/
directpackedreader.go
174 lines (151 loc) · 3.53 KB
/
directpackedreader.go
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package packed
import (
"context"
"errors"
"github.com/geange/lucene-go/core/store"
"io"
"math"
)
var _ Reader = &DirectPackedReader{}
// DirectPackedReader
// Reads directly from disk on each get
// just for back compat, use DirectReader/DirectWriter for more efficient impl
type DirectPackedReader struct {
in store.IndexInput
bitsPerValue int
startPointer int64
valueMask uint64
valueCount int
}
func (d *DirectPackedReader) GetBulk(index int, arr []uint64) int {
for i := range arr {
n, err := d.Get(index + i)
if err != nil {
if errors.Is(err, io.EOF) {
return i
}
return 0
}
arr[i] = n
}
return len(arr)
}
func (d *DirectPackedReader) Size() int {
return d.valueCount
}
func NewDirectPackedReader(bitsPerValue, valueCount int, in store.IndexInput) *DirectPackedReader {
reader := &DirectPackedReader{
in: in,
bitsPerValue: bitsPerValue,
startPointer: in.GetFilePointer(),
valueCount: valueCount,
}
if bitsPerValue == 64 {
reader.valueMask = math.MaxUint64
} else {
reader.valueMask = (1 << bitsPerValue) - 1
}
return reader
}
func (d *DirectPackedReader) Get(index int) (uint64, error) {
majorBitPos := index * d.bitsPerValue
elementPos := int64(majorBitPos >> 3)
if _, err := d.in.Seek(d.startPointer+elementPos, io.SeekStart); err != nil {
return 0, err
}
bitPos := majorBitPos & 7
// round up bits to a multiple of 8 to find total bytes needed to read
// 将位数四舍五入到8的倍数,以找到读取所需的总字节数
// roundedBits = (bitPos+d.bitsPerValue+7) / 8
roundedBits := int(uint64(bitPos+d.bitsPerValue+7) & (^uint64(7)))
// the number of extra bits read at the end to shift out
shiftRightBits := roundedBits - bitPos - d.bitsPerValue
var rawValue uint64
ctx := context.TODO()
switch roundedBits >> 3 {
case 1:
v, err := d.in.ReadByte()
if err != nil {
return 0, err
}
rawValue = uint64(v)
case 2:
v, err := d.in.ReadUint16(ctx)
if err != nil {
return 0, err
}
rawValue = uint64(v)
case 3:
n1, err := d.in.ReadUint16(ctx)
if err != nil {
return 0, err
}
n2, err := d.in.ReadByte()
if err != nil {
return 0, err
}
rawValue = uint64(n1)<<8 | uint64(n2)
case 4:
v, err := d.in.ReadUint32(ctx)
if err != nil {
return 0, err
}
rawValue = uint64(v)
case 5:
n1, err := d.in.ReadUint32(ctx)
if err != nil {
return 0, err
}
n2, err := d.in.ReadByte()
if err != nil {
return 0, err
}
rawValue = uint64(n1)<<8 | uint64(n2)
case 6:
n1, err := d.in.ReadUint32(ctx)
if err != nil {
return 0, err
}
n2, err := d.in.ReadUint16(ctx)
if err != nil {
return 0, err
}
rawValue = uint64(n1)<<16 | uint64(n2)
case 7:
n1, err := d.in.ReadUint32(ctx)
if err != nil {
return 0, err
}
n2, err := d.in.ReadUint16(ctx)
if err != nil {
return 0, err
}
n3, err := d.in.ReadByte()
if err != nil {
return 0, err
}
rawValue = uint64(n1)<<24 | uint64(n2)<<8 | uint64(n3)
case 8:
v, err := d.in.ReadUint64(ctx)
if err != nil {
return 0, err
}
rawValue = v
case 9:
// We must be very careful not to shift out relevant bits. So we account for right shift
// we would normally do on return here, and reset it.
n1, err := d.in.ReadUint64(ctx)
if err != nil {
return 0, err
}
n2, err := d.in.ReadByte()
if err != nil {
return 0, err
}
rawValue = n1<<(8-shiftRightBits) | uint64(n2)>>shiftRightBits
shiftRightBits = 0
default:
return 0, errors.New("bitsPerValue too large")
}
return (rawValue >> shiftRightBits) & d.valueMask, nil
}