Permalink
Browse files

strconv: optimize formatting for small decimal ints

Avoid memory allocations by returning pre-calculated strings
for decimal ints in the range 0..99.

Benchmark results:

name              old time/op    new time/op    delta
FormatInt-4         2.45µs ± 1%    2.40µs ± 1%    -1.86%  (p=0.000 n=8+9)
AppendInt-4         1.67µs ± 1%    1.65µs ± 0%    -0.92%  (p=0.000 n=10+10)
FormatUint-4         676ns ± 3%     669ns ± 1%      ~     (p=0.146 n=10+10)
AppendUint-4         467ns ± 2%     474ns ± 0%    +1.58%  (p=0.000 n=10+10)
FormatIntSmall-4    29.6ns ± 2%     3.3ns ± 0%   -88.98%  (p=0.000 n=10+9)
AppendIntSmall-4    16.0ns ± 1%     8.5ns ± 0%   -46.98%  (p=0.000 n=10+9)

name              old alloc/op   new alloc/op   delta
FormatInt-4           576B ± 0%      576B ± 0%      ~     (all equal)
AppendInt-4          0.00B          0.00B           ~     (all equal)
FormatUint-4          224B ± 0%      224B ± 0%      ~     (all equal)
AppendUint-4         0.00B          0.00B           ~     (all equal)
FormatIntSmall-4     2.00B ± 0%     0.00B       -100.00%  (p=0.000 n=10+10)
AppendIntSmall-4     0.00B          0.00B           ~     (all equal)

name              old allocs/op  new allocs/op  delta
FormatInt-4           37.0 ± 0%      35.0 ± 0%    -5.41%  (p=0.000 n=10+10)
AppendInt-4           0.00           0.00           ~     (all equal)
FormatUint-4          6.00 ± 0%      6.00 ± 0%      ~     (all equal)
AppendUint-4          0.00           0.00           ~     (all equal)
FormatIntSmall-4      1.00 ± 0%      0.00       -100.00%  (p=0.000 n=10+10)
AppendIntSmall-4      0.00           0.00           ~     (all equal)

Fixes #19445

Change-Id: Ib1f8922f2e0b13743c847ee9e703d1dab77f705c
Reviewed-on: https://go-review.googlesource.com/37963
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
  • Loading branch information...
valyala authored and griesemer committed Mar 9, 2017
1 parent dd9892e commit bc8b9b23ca3f33e738d85c4734bd35dfe63e9ac4
Showing with 52 additions and 4 deletions.
  1. +25 −0 src/strconv/itoa.go
  2. +27 −4 src/strconv/itoa_test.go
View
@@ -8,6 +8,9 @@ package strconv
// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
// for digit values >= 10.
func FormatUint(i uint64, base int) string {
if i < uint64(len(smallints)) && base == 10 {
return smallints[i]
}
_, s := formatBits(nil, i, base, false, false)
return s
}
@@ -16,6 +19,9 @@ func FormatUint(i uint64, base int) string {
// for 2 <= base <= 36. The result uses the lower-case letters 'a' to 'z'
// for digit values >= 10.
func FormatInt(i int64, base int) string {
if 0 <= i && i < int64(len(smallints)) && base == 10 {
return smallints[i]
}
_, s := formatBits(nil, uint64(i), base, i < 0, false)
return s
}
@@ -28,13 +34,19 @@ func Itoa(i int) string {
// AppendInt appends the string form of the integer i,
// as generated by FormatInt, to dst and returns the extended buffer.
func AppendInt(dst []byte, i int64, base int) []byte {
if 0 <= i && i < int64(len(smallints)) && base == 10 {
return append(dst, smallints[i]...)
}
dst, _ = formatBits(dst, uint64(i), base, i < 0, true)
return dst
}
// AppendUint appends the string form of the unsigned integer i,
// as generated by FormatUint, to dst and returns the extended buffer.
func AppendUint(dst []byte, i uint64, base int) []byte {
if i < uint64(len(smallints)) && base == 10 {
return append(dst, smallints[i]...)
}
dst, _ = formatBits(dst, i, base, false, true)
return dst
}
@@ -43,6 +55,19 @@ const host32bit = ^uint(0)>>32 == 0
const digits = "0123456789abcdefghijklmnopqrstuvwxyz"
var smallints = [...]string{
"0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
"10", "11", "12", "13", "14", "15", "16", "17", "18", "19",
"20", "21", "22", "23", "24", "25", "26", "27", "28", "29",
"30", "31", "32", "33", "34", "35", "36", "37", "38", "39",
"40", "41", "42", "43", "44", "45", "46", "47", "48", "49",
"50", "51", "52", "53", "54", "55", "56", "57", "58", "59",
"60", "61", "62", "63", "64", "65", "66", "67", "68", "69",
"70", "71", "72", "73", "74", "75", "76", "77", "78", "79",
"80", "81", "82", "83", "84", "85", "86", "87", "88", "89",
"90", "91", "92", "93", "94", "95", "96", "97", "98", "99",
}
var shifts = [len(digits) + 1]uint{
1 << 1: 1,
1 << 2: 2,
View
@@ -129,7 +129,8 @@ func TestUitoa(t *testing.T) {
func BenchmarkFormatInt(b *testing.B) {
for i := 0; i < b.N; i++ {
for _, test := range itob64tests {
FormatInt(test.in, test.base)
s := FormatInt(test.in, test.base)
BenchSink += len(s)
}
}
}
@@ -138,15 +139,17 @@ func BenchmarkAppendInt(b *testing.B) {
dst := make([]byte, 0, 30)
for i := 0; i < b.N; i++ {
for _, test := range itob64tests {
AppendInt(dst, test.in, test.base)
dst = AppendInt(dst[:0], test.in, test.base)
BenchSink += len(dst)
}
}
}
func BenchmarkFormatUint(b *testing.B) {
for i := 0; i < b.N; i++ {
for _, test := range uitob64tests {
FormatUint(test.in, test.base)
s := FormatUint(test.in, test.base)
BenchSink += len(s)
}
}
}
@@ -155,7 +158,27 @@ func BenchmarkAppendUint(b *testing.B) {
dst := make([]byte, 0, 30)
for i := 0; i < b.N; i++ {
for _, test := range uitob64tests {
AppendUint(dst, test.in, test.base)
dst = AppendUint(dst[:0], test.in, test.base)
BenchSink += len(dst)
}
}
}
func BenchmarkFormatIntSmall(b *testing.B) {
const smallInt = 42
for i := 0; i < b.N; i++ {
s := FormatInt(smallInt, 10)
BenchSink += len(s)
}
}
func BenchmarkAppendIntSmall(b *testing.B) {
dst := make([]byte, 0, 30)
const smallInt = 42
for i := 0; i < b.N; i++ {
dst = AppendInt(dst[:0], smallInt, 10)
BenchSink += len(dst)
}
}
var BenchSink int // make sure compiler cannot optimize away benchmarks

0 comments on commit bc8b9b2

Please sign in to comment.