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encoding/json: reduce allocations by Decoder for \uXXXX

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Manually convert hex escape sequence to rune instead of calling
strconv.ParseUint.

This inlines the unhex func from docs (and many other packages).

name              old time/op    new time/op    delta
UnicodeDecoder-4     468ns ± 1%     402ns ± 1%  -14.26%  (p=0.000
n=10+10)

name              old speed      new speed      delta
UnicodeDecoder-4  29.9MB/s ± 1%  34.8MB/s ± 1%  +16.59%  (p=0.000
n=10+10)

name              old alloc/op   new alloc/op   delta
UnicodeDecoder-4     44.0B ± 0%     36.0B ± 0%  -18.18%  (p=0.000
n=10+10)

name              old allocs/op  new allocs/op  delta
UnicodeDecoder-4      4.00 ± 0%      2.00 ± 0%  -50.00%  (p=0.000
n=10+10)

Fixes #20567

Change-Id: If350978d5bb98ff517485752184d02249f5d1f3a
Reviewed-on: https://go-review.googlesource.com/44738
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Michael Schurter 2017-06-03 13:36:54 -07:00 • committed by Brad Fitzpatrick
parent 71aee2a190
commit 7eb7f8f5a7
2 changed files with 29 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

18
src/encoding/json/decode.go
View file

@ -1148,11 +1148,21 @@ func getu4(s []byte) rune {
if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
return -1
}
r, err := strconv.ParseUint(string(s[2:6]), 16, 64)
if err != nil {
return -1
var r rune
for _, c := range s[2:6] {
switch {
case '0' <= c && c <= '9':
c = c - '0'
case 'a' <= c && c <= 'f':
c = c - 'a' + 10
case 'A' <= c && c <= 'F':
c = c - 'A' + 10
default:
return -1
}
r = r*16 + rune(c)
}
return rune(r)
return r
}
// unquote converts a quoted JSON string literal s into an actual string t.