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.
172 lines
4.0 KiB
172 lines
4.0 KiB
// Copyright 2014-2021 Ulrich Kunitz. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package lzma
|
|
|
|
import (
|
|
"errors"
|
|
)
|
|
|
|
// buffer provides a circular buffer of bytes. If the front index equals
|
|
// the rear index the buffer is empty. As a consequence front cannot be
|
|
// equal rear for a full buffer. So a full buffer has a length that is
|
|
// one byte less the the length of the data slice.
|
|
type buffer struct {
|
|
data []byte
|
|
front int
|
|
rear int
|
|
}
|
|
|
|
// newBuffer creates a buffer with the given size.
|
|
func newBuffer(size int) *buffer {
|
|
return &buffer{data: make([]byte, size+1)}
|
|
}
|
|
|
|
// Cap returns the capacity of the buffer.
|
|
func (b *buffer) Cap() int {
|
|
return len(b.data) - 1
|
|
}
|
|
|
|
// Resets the buffer. The front and rear index are set to zero.
|
|
func (b *buffer) Reset() {
|
|
b.front = 0
|
|
b.rear = 0
|
|
}
|
|
|
|
// Buffered returns the number of bytes buffered.
|
|
func (b *buffer) Buffered() int {
|
|
delta := b.front - b.rear
|
|
if delta < 0 {
|
|
delta += len(b.data)
|
|
}
|
|
return delta
|
|
}
|
|
|
|
// Available returns the number of bytes available for writing.
|
|
func (b *buffer) Available() int {
|
|
delta := b.rear - 1 - b.front
|
|
if delta < 0 {
|
|
delta += len(b.data)
|
|
}
|
|
return delta
|
|
}
|
|
|
|
// addIndex adds a non-negative integer to the index i and returns the
|
|
// resulting index. The function takes care of wrapping the index as
|
|
// well as potential overflow situations.
|
|
func (b *buffer) addIndex(i int, n int) int {
|
|
// subtraction of len(b.data) prevents overflow
|
|
i += n - len(b.data)
|
|
if i < 0 {
|
|
i += len(b.data)
|
|
}
|
|
return i
|
|
}
|
|
|
|
// Read reads bytes from the buffer into p and returns the number of
|
|
// bytes read. The function never returns an error but might return less
|
|
// data than requested.
|
|
func (b *buffer) Read(p []byte) (n int, err error) {
|
|
n, err = b.Peek(p)
|
|
b.rear = b.addIndex(b.rear, n)
|
|
return n, err
|
|
}
|
|
|
|
// Peek reads bytes from the buffer into p without changing the buffer.
|
|
// Peek will never return an error but might return less data than
|
|
// requested.
|
|
func (b *buffer) Peek(p []byte) (n int, err error) {
|
|
m := b.Buffered()
|
|
n = len(p)
|
|
if m < n {
|
|
n = m
|
|
p = p[:n]
|
|
}
|
|
k := copy(p, b.data[b.rear:])
|
|
if k < n {
|
|
copy(p[k:], b.data)
|
|
}
|
|
return n, nil
|
|
}
|
|
|
|
// Discard skips the n next bytes to read from the buffer, returning the
|
|
// bytes discarded.
|
|
//
|
|
// If Discards skips fewer than n bytes, it returns an error.
|
|
func (b *buffer) Discard(n int) (discarded int, err error) {
|
|
if n < 0 {
|
|
return 0, errors.New("buffer.Discard: negative argument")
|
|
}
|
|
m := b.Buffered()
|
|
if m < n {
|
|
n = m
|
|
err = errors.New(
|
|
"buffer.Discard: discarded less bytes then requested")
|
|
}
|
|
b.rear = b.addIndex(b.rear, n)
|
|
return n, err
|
|
}
|
|
|
|
// ErrNoSpace indicates that there is insufficient space for the Write
|
|
// operation.
|
|
var ErrNoSpace = errors.New("insufficient space")
|
|
|
|
// Write puts data into the buffer. If less bytes are written than
|
|
// requested ErrNoSpace is returned.
|
|
func (b *buffer) Write(p []byte) (n int, err error) {
|
|
m := b.Available()
|
|
n = len(p)
|
|
if m < n {
|
|
n = m
|
|
p = p[:m]
|
|
err = ErrNoSpace
|
|
}
|
|
k := copy(b.data[b.front:], p)
|
|
if k < n {
|
|
copy(b.data, p[k:])
|
|
}
|
|
b.front = b.addIndex(b.front, n)
|
|
return n, err
|
|
}
|
|
|
|
// WriteByte writes a single byte into the buffer. The error ErrNoSpace
|
|
// is returned if no single byte is available in the buffer for writing.
|
|
func (b *buffer) WriteByte(c byte) error {
|
|
if b.Available() < 1 {
|
|
return ErrNoSpace
|
|
}
|
|
b.data[b.front] = c
|
|
b.front = b.addIndex(b.front, 1)
|
|
return nil
|
|
}
|
|
|
|
// prefixLen returns the length of the common prefix of a and b.
|
|
func prefixLen(a, b []byte) int {
|
|
if len(a) > len(b) {
|
|
a, b = b, a
|
|
}
|
|
for i, c := range a {
|
|
if b[i] != c {
|
|
return i
|
|
}
|
|
}
|
|
return len(a)
|
|
}
|
|
|
|
// matchLen returns the length of the common prefix for the given
|
|
// distance from the rear and the byte slice p.
|
|
func (b *buffer) matchLen(distance int, p []byte) int {
|
|
var n int
|
|
i := b.rear - distance
|
|
if i < 0 {
|
|
if n = prefixLen(p, b.data[len(b.data)+i:]); n < -i {
|
|
return n
|
|
}
|
|
p = p[n:]
|
|
i = 0
|
|
}
|
|
n += prefixLen(p, b.data[i:])
|
|
return n
|
|
}
|