89 lines
2.0 KiB
Go
89 lines
2.0 KiB
Go
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// Copyright 2019+ Klaus Post. All rights reserved.
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// License information can be found in the LICENSE file.
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// Based on work by Yann Collet, released under BSD License.
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package zstd
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// byteReader provides a byte reader that reads
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// little endian values from a byte stream.
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// The input stream is manually advanced.
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// The reader performs no bounds checks.
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type byteReader struct {
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b []byte
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off int
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}
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// init will initialize the reader and set the input.
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func (b *byteReader) init(in []byte) {
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b.b = in
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b.off = 0
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}
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// advance the stream b n bytes.
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func (b *byteReader) advance(n uint) {
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b.off += int(n)
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}
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// overread returns whether we have advanced too far.
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func (b *byteReader) overread() bool {
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return b.off > len(b.b)
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}
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// Int32 returns a little endian int32 starting at current offset.
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func (b byteReader) Int32() int32 {
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b2 := b.b[b.off:]
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b2 = b2[:4]
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v3 := int32(b2[3])
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v2 := int32(b2[2])
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v1 := int32(b2[1])
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v0 := int32(b2[0])
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return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
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}
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// Uint8 returns the next byte
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func (b *byteReader) Uint8() uint8 {
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v := b.b[b.off]
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return v
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}
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// Uint32 returns a little endian uint32 starting at current offset.
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func (b byteReader) Uint32() uint32 {
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if r := b.remain(); r < 4 {
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// Very rare
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v := uint32(0)
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for i := 1; i <= r; i++ {
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v = (v << 8) | uint32(b.b[len(b.b)-i])
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}
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return v
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}
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b2 := b.b[b.off:]
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b2 = b2[:4]
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v3 := uint32(b2[3])
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v2 := uint32(b2[2])
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v1 := uint32(b2[1])
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v0 := uint32(b2[0])
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return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
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}
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// Uint32NC returns a little endian uint32 starting at current offset.
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// The caller must be sure if there are at least 4 bytes left.
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func (b byteReader) Uint32NC() uint32 {
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b2 := b.b[b.off:]
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b2 = b2[:4]
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v3 := uint32(b2[3])
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v2 := uint32(b2[2])
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v1 := uint32(b2[1])
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v0 := uint32(b2[0])
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return v0 | (v1 << 8) | (v2 << 16) | (v3 << 24)
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}
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// unread returns the unread portion of the input.
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func (b byteReader) unread() []byte {
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return b.b[b.off:]
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}
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// remain will return the number of bytes remaining.
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func (b byteReader) remain() int {
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return len(b.b) - b.off
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}
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