forked from vitessio/vitess
-
Notifications
You must be signed in to change notification settings - Fork 0
/
hack.go
67 lines (59 loc) · 1.78 KB
/
hack.go
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
// Copyright 2012, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package hack gives you some efficient functionality at the cost of
// breaking some Go rules.
package hack
import (
"reflect"
"unsafe"
)
// StringArena lets you consolidate allocations for a group of strings
// that have similar life length
type StringArena struct {
buf []byte
str string
}
// NewStringArena creates an arena of the specified size.
func NewStringArena(size int) *StringArena {
sa := &StringArena{buf: make([]byte, 0, size)}
pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&sa.buf))
pstring := (*reflect.StringHeader)(unsafe.Pointer(&sa.str))
pstring.Data = pbytes.Data
pstring.Len = pbytes.Cap
return sa
}
// NewString copies a byte slice into the arena and returns it as a string.
// If the arena is full, it returns a traditional go string.
func (sa *StringArena) NewString(b []byte) string {
if len(b) == 0 {
return ""
}
if len(sa.buf)+len(b) > cap(sa.buf) {
return string(b)
}
start := len(sa.buf)
sa.buf = append(sa.buf, b...)
return sa.str[start : start+len(b)]
}
// SpaceLeft returns the amount of space left in the arena.
func (sa *StringArena) SpaceLeft() int {
return cap(sa.buf) - len(sa.buf)
}
// String force casts a []byte to a string.
// USE AT YOUR OWN RISK
func String(b []byte) (s string) {
if len(b) == 0 {
return ""
}
pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
pstring.Data = pbytes.Data
pstring.Len = pbytes.Len
return
}
// StringPointer returns &s[0], which is not allowed in go
func StringPointer(s string) unsafe.Pointer {
pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
return unsafe.Pointer(pstring.Data)
}