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types/wgkey: optimize Key.ShortString

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name           old time/op    new time/op    delta
ShortString-8    82.6ns ± 0%    15.6ns ± 0%  -81.07%  (p=0.008 n=5+5)

name           old alloc/op   new alloc/op   delta
ShortString-8      104B ± 0%        8B ± 0%  -92.31%  (p=0.008 n=5+5)

name           old allocs/op  new allocs/op  delta
ShortString-8      3.00 ± 0%      1.00 ± 0%  -66.67%  (p=0.008 n=5+5)

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>
This commit is contained in:
Josh Bleecher Snyder 2021-05-07 21:38:31 -07:00 committed by Josh Bleecher Snyder
parent 7cd4766d5e
commit e9066ee625
1 changed files with 10 additions and 2 deletions
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12
types/wgkey/key.go
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@ -78,8 +78,16 @@ func (k Key) HexString() string { return hex.EncodeToString(k[:]) }
func (k Key) Equal(k2 Key) bool { return subtle.ConstantTimeCompare(k[:], k2[:]) == 1 }
func (k *Key) ShortString() string {
long := k.Base64()
return "[" + long[0:5] + "]"
// The goal here is to generate "[" + base64.StdEncoding.EncodeToString(k[:])[:5] + "]".
// Since we only care about the first 5 characters, it suffices to encode the first 4 bytes of k.
// Encoding those 4 bytes requires 8 bytes.
// Make dst have size 9, to fit the leading '[' plus those 8 bytes.
// We slice the unused ones away at the end.
dst := make([]byte, 9)
dst[0] = '['
base64.StdEncoding.Encode(dst[1:], k[:4])
dst[6] = ']'
return string(dst[:7])
}
func (k *Key) IsZero() bool {