/usr/share/gocode/src/github.com/influxdata/influxdb/tsdb/engine/tsm1/bit_reader.go is in golang-github-influxdb-influxdb-dev 1.1.1+dfsg1-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 | package tsm1
import "io"
// BitReader reads bits from an io.Reader.
type BitReader struct {
data []byte
buf struct {
v uint64 // bit buffer
n uint // available bits
}
}
// NewBitReader returns a new instance of BitReader that reads from data.
func NewBitReader(data []byte) *BitReader {
b := new(BitReader)
b.Reset(data)
return b
}
// Reset sets the underlying reader on b and reinitializes.
func (r *BitReader) Reset(data []byte) {
r.data = data
r.buf.v, r.buf.n = 0, 0
r.readBuf()
}
// CanReadBitFast returns true if calling ReadBitFast() is allowed.
// Fast bit reads are allowed when at least 2 values are in the buffer.
// This is because it is not required to refilled the buffer and the caller
// can inline the calls.
func (r *BitReader) CanReadBitFast() bool { return r.buf.n > 1 }
// ReadBitFast is an optimized bit read.
// IMPORTANT: Only allowed if CanReadFastBit() is true!
func (r *BitReader) ReadBitFast() bool {
v := (r.buf.v&(1<<63) != 0)
r.buf.v <<= 1
r.buf.n -= 1
return v
}
// ReadBit returns the next bit from the underlying data.
func (r *BitReader) ReadBit() (bool, error) {
v, err := r.ReadBits(1)
return v != 0, err
}
// ReadBits reads nbits from the underlying data.
func (r *BitReader) ReadBits(nbits uint) (uint64, error) {
// Return EOF if there is no more data.
if r.buf.n == 0 {
return 0, io.EOF
}
// Return bits from buffer if less than available bits.
if nbits <= r.buf.n {
// Return all bits, if requested.
if nbits == 64 {
v := r.buf.v
r.buf.v, r.buf.n = 0, 0
r.readBuf()
return v, nil
}
// Otherwise mask returned bits.
v := (r.buf.v >> (64 - nbits))
r.buf.v <<= nbits
r.buf.n -= nbits
if r.buf.n == 0 {
r.readBuf()
}
return v, nil
}
// Otherwise read all available bits in current buffer.
v, n := r.buf.v, r.buf.n
// Read new buffer.
r.buf.v, r.buf.n = 0, 0
r.readBuf()
// Append new buffer to previous buffer and shift to remove unnecessary bits.
v |= (r.buf.v >> n)
v >>= 64 - nbits
// Remove used bits from new buffer.
bufN := nbits - n
if bufN > r.buf.n {
bufN = r.buf.n
}
r.buf.v <<= bufN
r.buf.n -= bufN
if r.buf.n == 0 {
r.readBuf()
}
return v, nil
}
func (r *BitReader) readBuf() {
// Determine number of bytes to read to fill buffer.
byteN := 8 - (r.buf.n / 8)
// Limit to the length of our data.
if n := uint(len(r.data)); byteN > n {
byteN = n
}
// Optimized 8-byte read.
if byteN == 8 {
r.buf.v = uint64(r.data[7]) | uint64(r.data[6])<<8 |
uint64(r.data[5])<<16 | uint64(r.data[4])<<24 |
uint64(r.data[3])<<32 | uint64(r.data[2])<<40 |
uint64(r.data[1])<<48 | uint64(r.data[0])<<56
r.buf.n = 64
r.data = r.data[8:]
return
}
// Otherwise append bytes to buffer.
for i := uint(0); i < byteN; i++ {
r.buf.n += 8
r.buf.v |= uint64(r.data[i]) << (64 - r.buf.n)
}
// Move data forward.
r.data = r.data[byteN:]
}
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