precision
// 3) read digits out and format
package big
import "strconv"
// TODO(gri) Consider moving sign into decimal - could make the signatures below cleaner.
// bigFtoa formats a float for the %e, %E, %f, %g, and %G formats.
func (f *Float) bigFtoa(buf []byte, fmt byte, prec int) []byte {
// TODO(gri) handle Inf.
// 1) convert Float to multiprecision decimal
var d decimal
d.init(f.mant, int(f.exp)-f.mant.bitLen())
// 2) round to desired precision
shortest := false
if prec < 0 {
shortest = true
panic("unimplemented")
// TODO(gri) complete this
// roundShortest(&d, f.mant, int(f.exp))
// Precision for shortest representation mode.
switch fmt {
case 'e', 'E':
prec = len(d.mant) - 1
case 'f':
prec = max(len(d.mant)-d.exp, 0)
case 'g', 'G':
prec = len(d.mant)
}
} else {
// round appropriately
switch fmt {
case 'e', 'E':
// one digit before and number of digits after decimal point
d.round(1 + prec)
case 'f':
// number of digits before and after decimal point
d.round(d.exp + prec)
case 'g', 'G':
if prec == 0 {
prec = 1
}
d.round(prec)
}
}
// 3) read digits out and format
switch fmt {
case 'e', 'E':
return fmtE(buf, fmt, prec, f.neg, d)
case 'f':
return fmtF(buf, prec, f.neg, d)
case 'g', 'G':
// trim trailing fractional zeros in %e format
eprec := prec
if eprec > len(d.mant) && len(d.mant) >= d.exp {
eprec = len(d.mant)
}
// %e is used if the exponent from the conversion
// is less than -4 or greater than or equal to the precision.
// If precision was the shortest possible, use eprec = 6 for
// this decision.
if shortest {
eprec = 6
}
exp := d.exp - 1
if exp < -4 || exp >= eprec {
if prec > len(d.mant) {
prec = len(d.mant)
}
return fmtE(buf, fmt+'e'-'g', prec-1, f.neg, d)
}
if prec > d.exp {
prec = len(d.mant)
}
return fmtF(buf, max(prec-d.exp, 0), f.neg, d)
}
// unknown format
return append(buf, '%', fmt)
}
// %e: -d.ddddde±dd
func fmtE(buf []byte, fmt byte, prec int, neg bool, d decimal) []byte {
// sign
if neg {
buf = append(buf, '-')
}
// first digit
ch := byte('0')
if len(d.mant) > 0 {
ch = d.mant[0]
}
buf = append(buf, ch)
// .moredigits
if prec > 0 {
buf = append(buf, '.')
// TODO(gri) clean up logic below
i := 1
m := len(d.mant) + prec + 1 - max(len(d.mant), prec+1)
if i < m {
buf = append(buf, d.mant[i:m]...)
i = m
}
for ; i <= prec; i++ {
buf = append(buf, '0')
}
}
// e±
buf = append(buf, fmt)
var exp int64
if len(d.mant) > 0 {
exp = int64(d.exp) - 1 // -1 because first digit was printed before '.'
}
if exp < 0 {
ch = '-'
exp = -exp
} else {
ch = '+'
}
buf = append(buf, ch)
// dd...d
if exp < 10 {
buf = append(buf, '0') // at least 2 exponent digits
}
return strconv.AppendInt(buf, exp, 10)
}
// %f: -ddddddd.ddddd
func fmtF(buf []byte, prec int, neg bool, d decimal) []byte {
// sign
if neg {
buf = append(buf, '-')
}
// integer, padded with zeros as needed.
if d.exp > 0 {
// TODO(gri) fuse loops below and/or cleanup
var i int
for i = 0; i < int(d.exp) && i < len(d.mant); i++ {
buf = append(buf, d.mant[i])
}
for ; i < d.exp; i++ {
buf = append(buf, '0')
}
} else {
buf = append(buf, '0')
}
// fraction
if prec > 0 {
buf = append(buf, '.')
for i := 0; i < prec; i++ {
ch := byte('0')
if j := d.exp + i; 0 <= j && j < len(d.mant) {
ch = d.mant[j]
}
buf = append(buf, ch)
}
}
return buf
}
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