strconv: put decimal on stack

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

diff --git a/src/pkg/strconv/atof.go b/src/pkg/strconv/atof.go
index 38b38053ce033d2c44851679014c7784e98656cb..86c56f7fd7e45f8f56f38f1ec2c4c7650f18aea4 100644 (file)
--- a/src/pkg/strconv/atof.go
+++ b/src/pkg/strconv/atof.go
@@ -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}

diff --git a/src/pkg/strconv/atof_test.go b/src/pkg/strconv/atof_test.go
index 0fdd0ea982baa1257bf20722b9c0b52fb34f3bad..23aafc1e5d7b025cda63cd70ac6a81369030e192 100644 (file)
--- a/src/pkg/strconv/atof_test.go
+++ b/src/pkg/strconv/atof_test.go
@@ -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},

diff --git a/src/pkg/strconv/decimal.go b/src/pkg/strconv/decimal.go
index 783065bfbf23ba43e7a6f5407da6737b360e8e6d..f572ea4a22d5056e07ad0b22cd867180f9866a78 100644 (file)
--- a/src/pkg/strconv/decimal.go
+++ b/src/pkg/strconv/decimal.go
@@ -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?

diff --git a/src/pkg/strconv/decimal_test.go b/src/pkg/strconv/decimal_test.go
index 9b790351673069e5185451b546cad120c0aa1c01..deb2e02f6108478e9f64270faf0abdb775d24222 100644 (file)
--- a/src/pkg/strconv/decimal_test.go
+++ b/src/pkg/strconv/decimal_test.go
@@ -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)

diff --git a/src/pkg/strconv/ftoa.go b/src/pkg/strconv/ftoa.go
index b6049c545899330847d96c02f15be8b456cb3124..07fe806b97dec2cdf3ea724a5ef594ec26f7546c 100644 (file)
--- a/src/pkg/strconv/ftoa.go
+++ b/src/pkg/strconv/ftoa.go
@@ -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