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authorDaniel J Walsh <dwalsh@redhat.com>2019-08-01 03:46:14 -0400
committerDaniel J Walsh <dwalsh@redhat.com>2019-08-01 03:46:14 -0400
commit9d6dce119949d340ebb42becae018a3c11148690 (patch)
treec0bb999f9bddbc9379f9f7b159194d35c077fb36 /vendor/github.com/klauspost/compress/fse/bitreader.go
parent39de184b8bfb14954f77190f0e6127c1ddc363c0 (diff)
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github.com/containers/storage v1.12.13
Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>
Diffstat (limited to 'vendor/github.com/klauspost/compress/fse/bitreader.go')
-rw-r--r--vendor/github.com/klauspost/compress/fse/bitreader.go107
1 files changed, 107 insertions, 0 deletions
diff --git a/vendor/github.com/klauspost/compress/fse/bitreader.go b/vendor/github.com/klauspost/compress/fse/bitreader.go
new file mode 100644
index 000000000..b9db204f5
--- /dev/null
+++ b/vendor/github.com/klauspost/compress/fse/bitreader.go
@@ -0,0 +1,107 @@
+// 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
+
+import (
+ "errors"
+ "io"
+)
+
+// bitReader reads a bitstream in reverse.
+// The last set bit indicates the start of the stream and is used
+// for aligning the input.
+type bitReader struct {
+ in []byte
+ off uint // next byte to read is at in[off - 1]
+ value uint64
+ bitsRead uint8
+}
+
+// init initializes and resets the bit reader.
+func (b *bitReader) init(in []byte) error {
+ if len(in) < 1 {
+ return errors.New("corrupt stream: too short")
+ }
+ b.in = in
+ b.off = uint(len(in))
+ // The highest bit of the last byte indicates where to start
+ v := in[len(in)-1]
+ if v == 0 {
+ return errors.New("corrupt stream, did not find end of stream")
+ }
+ b.bitsRead = 64
+ b.value = 0
+ b.fill()
+ b.fill()
+ b.bitsRead += 8 - uint8(highBits(uint32(v)))
+ return nil
+}
+
+// getBits will return n bits. n can be 0.
+func (b *bitReader) getBits(n uint8) uint16 {
+ if n == 0 || b.bitsRead >= 64 {
+ return 0
+ }
+ return b.getBitsFast(n)
+}
+
+// getBitsFast requires that at least one bit is requested every time.
+// There are no checks if the buffer is filled.
+func (b *bitReader) getBitsFast(n uint8) uint16 {
+ const regMask = 64 - 1
+ v := uint16((b.value << (b.bitsRead & regMask)) >> ((regMask + 1 - n) & regMask))
+ b.bitsRead += n
+ return v
+}
+
+// fillFast() will make sure at least 32 bits are available.
+// There must be at least 4 bytes available.
+func (b *bitReader) fillFast() {
+ if b.bitsRead < 32 {
+ return
+ }
+ // Do single re-slice to avoid bounds checks.
+ v := b.in[b.off-4 : b.off]
+ low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+ b.value = (b.value << 32) | uint64(low)
+ b.bitsRead -= 32
+ b.off -= 4
+}
+
+// fill() will make sure at least 32 bits are available.
+func (b *bitReader) fill() {
+ if b.bitsRead < 32 {
+ return
+ }
+ if b.off > 4 {
+ v := b.in[b.off-4 : b.off]
+ low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+ b.value = (b.value << 32) | uint64(low)
+ b.bitsRead -= 32
+ b.off -= 4
+ return
+ }
+ for b.off > 0 {
+ b.value = (b.value << 8) | uint64(b.in[b.off-1])
+ b.bitsRead -= 8
+ b.off--
+ }
+}
+
+// finished returns true if all bits have been read from the bit stream.
+func (b *bitReader) finished() bool {
+ return b.off == 0 && b.bitsRead >= 64
+}
+
+// close the bitstream and returns an error if out-of-buffer reads occurred.
+func (b *bitReader) close() error {
+ // Release reference.
+ b.in = nil
+ if b.bitsRead > 64 {
+ return io.ErrUnexpectedEOF
+ }
+ return nil
+}