compress/fse/bytereader.go

// Copyright 2018 Klaus Post. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Based on work Copyright (c) 2013, Yann Collet, released under BSD License.

package fse

// byteReader provides a byte reader that reads
// little endian values from a byte stream.
// The input stream is manually advanced.
// The reader performs no bounds checks.
type byteReader struct {
	b   []byte
	off int
}

// init will initialize the reader and set the input.
func (b *byteReader) init(in []byte) {
	b.b = in
	b.off = 0
}

// advance the stream b n bytes.
func (b *byteReader) advance(n uint) {
	b.off += int(n)
}

// Int32 returns a little endian int32 starting at current offset.
func (b byteReader) Int32() int32 {
	b2 := b.b[b.off : b.off+4 : b.off+4]
	v3 := int32(b2[3])
	v2 := int32(b2[2])
	v1 := int32(b2[1])
	v0 := int32(b2[0])
	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
}

// Uint32 returns a little endian uint32 starting at current offset.
func (b byteReader) Uint32() uint32 {
	b2 := b.b[b.off : b.off+4 : b.off+4]
	v3 := uint32(b2[3])
	v2 := uint32(b2[2])
	v1 := uint32(b2[1])
	v0 := uint32(b2[0])
	return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
}

// unread returns the unread portion of the input.
func (b byteReader) unread() []byte {
	return b.b[b.off:]
}

// remain will return the number of bytes remaining.
func (b byteReader) remain() int {
	return len(b.b) - b.off
}