github.com/bingoohuang/gg@v0.0.0-20240325092523-45da7dee9335/pkg/sqlparse/hack/hack.go (about)

     1  /*
     2  Copyright 2017 Google Inc.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  // Package hack gives you some efficient functionality at the cost of
    18  // breaking some Go rules.
    19  package hack
    20  
    21  import (
    22  	"reflect"
    23  	"unsafe"
    24  )
    25  
    26  // StringArena lets you consolidate allocations for a group of strings
    27  // that have similar life length
    28  type StringArena struct {
    29  	buf []byte
    30  	str string
    31  }
    32  
    33  // NewStringArena creates an arena of the specified size.
    34  func NewStringArena(size int) *StringArena {
    35  	sa := &StringArena{buf: make([]byte, 0, size)}
    36  	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&sa.buf))
    37  	pstring := (*reflect.StringHeader)(unsafe.Pointer(&sa.str))
    38  	pstring.Data = pbytes.Data
    39  	pstring.Len = pbytes.Cap
    40  	return sa
    41  }
    42  
    43  // NewString copies a byte slice into the arena and returns it as a string.
    44  // If the arena is full, it returns a traditional go string.
    45  func (sa *StringArena) NewString(b []byte) string {
    46  	if len(b) == 0 {
    47  		return ""
    48  	}
    49  	if len(sa.buf)+len(b) > cap(sa.buf) {
    50  		return string(b)
    51  	}
    52  	start := len(sa.buf)
    53  	sa.buf = append(sa.buf, b...)
    54  	return sa.str[start : start+len(b)]
    55  }
    56  
    57  // SpaceLeft returns the amount of space left in the arena.
    58  func (sa *StringArena) SpaceLeft() int {
    59  	return cap(sa.buf) - len(sa.buf)
    60  }
    61  
    62  // String force casts a []byte to a string.
    63  // USE AT YOUR OWN RISK
    64  func String(b []byte) (s string) {
    65  	if len(b) == 0 {
    66  		return ""
    67  	}
    68  	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
    69  	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
    70  	pstring.Data = pbytes.Data
    71  	pstring.Len = pbytes.Len
    72  	return
    73  }
    74  
    75  // StringPointer returns &s[0], which is not allowed in go
    76  func StringPointer(s string) unsafe.Pointer {
    77  	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
    78  	return unsafe.Pointer(pstring.Data)
    79  }