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strconv: 2x-4x speed improvement for atof64.

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benchmark                      old ns/op    new ns/op    delta
BenchmarkAtof64Decimal               344           71  -79.22%
BenchmarkAtof64Float                 397           90  -77.15%
BenchmarkAtof64FloatExp              445          241  -45.84%
BenchmarkAtof64Big                   731          324  -55.68%
BenchmarkAtof64RandomBits            761          453  -40.47%
BenchmarkAtof64RandomFloats          690          314  -54.49%

R=dave, rsc
CC=golang-dev, remy
https://golang.org/cl/5988053
This commit is contained in:
Rémy Oudompheng 2012-04-21 13:56:51 +02:00
parent dd963ddf05
commit cad480440d
3 changed files with 183 additions and 82 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

236
src/pkg/strconv/atof.go
View File

@ -37,17 +37,28 @@ func equalIgnoreCase(s1, s2 string) bool {
}
func special(s string) (f float64, ok bool) {
switch {
case equalIgnoreCase(s, "nan"):
return math.NaN(), true
case equalIgnoreCase(s, "-inf"),
equalIgnoreCase(s, "-infinity"):
return math.Inf(-1), true
case equalIgnoreCase(s, "+inf"),
equalIgnoreCase(s, "+infinity"),
equalIgnoreCase(s, "inf"),
equalIgnoreCase(s, "infinity"):
return math.Inf(1), true
if len(s) == 0 {
return
}
switch s[0] {
default:
return
case '+':
if equalIgnoreCase(s, "+inf") || equalIgnoreCase(s, "+infinity") {
return math.Inf(1), true
}
case '-':
if equalIgnoreCase(s, "-inf") || equalIgnoreCase(s, "-infinity") {
return math.Inf(-1), true
}
case 'n', 'N':
if equalIgnoreCase(s, "nan") {
return math.NaN(), true
}
case 'i', 'I':
if equalIgnoreCase(s, "inf") || equalIgnoreCase(s, "infinity") {
return math.Inf(1), true
}
}
return
}
@ -142,6 +153,105 @@ func (b *decimal) set(s string) (ok bool) {
return
}
// readFloat reads a decimal mantissa and exponent from a float
// string representation. It sets ok to false if the number could
// not fit return types or is invalid.
func readFloat(s string) (mantissa uint64, exp int, neg, trunc, ok bool) {
const uint64digits = 19
i := 0
// optional sign
if i >= len(s) {
return
}
switch {
case s[i] == '+':
i++
case s[i] == '-':
neg = true
i++
}
// digits
sawdot := false
sawdigits := false
nd := 0
ndMant := 0
dp := 0
for ; i < len(s); i++ {
switch c := s[i]; true {
case c == '.':
if sawdot {
return
}
sawdot = true
dp = nd
continue
case '0' <= c && c <= '9':
sawdigits = true
if c == '0' && nd == 0 { // ignore leading zeros
dp--
continue
}
nd++
if ndMant < uint64digits {
mantissa *= 10
mantissa += uint64(c - '0')
ndMant++
} else if s[i] != '0' {
trunc = true
}
continue
}
break
}
if !sawdigits {
return
}
if !sawdot {
dp = nd
}
// optional exponent moves decimal point.
// if we read a very large, very long number,
// just be sure to move the decimal point by
// a lot (say, 100000). it doesn't matter if it's
// not the exact number.
if i < len(s) && (s[i] == 'e' || s[i] == 'E') {
i++
if i >= len(s) {
return
}
esign := 1
if s[i] == '+' {
i++
} else if s[i] == '-' {
i++
esign = -1
}
if i >= len(s) || s[i] < '0' || s[i] > '9' {
return
}
e := 0
for ; i < len(s) && '0' <= s[i] && s[i] <= '9'; i++ {
if e < 10000 {
e = e*10 + int(s[i]) - '0'
}
}
dp += e * esign
}
if i != len(s) {
return
}
exp = dp - ndMant
ok = true
return
}
// decimal power of ten to binary power of two.
var powtab = []int{1, 3, 6, 9, 13, 16, 19, 23, 26}
@ -243,19 +353,6 @@ out:
return bits, overflow
}
// Compute exact floating-point integer from d's digits.
// Caller is responsible for avoiding overflow.
func (d *decimal) atof64int() float64 {
f := 0.0
for i := 0; i < d.nd; i++ {
f = f*10 + float64(d.d[i]-'0')
}
if d.neg {
f = -f
}
return f
}
func (d *decimal) atof32int() float32 {
f := float32(0)
for i := 0; i < d.nd; i++ {
@ -267,18 +364,6 @@ func (d *decimal) atof32int() float32 {
return f
}
// Reads a uint64 decimal mantissa, which might be truncated.
func (d *decimal) atou64() (mant uint64, digits int) {
const uint64digits = 19
for i, c := range d.d[:d.nd] {
if i == uint64digits {
return mant, i
}
mant = 10*mant + uint64(c-'0')
}
return mant, d.nd
}
// Exact powers of 10.
var float64pow10 = []float64{
1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9,
@ -287,38 +372,41 @@ var float64pow10 = []float64{
}
var float32pow10 = []float32{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10}
// If possible to convert decimal d to 64-bit float f exactly,
// If possible to convert decimal representation to 64-bit float f exactly,
// entirely in floating-point math, do so, avoiding the expense of decimalToFloatBits.
// Three common cases:
// value is exact integer
// value is exact integer * exact power of ten
// value is exact integer / exact power of ten
// These all produce potentially inexact but correctly rounded answers.
func (d *decimal) atof64() (f float64, ok bool) {
// Exact integers are <= 10^15.
// Exact powers of ten are <= 10^22.
if d.nd > 15 {
func atof64exact(mantissa uint64, exp int, neg bool) (f float64, ok bool) {
if mantissa>>float64info.mantbits != 0 {
return
}
f = float64(mantissa)
if neg {
f = -f
}
switch {
case d.dp == d.nd: // int
f := d.atof64int()
case exp == 0:
// an integer.
return f, true
case d.dp > d.nd && d.dp <= 15+22: // int * 10^k
f := d.atof64int()
k := d.dp - d.nd
// Exact integers are <= 10^15.
// Exact powers of ten are <= 10^22.
case exp > 0 && exp <= 15+22: // int * 10^k
// If exponent is big but number of digits is not,
// can move a few zeros into the integer part.
if k > 22 {
f *= float64pow10[k-22]
k = 22
if exp > 22 {
f *= float64pow10[exp-22]
exp = 22
}
return f * float64pow10[k], true
case d.dp < d.nd && d.nd-d.dp <= 22: // int / 10^k
f := d.atof64int()
return f / float64pow10[d.nd-d.dp], true
if f > 1e15 || f < -1e15 {
// the exponent was really too large.
return
}
return f * float64pow10[exp], true
case exp < 0 && exp >= -22: // int / 10^k
return f / float64pow10[-exp], true
}
return
}
@ -383,26 +471,32 @@ func atof64(s string) (f float64, err error) {
return val, nil
}
if optimize {
// Parse mantissa and exponent.
mantissa, exp, neg, trunc, ok := readFloat(s)
if ok {
// Try pure floating-point arithmetic conversion.
if !trunc {
if f, ok := atof64exact(mantissa, exp, neg); ok {
return f, nil
}
}
// Try another fast path.
ext := new(extFloat)
if ok := ext.AssignDecimal(mantissa, exp, neg, trunc); ok {
b, ovf := ext.floatBits()
f = math.Float64frombits(b)
if ovf {
err = rangeError(fnParseFloat, s)
}
return f, err
}
}
}
var d decimal
if !d.set(s) {
return 0, syntaxError(fnParseFloat, s)
}
if optimize {
if f, ok := d.atof64(); ok {
return f, nil
}
// Try another fast path.
ext := new(extFloat)
if ok := ext.AssignDecimal(&d); ok {
b, ovf := ext.floatBits()
f = math.Float64frombits(b)
if ovf {
err = rangeError(fnParseFloat, s)
}
return f, err
}
}
b, ovf := d.floatBits(&float64info)
f = math.Float64frombits(b)
if ovf {

19
src/pkg/strconv/extfloat.go
View File

@ -264,24 +264,21 @@ var uint64pow10 = [...]uint64{
1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19,
}
// AssignDecimal sets f to an approximate value of the decimal d. It
// AssignDecimal sets f to an approximate value mantissa*10^exp. It
// returns true if the value represented by f is guaranteed to be the
// best approximation of d after being rounded to a float64.
func (f *extFloat) AssignDecimal(d *decimal) (ok bool) {
func (f *extFloat) AssignDecimal(mantissa uint64, exp10 int, neg bool, trunc bool) (ok bool) {
const uint64digits = 19
const errorscale = 8
mant10, digits := d.atou64()
exp10 := d.dp - digits
errors := 0 // An upper bound for error, computed in errorscale*ulp.
if digits < d.nd {
if trunc {
// the decimal number was truncated.
errors += errorscale / 2
}
f.mant = mant10
f.mant = mantissa
f.exp = 0
f.neg = d.neg
f.neg = neg
// Multiply by powers of ten.
i := (exp10 - firstPowerOfTen) / stepPowerOfTen
@ -291,9 +288,9 @@ func (f *extFloat) AssignDecimal(d *decimal) (ok bool) {
adjExp := (exp10 - firstPowerOfTen) % stepPowerOfTen
// We multiply by exp%step
if digits+adjExp <= uint64digits {
// We can multiply the mantissa
f.mant *= uint64(float64pow10[adjExp])
if adjExp < uint64digits && mantissa < uint64pow10[uint64digits-adjExp] {
// We can multiply the mantissa exactly.
f.mant *= uint64pow10[adjExp]
f.Normalize()
} else {
f.Normalize()

10
src/pkg/strconv/strconv_test.go
View File

@ -7,11 +7,13 @@ package strconv_test
import (
"runtime"
. "strconv"
"strings"
"testing"
)
var (
globalBuf [64]byte
nextToOne = "1.00000000000000011102230246251565404236316680908203125" + strings.Repeat("0", 10000) + "1"
mallocTest = []struct {
count int
@ -30,6 +32,14 @@ var (
AppendFloat(localBuf[:0], 1.23, 'g', 5, 64)
}},
{0, `AppendFloat(globalBuf[:0], 1.23, 'g', 5, 64)`, func() { AppendFloat(globalBuf[:0], 1.23, 'g', 5, 64) }},
{0, `ParseFloat("123.45", 64)`, func() { ParseFloat("123.45", 64) }},
{0, `ParseFloat("123.456789123456789", 64)`, func() { ParseFloat("123.456789123456789", 64) }},
{0, `ParseFloat("1.000000000000000111022302462515654042363166809082031251", 64)`, func() {
ParseFloat("1.000000000000000111022302462515654042363166809082031251", 64)
}},
{0, `ParseFloat("1.0000000000000001110223024625156540423631668090820312500...001", 64)`, func() {
ParseFloat(nextToOne, 64)
}},
}
)