1// Copyright 2018 Klaus Post. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.
5
6package fse
7
8// byteReader provides a byte reader that reads
9// little endian values from a byte stream.
10// The input stream is manually advanced.
11// The reader performs no bounds checks.
12type byteReader struct {
13	b   []byte
14	off int
15}
16
17// init will initialize the reader and set the input.
18func (b *byteReader) init(in []byte) {
19	b.b = in
20	b.off = 0
21}
22
23// advance the stream b n bytes.
24func (b *byteReader) advance(n uint) {
25	b.off += int(n)
26}
27
28// Int32 returns a little endian int32 starting at current offset.
29func (b byteReader) Int32() int32 {
30	b2 := b.b[b.off : b.off+4 : b.off+4]
31	v3 := int32(b2[3])
32	v2 := int32(b2[2])
33	v1 := int32(b2[1])
34	v0 := int32(b2[0])
35	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
36}
37
38// Uint32 returns a little endian uint32 starting at current offset.
39func (b byteReader) Uint32() uint32 {
40	b2 := b.b[b.off : b.off+4 : b.off+4]
41	v3 := uint32(b2[3])
42	v2 := uint32(b2[2])
43	v1 := uint32(b2[1])
44	v0 := uint32(b2[0])
45	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
46}
47
48// unread returns the unread portion of the input.
49func (b byteReader) unread() []byte {
50	return b.b[b.off:]
51}
52
53// remain will return the number of bytes remaining.
54func (b byteReader) remain() int {
55	return len(b.b) - b.off
56}
57