You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
79 lines
2.2 KiB
79 lines
2.2 KiB
/*
|
|
Copyright 2017 Google Inc.
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "License");
|
|
you may not use this file except in compliance with the License.
|
|
You may obtain a copy of the License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreed to in writing, software
|
|
distributed under the License is distributed on an "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
See the License for the specific language governing permissions and
|
|
limitations under the License.
|
|
*/
|
|
|
|
// 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)
|
|
}
|
|
|