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Commit 0858d884 authored by Robert Griesemer's avatar Robert Griesemer
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math/big: removed TODO, cleanups 

- factor out handling of sign
- rename bstring, pstring to fmtB, fmtP consistent with fmtE, fmtF
- move all float-to-string conversion functions into ftoa.go
- no functional changes

Change-Id: I5970ecb874dc9c387630b59147d90bda16a5d8e6
Reviewed-on: https://go-review.googlesource.com/10387Reviewed-by: default avatarAlan Donovan <adonovan@google.com>
parent acd82d50
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Showing with 152 additions and 170 deletions
src/math/big/floatconv.go
View file @ 0858d884
......@@ -2,14 +2,13 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file implements float-to-string conversion functions.
// This file implements string-to-Float conversion functions.
package big
import (
"fmt"
"io"
"strconv"
"strings"
)
......@@ -244,136 +243,3 @@ func ScanFloat(r io.ByteScanner, base int, prec uint, mode RoundingMode) (f *Flo
func ParseFloat(s string, base int, prec uint, mode RoundingMode) (f *Float, b int, err error) {
return new(Float).SetPrec(prec).SetMode(mode).Parse(s, base)
}
// 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, 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
// 'b' -ddddddp±dd, binary exponent
// 'p' -0x.dddp±dd, binary exponent, hexadecimal mantissa
//
// For the binary exponent formats, the mantissa is printed in normalized form:
//
// 'b' decimal integer mantissa using x.Prec() bits, or -0
// 'p' hexadecimal fraction with 0.5 <= 0.mantissa < 1.0, or -0
//
// The precision prec controls the number of digits (excluding the exponent)
// printed by the 'e', 'E', 'f', 'g', and 'G' formats. For 'e', 'E', and 'f'
// it is the number of digits after the decimal point. For 'g' and 'G' it is
// the total number of digits. A negative precision selects the smallest
// number of digits necessary such that ParseFloat will return f exactly.
// The prec value is ignored for the 'b' or 'p' format.
//
// BUG(gri) Float.Format does not accept negative precisions.
// BUG(gri) The Float.Format signature conflicts with Format(f fmt.State, c rune).
// (https://github.com/golang/go/issues/10938)
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))
}
// 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 {
// TODO(gri) factor out handling of sign?
// Inf
if x.IsInf() {
var ch byte = '+'
if x.neg {
ch = '-'
}
buf = append(buf, ch)
return append(buf, "Inf"...)
}
// easy formats
switch format {
case 'b':
return x.bstring(buf)
case 'p':
return x.pstring(buf)
}
return x.bigFtoa(buf, format, prec)
}
// BUG(gri): Float.String uses x.Format('g', 10) rather than x.Format('g', -1).
func (x *Float) String() string {
return x.Format('g', 10)
}
// bstring appends the string of x in the format ["-"] mantissa "p" exponent
// with a decimal mantissa and a binary exponent, or ["-"] "0" if x is zero,
// and returns the extended buffer.
// The mantissa is normalized such that is uses x.Prec() bits in binary
// representation.
func (x *Float) bstring(buf []byte) []byte {
if x.neg {
buf = append(buf, '-')
}
if x.form == zero {
return append(buf, '0')
}
if debugFloat && x.form != finite {
panic("non-finite float")
}
// x != 0
// adjust mantissa to use exactly x.prec bits
m := x.mant
switch w := uint32(len(x.mant)) * _W; {
case w < x.prec:
m = nat(nil).shl(m, uint(x.prec-w))
case w > x.prec:
m = nat(nil).shr(m, uint(w-x.prec))
}
buf = append(buf, m.decimalString()...)
buf = append(buf, 'p')
e := int64(x.exp) - int64(x.prec)
if e >= 0 {
buf = append(buf, '+')
}
return strconv.AppendInt(buf, e, 10)
}
// pstring appends the string of x in the format ["-"] "0x." mantissa "p" exponent
// with a hexadecimal mantissa and a binary exponent, or ["-"] "0" if x is zero,
// ad returns the extended buffer.
// The mantissa is normalized such that 0.5 <= 0.mantissa < 1.0.
func (x *Float) pstring(buf []byte) []byte {
if x.neg {
buf = append(buf, '-')
}
if x.form == zero {
return append(buf, '0')
}
if debugFloat && x.form != finite {
panic("non-finite float")
}
// x != 0
// remove trailing 0 words early
// (no need to convert to hex 0's and trim later)
m := x.mant
i := 0
for i < len(m) && m[i] == 0 {
i++
}
m = m[i:]
buf = append(buf, "0x."...)
buf = append(buf, strings.TrimRight(x.mant.hexString(), "0")...)
buf = append(buf, 'p')
if x.exp >= 0 {
buf = append(buf, '+')
}
return strconv.AppendInt(buf, int64(x.exp), 10)
}
src/math/big/floatconv_test.go
View file @ 0858d884
......@@ -366,6 +366,7 @@ func TestFloatFormat(t *testing.T) {
// unsupported format
{"3.14", 64, 'x', 0, "%x"},
{"-3.14", 64, 'x', 0, "%x"},
} {
f, _, err := ParseFloat(test.x, 0, test.prec, ToNearestEven)
if err != nil {
......
src/math/big/ftoa.go
View file @ 0858d884
......@@ -2,34 +2,89 @@
// 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
// This file implements Float-to-string conversion functions.
// It is closely following the corresponding implementation
// in strconv/ftoa.go, but modified and simplified for Float.
package big
import "strconv"
import (
"strconv"
"strings"
)
// TODO(gri) Consider moving sign into decimal - could make the signatures below cleaner.
// 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, 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
// 'b' -ddddddp±dd, binary exponent
// 'p' -0x.dddp±dd, binary exponent, hexadecimal mantissa
//
// For the binary exponent formats, the mantissa is printed in normalized form:
//
// 'b' decimal integer mantissa using x.Prec() bits, or -0
// 'p' hexadecimal fraction with 0.5 <= 0.mantissa < 1.0, or -0
//
// The precision prec controls the number of digits (excluding the exponent)
// printed by the 'e', 'E', 'f', 'g', and 'G' formats. For 'e', 'E', and 'f'
// it is the number of digits after the decimal point. For 'g' and 'G' it is
// the total number of digits. A negative precision selects the smallest
// number of digits necessary such that ParseFloat will return f exactly.
// The prec value is ignored for the 'b' or 'p' format.
//
// BUG(gri) Float.Format does not accept negative precisions.
// BUG(gri) The Float.Format signature conflicts with Format(f fmt.State, c rune).
// (https://github.com/golang/go/issues/10938)
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))
}
// bigFtoa formats a float for the %e, %E, %f, %g, and %G formats.
func (f *Float) bigFtoa(buf []byte, fmt byte, prec int) []byte {
if debugFloat && f.IsInf() {
panic("non-finite float")
// String formats x like x.Format('g', 10).
func (x *Float) String() string {
return x.Format('g', 10)
}
// Append appends to buf the string form of the floating-point number x,
// as generated by x.Format, and returns the extended buffer.
func (x *Float) Append(buf []byte, fmt byte, prec int) []byte {
// sign
if x.neg {
buf = append(buf, '-')
}
// Inf
if x.IsInf() {
if !x.neg {
buf = append(buf, '+')
}
return append(buf, "Inf"...)
}
// pick off easy formats
switch fmt {
case 'b':
return x.fmtB(buf)
case 'p':
return x.fmtP(buf)
}
// Algorithm:
// 1) convert Float to multiprecision decimal
// 2) round to desired precision
// 3) read digits out and format
// 1) convert Float to multiprecision decimal
var mant nat
if f.form == finite {
mant = f.mant
if x.form == finite {
mant = x.mant
}
var d decimal
d.init(mant, int(f.exp)-f.mant.bitLen())
d.init(mant, int(x.exp)-x.mant.bitLen())
// 2) round to desired precision
shortest := false
......@@ -67,9 +122,9 @@ func (f *Float) bigFtoa(buf []byte, fmt byte, prec int) []byte {
// 3) read digits out and format
switch fmt {
case 'e', 'E':
return fmtE(buf, fmt, prec, f.neg, d)
return fmtE(buf, fmt, prec, d)
case 'f':
return fmtF(buf, prec, f.neg, d)
return fmtF(buf, prec, d)
case 'g', 'G':
// trim trailing fractional zeros in %e format
eprec := prec
......@@ -88,25 +143,23 @@ func (f *Float) bigFtoa(buf []byte, fmt byte, prec int) []byte {
if prec > len(d.mant) {
prec = len(d.mant)
}
return fmtE(buf, fmt+'e'-'g', prec-1, f.neg, d)
return fmtE(buf, fmt+'e'-'g', prec-1, d)
}
if prec > d.exp {
prec = len(d.mant)
}
return fmtF(buf, max(prec-d.exp, 0), f.neg, d)
return fmtF(buf, max(prec-d.exp, 0), d)
}
// unknown format
if x.neg {
buf = buf[:len(buf)-1] // sign was added prematurely - remove it again
}
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, '-')
}
// %e: d.ddddde±dd
func fmtE(buf []byte, fmt byte, prec int, d decimal) []byte {
// first digit
ch := byte('0')
if len(d.mant) > 0 {
......@@ -149,13 +202,8 @@ func fmtE(buf []byte, fmt byte, prec int, neg bool, d decimal) []byte {
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, '-')
}
// %f: ddddddd.ddddd
func fmtF(buf []byte, prec int, d decimal) []byte {
// integer, padded with zeros as needed
if d.exp > 0 {
m := min(len(d.mant), d.exp)
......@@ -182,6 +230,73 @@ func fmtF(buf []byte, prec int, neg bool, d decimal) []byte {
return buf
}
// fmtB appends the string of x in the format mantissa "p" exponent
// with a decimal mantissa and a binary exponent, or 0" if x is zero,
// and returns the extended buffer.
// The mantissa is normalized such that is uses x.Prec() bits in binary
// representation.
// The sign of x is ignored, and x must not be an Inf.
func (x *Float) fmtB(buf []byte) []byte {
if x.form == zero {
return append(buf, '0')
}
if debugFloat && x.form != finite {
panic("non-finite float")
}
// x != 0
// adjust mantissa to use exactly x.prec bits
m := x.mant
switch w := uint32(len(x.mant)) * _W; {
case w < x.prec:
m = nat(nil).shl(m, uint(x.prec-w))
case w > x.prec:
m = nat(nil).shr(m, uint(w-x.prec))
}
buf = append(buf, m.decimalString()...)
buf = append(buf, 'p')
e := int64(x.exp) - int64(x.prec)
if e >= 0 {
buf = append(buf, '+')
}
return strconv.AppendInt(buf, e, 10)
}
// fmtP appends the string of x in the format 0x." mantissa "p" exponent
// with a hexadecimal mantissa and a binary exponent, or 0" if x is zero,
// ad returns the extended buffer.
// The mantissa is normalized such that 0.5 <= 0.mantissa < 1.0.
// The sign of x is ignored, and x must not be an Inf.
func (x *Float) fmtP(buf []byte) []byte {
if x.form == zero {
return append(buf, '0')
}
if debugFloat && x.form != finite {
panic("non-finite float")
}
// x != 0
// remove trailing 0 words early
// (no need to convert to hex 0's and trim later)
m := x.mant
i := 0
for i < len(m) && m[i] == 0 {
i++
}
m = m[i:]
buf = append(buf, "0x."...)
buf = append(buf, strings.TrimRight(x.mant.hexString(), "0")...)
buf = append(buf, 'p')
if x.exp >= 0 {
buf = append(buf, '+')
}
return strconv.AppendInt(buf, int64(x.exp), 10)
}
func min(x, y int) int {
if x < y {
return x
......
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