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strconv: put decimal on stack

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This makes decimal a good test
case for the escape analysis.

With escape analysis:

benchmark                 old ns/op    new ns/op    delta
BenchmarkAtof64Decimal         1954          243  -87.56%
BenchmarkAtof64Float           2008          293  -85.41%
BenchmarkAtof64FloatExp       10106         8814  -12.78%
BenchmarkAtof64Big             5113         3486  -31.82%

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/4861042
This commit is contained in:
Russ Cox 2011-08-25 17:54:14 -04:00
parent dd0b8e7975
commit cb51fdc007
5 changed files with 47 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
src/pkg/strconv/atof.go
View File

@ -56,8 +56,9 @@ func special(s string) (f float64, ok bool) {
}
// TODO(rsc): Better truncation handling.
func stringToDecimal(s string) (neg bool, d *decimal, trunc bool, ok bool) {
func (b *decimal) set(s string) (ok bool) {
i := 0
b.neg = false
// optional sign
if i >= len(s) {
@ -67,12 +68,11 @@ func stringToDecimal(s string) (neg bool, d *decimal, trunc bool, ok bool) {
case s[i] == '+':
i++
case s[i] == '-':
neg = true
b.neg = true
i++
}
// digits
b := new(decimal)
sawdot := false
sawdigits := false
for ; i < len(s); i++ {
@ -137,7 +137,6 @@ func stringToDecimal(s string) (neg bool, d *decimal, trunc bool, ok bool) {
return
}
d = b
ok = true
return
}
@ -145,7 +144,7 @@ func stringToDecimal(s string) (neg bool, d *decimal, trunc bool, ok bool) {
// decimal power of ten to binary power of two.
var powtab = []int{1, 3, 6, 9, 13, 16, 19, 23, 26}
func decimalToFloatBits(neg bool, d *decimal, trunc bool, flt *floatInfo) (b uint64, overflow bool) {
func (d *decimal) floatBits(flt *floatInfo) (b uint64, overflow bool) {
var exp int
var mant uint64
@ -209,7 +208,8 @@ func decimalToFloatBits(neg bool, d *decimal, trunc bool, flt *floatInfo) (b uin
}
// Extract 1+flt.mantbits bits.
mant = d.Shift(int(1 + flt.mantbits)).RoundedInteger()
d.Shift(int(1 + flt.mantbits))
mant = d.RoundedInteger()
// Rounding might have added a bit; shift down.
if mant == 2<<flt.mantbits {
@ -236,7 +236,7 @@ out:
// Assemble bits.
bits := mant & (uint64(1)<<flt.mantbits - 1)
bits |= uint64((exp-flt.bias)&(1<<flt.expbits-1)) << flt.mantbits
if neg {
if d.neg {
bits |= 1 << flt.mantbits << flt.expbits
}
return bits, overflow
@ -244,24 +244,24 @@ out:
// Compute exact floating-point integer from d's digits.
// Caller is responsible for avoiding overflow.
func decimalAtof64Int(neg bool, d *decimal) float64 {
func (d *decimal) atof64int() float64 {
f := 0.0
for i := 0; i < d.nd; i++ {
f = f*10 + float64(d.d[i]-'0')
}
if neg {
f *= -1 // BUG work around 6g f = -f.
if d.neg {
f = -f
}
return f
}
func decimalAtof32Int(neg bool, d *decimal) float32 {
func (d *decimal) atof32int() float32 {
f := float32(0)
for i := 0; i < d.nd; i++ {
f = f*10 + float32(d.d[i]-'0')
}
if neg {
f *= -1 // BUG work around 6g f = -f.
if d.neg {
f = -f
}
return f
}
@ -281,7 +281,7 @@ var float32pow10 = []float32{1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1
// 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 decimalAtof64(neg bool, d *decimal, trunc bool) (f float64, ok bool) {
func (d *decimal) atof64() (f float64, ok bool) {
// Exact integers are <= 10^15.
// Exact powers of ten are <= 10^22.
if d.nd > 15 {
@ -289,11 +289,11 @@ func decimalAtof64(neg bool, d *decimal, trunc bool) (f float64, ok bool) {
}
switch {
case d.dp == d.nd: // int
f := decimalAtof64Int(neg, d)
f := d.atof64int()
return f, true
case d.dp > d.nd && d.dp <= 15+22: // int * 10^k
f := decimalAtof64Int(neg, d)
f := d.atof64int()
k := d.dp - d.nd
// If exponent is big but number of digits is not,
// can move a few zeros into the integer part.
@ -304,7 +304,7 @@ func decimalAtof64(neg bool, d *decimal, trunc bool) (f float64, ok bool) {
return f * float64pow10[k], true
case d.dp < d.nd && d.nd-d.dp <= 22: // int / 10^k
f := decimalAtof64Int(neg, d)
f := d.atof64int()
return f / float64pow10[d.nd-d.dp], true
}
return
@ -312,7 +312,7 @@ func decimalAtof64(neg bool, d *decimal, trunc bool) (f float64, ok bool) {
// If possible to convert decimal d to 32-bit float f exactly,
// entirely in floating-point math, do so, avoiding the machinery above.
func decimalAtof32(neg bool, d *decimal, trunc bool) (f float32, ok bool) {
func (d *decimal) atof32() (f float32, ok bool) {
// Exact integers are <= 10^7.
// Exact powers of ten are <= 10^10.
if d.nd > 7 {
@ -320,11 +320,11 @@ func decimalAtof32(neg bool, d *decimal, trunc bool) (f float32, ok bool) {
}
switch {
case d.dp == d.nd: // int
f := decimalAtof32Int(neg, d)
f := d.atof32int()
return f, true
case d.dp > d.nd && d.dp <= 7+10: // int * 10^k
f := decimalAtof32Int(neg, d)
f := d.atof32int()
k := d.dp - d.nd
// If exponent is big but number of digits is not,
// can move a few zeros into the integer part.
@ -335,7 +335,7 @@ func decimalAtof32(neg bool, d *decimal, trunc bool) (f float32, ok bool) {
return f * float32pow10[k], true
case d.dp < d.nd && d.nd-d.dp <= 10: // int / 10^k
f := decimalAtof32Int(neg, d)
f := d.atof32int()
return f / float32pow10[d.nd-d.dp], true
}
return
@ -360,16 +360,16 @@ func Atof32(s string) (f float32, err os.Error) {
return float32(val), nil
}
neg, d, trunc, ok := stringToDecimal(s)
if !ok {
var d decimal
if !d.set(s) {
return 0, &NumError{s, os.EINVAL}
}
if optimize {
if f, ok := decimalAtof32(neg, d, trunc); ok {
if f, ok := d.atof32(); ok {
return f, nil
}
}
b, ovf := decimalToFloatBits(neg, d, trunc, &float32info)
b, ovf := d.floatBits(&float32info)
f = math.Float32frombits(uint32(b))
if ovf {
err = &NumError{s, os.ERANGE}
@ -385,16 +385,16 @@ func Atof64(s string) (f float64, err os.Error) {
return val, nil
}
neg, d, trunc, ok := stringToDecimal(s)
if !ok {
var d decimal
if !d.set(s) {
return 0, &NumError{s, os.EINVAL}
}
if optimize {
if f, ok := decimalAtof64(neg, d, trunc); ok {
if f, ok := d.atof64(); ok {
return f, nil
}
}
b, ovf := decimalToFloatBits(neg, d, trunc, &float64info)
b, ovf := d.floatBits(&float64info)
f = math.Float64frombits(b)
if ovf {
err = &NumError{s, os.ERANGE}

1
src/pkg/strconv/atof_test.go
View File

@ -34,6 +34,7 @@ var atoftests = []atofTest{
{"100000000000000016777215", "1.0000000000000001e+23", nil},
{"100000000000000016777216", "1.0000000000000003e+23", nil},
{"-1", "-1", nil},
{"-0.1", "-0.1", nil},
{"-0", "-0", nil},
{"1e-20", "1e-20", nil},
{"625e-3", "0.625", nil},

11
src/pkg/strconv/decimal.go
View File

@ -14,9 +14,10 @@ package strconv
type decimal struct {
// TODO(rsc): Can make d[] a bit smaller and add
// truncated bool;
d [2000]byte // digits
nd int // number of digits used
dp int // decimal point
d [2000]byte // digits
nd int // number of digits used
dp int // decimal point
neg bool
}
func (a *decimal) String() string {
@ -266,8 +267,7 @@ func leftShift(a *decimal, k uint) {
}
// Binary shift left (k > 0) or right (k < 0).
// Returns receiver for convenience.
func (a *decimal) Shift(k int) *decimal {
func (a *decimal) Shift(k int) {
switch {
case a.nd == 0:
// nothing to do: a == 0
@ -284,7 +284,6 @@ func (a *decimal) Shift(k int) *decimal {
}
rightShift(a, uint(-k))
}
return a
}
// If we chop a at nd digits, should we round up?

8
src/pkg/strconv/decimal_test.go
View File

@ -32,7 +32,9 @@ var shifttests = []shiftTest{
func TestDecimalShift(t *testing.T) {
for i := 0; i < len(shifttests); i++ {
test := &shifttests[i]
s := NewDecimal(test.i).Shift(test.shift).String()
d := NewDecimal(test.i)
d.Shift(test.shift)
s := d.String()
if s != test.out {
t.Errorf("Decimal %v << %v = %v, want %v",
test.i, test.shift, s, test.out)
@ -108,7 +110,9 @@ var roundinttests = []roundIntTest{
func TestDecimalRoundedInteger(t *testing.T) {
for i := 0; i < len(roundinttests); i++ {
test := roundinttests[i]
int := NewDecimal(test.i).Shift(test.shift).RoundedInteger()
d := NewDecimal(test.i)
d.Shift(test.shift)
int := d.RoundedInteger()
if int != test.int {
t.Errorf("Decimal %v >> %v RoundedInteger = %v, want %v",
test.i, test.shift, int, test.int)

9
src/pkg/strconv/ftoa.go
View File

@ -98,7 +98,8 @@ func genericFtoa(bits uint64, fmt byte, prec int, flt *floatInfo) string {
// The shift is exp - flt.mantbits because mant is a 1-bit integer
// followed by a flt.mantbits fraction, and we are treating it as
// a 1+flt.mantbits-bit integer.
d := newDecimal(mant).Shift(exp - int(flt.mantbits))
d := newDecimal(mant)
d.Shift(exp - int(flt.mantbits))
// Round appropriately.
// Negative precision means "only as much as needed to be exact."
@ -183,7 +184,8 @@ func roundShortest(d *decimal, mant uint64, exp int, flt *floatInfo) {
// d = mant << (exp - mantbits)
// Next highest floating point number is mant+1 << exp-mantbits.
// Our upper bound is halfway inbetween, mant*2+1 << exp-mantbits-1.
upper := newDecimal(mant*2 + 1).Shift(exp - int(flt.mantbits) - 1)
upper := newDecimal(mant*2 + 1)
upper.Shift(exp - int(flt.mantbits) - 1)
// d = mant << (exp - mantbits)
// Next lowest floating point number is mant-1 << exp-mantbits,
@ -201,7 +203,8 @@ func roundShortest(d *decimal, mant uint64, exp int, flt *floatInfo) {
mantlo = mant*2 - 1
explo = exp - 1
}
lower := newDecimal(mantlo*2 + 1).Shift(explo - int(flt.mantbits) - 1)
lower := newDecimal(mantlo*2 + 1)
lower.Shift(explo - int(flt.mantbits) - 1)
// The upper and lower bounds are possible outputs only if
// the original mantissa is even, so that IEEE round-to-even