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// Copyright 2021 Google LLC
//
// 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 runes provides interfaces and utilities for working with runes.
package runes
import (
"strings"
"unicode/utf8"
)
// Buffer is an interface for accessing a contiguous array of code points.
type Buffer interface {
Get(i int) rune
Slice(i, j int) string
Len() int
}
type emptyBuffer struct{}
func (e *emptyBuffer) Get(i int) rune {
panic("slice index out of bounds")
}
func (e *emptyBuffer) Slice(i, j int) string {
if i != 0 || i != j {
panic("slice index out of bounds")
}
return ""
}
func (e *emptyBuffer) Len() int {
return 0
}
var _ Buffer = &emptyBuffer{}
// asciiBuffer is an implementation for an array of code points that contain code points only from
// the ASCII character set.
type asciiBuffer struct {
arr []byte
}
func (a *asciiBuffer) Get(i int) rune {
return rune(uint32(a.arr[i]))
}
func (a *asciiBuffer) Slice(i, j int) string {
return string(a.arr[i:j])
}
func (a *asciiBuffer) Len() int {
return len(a.arr)
}
var _ Buffer = &asciiBuffer{}
// basicBuffer is an implementation for an array of code points that contain code points from both
// the Latin-1 character set and Basic Multilingual Plane.
type basicBuffer struct {
arr []uint16
}
func (b *basicBuffer) Get(i int) rune {
return rune(uint32(b.arr[i]))
}
func (b *basicBuffer) Slice(i, j int) string {
var str strings.Builder
str.Grow((j - i) * 3) // Worst case encoding size for 0xffff is 3.
for ; i < j; i++ {
str.WriteRune(rune(uint32(b.arr[i])))
}
return str.String()
}
func (b *basicBuffer) Len() int {
return len(b.arr)
}
var _ Buffer = &basicBuffer{}
// supplementalBuffer is an implementation for an array of code points that contain code points from
// the Latin-1 character set, Basic Multilingual Plane, or the Supplemental Multilingual Plane.
type supplementalBuffer struct {
arr []rune
}
func (s *supplementalBuffer) Get(i int) rune {
return rune(uint32(s.arr[i]))
}
func (s *supplementalBuffer) Slice(i, j int) string {
return string(s.arr[i:j])
}
func (s *supplementalBuffer) Len() int {
return len(s.arr)
}
var _ Buffer = &supplementalBuffer{}
var nilBuffer = &emptyBuffer{}
// NewBuffer returns an efficient implementation of Buffer for the given text based on the ranges of
// the encoded code points contained within.
//
// Code points are represented as an array of byte, uint16, or rune. This approach ensures that
// each index represents a code point by itself without needing to use an array of rune. At first
// we assume all code points are less than or equal to '\u007f'. If this holds true, the
// underlying storage is a byte array containing only ASCII characters. If we encountered a code
// point above this range but less than or equal to '\uffff' we allocate a uint16 array, copy the
// elements of previous byte array to the uint16 array, and continue. If this holds true, the
// underlying storage is a uint16 array containing only Unicode characters in the Basic Multilingual
// Plane. If we encounter a code point above '\uffff' we allocate an rune array, copy the previous
// elements of the byte or uint16 array, and continue. The underlying storage is an rune array
// containing any Unicode character.
func NewBuffer(data string) Buffer {
buf, _ := newBuffer(data, false)
return buf
}
// NewBuffer returns an efficient implementation of Buffer for the given text based on the ranges of
// the encoded code points contained within, as well as returning the line offsets.
//
// Code points are represented as an array of byte, uint16, or rune. This approach ensures that
// each index represents a code point by itself without needing to use an array of rune. At first
// we assume all code points are less than or equal to '\u007f'. If this holds true, the
// underlying storage is a byte array containing only ASCII characters. If we encountered a code
// point above this range but less than or equal to '\uffff' we allocate a uint16 array, copy the
// elements of previous byte array to the uint16 array, and continue. If this holds true, the
// underlying storage is a uint16 array containing only Unicode characters in the Basic Multilingual
// Plane. If we encounter a code point above '\uffff' we allocate an rune array, copy the previous
// elements of the byte or uint16 array, and continue. The underlying storage is an rune array
// containing any Unicode character.
func NewBufferAndLineOffsets(data string) (Buffer, []int32) {
return newBuffer(data, true)
}
func newBuffer(data string, lines bool) (Buffer, []int32) {
if len(data) == 0 {
return nilBuffer, []int32{0}
}
var (
idx = 0
off int32 = 0
buf8 = make([]byte, 0, len(data))
buf16 []uint16
buf32 []rune
offs []int32
)
for idx < len(data) {
r, s := utf8.DecodeRuneInString(data[idx:])
idx += s
if lines && r == '\n' {
offs = append(offs, off+1)
}
if r < utf8.RuneSelf {
buf8 = append(buf8, byte(r))
off++
continue
}
if r <= 0xffff {
buf16 = make([]uint16, len(buf8), len(data))
for i, v := range buf8 {
buf16[i] = uint16(v)
}
buf8 = nil
buf16 = append(buf16, uint16(r))
off++
goto copy16
}
buf32 = make([]rune, len(buf8), len(data))
for i, v := range buf8 {
buf32[i] = rune(uint32(v))
}
buf8 = nil
buf32 = append(buf32, r)
off++
goto copy32
}
if lines {
offs = append(offs, off+1)
}
return &asciiBuffer{
arr: buf8,
}, offs
copy16:
for idx < len(data) {
r, s := utf8.DecodeRuneInString(data[idx:])
idx += s
if lines && r == '\n' {
offs = append(offs, off+1)
}
if r <= 0xffff {
buf16 = append(buf16, uint16(r))
off++
continue
}
buf32 = make([]rune, len(buf16), len(data))
for i, v := range buf16 {
buf32[i] = rune(uint32(v))
}
buf16 = nil
buf32 = append(buf32, r)
off++
goto copy32
}
if lines {
offs = append(offs, off+1)
}
return &basicBuffer{
arr: buf16,
}, offs
copy32:
for idx < len(data) {
r, s := utf8.DecodeRuneInString(data[idx:])
idx += s
if lines && r == '\n' {
offs = append(offs, off+1)
}
buf32 = append(buf32, r)
off++
}
if lines {
offs = append(offs, off+1)
}
return &supplementalBuffer{
arr: buf32,
}, offs
}
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