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encoding/xml: simplify slice-growing logic in rawToken

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It appears that old code (from 2009) in xml.(*Decoder).rawToken
replicates append's slice-growing functionality by allocating a new,
bigger backing array and then calling copy.

Simplifying the code by replacing it with a single append call does
not seem to hurt performance:

name         old time/op    new time/op    delta
Marshal-4      11.2µs ± 1%    11.3µs ±10%    ~     (p=0.069 n=19+17)
Unmarshal-4    28.6µs ± 1%    28.4µs ± 1%  -0.60%  (p=0.000 n=20+18)

name         old alloc/op   new alloc/op   delta
Marshal-4      5.78kB ± 0%    5.78kB ± 0%    ~     (all equal)
Unmarshal-4    8.61kB ± 0%    8.27kB ± 0%  -3.90%  (p=0.000 n=20+20)

name         old allocs/op  new allocs/op  delta
Marshal-4        23.0 ± 0%      23.0 ± 0%    ~     (all equal)
Unmarshal-4       189 ± 0%       190 ± 0%  +0.53%  (p=0.000 n=20+20)

Change-Id: Ie580d1216a44760e611e63dee2c339af5465aea5
Reviewed-on: https://go-review.googlesource.com/86655
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Alberto Donizetti 2018-01-08 13:03:57 +01:00 committed by Brad Fitzpatrick
parent bb355ed5eb
commit 252ee90971
1 changed files with 2 additions and 12 deletions
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14
src/encoding/xml/xml.go
View File

@ -806,18 +806,7 @@ func (d *Decoder) rawToken() (Token, error) {
}
d.ungetc(b)
n := len(attr)
if n >= cap(attr) {
nCap := 2 * cap(attr)
if nCap == 0 {
nCap = 4
}
nattr := make([]Attr, n, nCap)
copy(nattr, attr)
attr = nattr
}
attr = attr[0 : n+1]
a := &attr[n]
a := Attr{}
if a.Name, ok = d.nsname(); !ok {
if d.err == nil {
d.err = d.syntaxError("expected attribute name in element")
@ -843,6 +832,7 @@ func (d *Decoder) rawToken() (Token, error) {
}
a.Value = string(data)
}
attr = append(attr, a)
}
if empty {
d.needClose = true