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variablebyte.go
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variablebyte.go
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/*
* Copyright (c) 2013 Zhen, LLC. http://zhen.io. All rights reserved.
* Use of this source code is governed by the Apache 2.0 license.
*
*/
package variablebyte
import (
"errors"
"github.com/dataence/bytebuffer"
"github.com/vteromero/encoding"
"github.com/vteromero/encoding/cursor"
)
type VariableByte struct {
}
var _ encoding.Integer = (*VariableByte)(nil)
func New() encoding.Integer {
return &VariableByte{}
}
func (this *VariableByte) Compress(in []int32, inpos *cursor.Cursor, inlength int, out []int32, outpos *cursor.Cursor) error {
if inlength == 0 {
return errors.New("variablebyte/Compress: inlength = 0. No work done.")
}
//fmt.Printf("variablebyte/Compress: after inlength = %d\n", inlength)
buf := bytebuffer.NewByteBuffer(inlength * 8)
initoffset := int32(0)
tmpinpos := inpos.Get()
for _, v := range in[tmpinpos : tmpinpos+inlength] {
val := uint32(v - initoffset)
initoffset = v
for val >= 0x80 {
buf.Put(byte(val) | 0x80)
val >>= 7
}
buf.Put(byte(val))
}
for buf.Position()%4 != 0 {
//fmt.Printf("variablebyte/Compress: putting 128\n")
buf.Put(128)
}
length := buf.Position()
buf.Flip()
ibuf := buf.AsInt32Buffer()
//fmt.Printf("variablebyte/Compress: l = %d, outpos = %d, ibuf = %v, buf = %v\n", length/4, outpos.Get(), ibuf, buf)
err := ibuf.GetInt32s(out, outpos.Get(), length/4)
if err != nil {
//fmt.Printf("variablebyte/Compress: error with GetUint32s - %v\n", err)
return err
}
outpos.Add(length / 4)
inpos.Add(inlength)
//fmt.Printf("variablebyte/Compress: out = %v\n", out)
return nil
}
func (this *VariableByte) Uncompress(in []int32, inpos *cursor.Cursor, inlength int, out []int32, outpos *cursor.Cursor) error {
if inlength == 0 {
return errors.New("variablebyte/Uncompress: inlength = 0. No work done.")
}
//fmt.Printf("variablebyte/Uncompress: after inlength = %d\n", inlength)
s := uint(0)
p := inpos.Get()
finalp := inpos.Get() + inlength
tmpoutpos := outpos.Get()
initoffset := int32(0)
v := int32(0)
shift := uint(0)
for p < finalp {
c := in[p] >> (24 - s)
s += 8
if s == 32 {
s = 0
p += 1
}
v += ((c & 127) << shift)
if c&128 == 0 {
out[tmpoutpos] = v + initoffset
initoffset = out[tmpoutpos]
tmpoutpos += 1
v = 0
shift = 0
} else {
shift += 7
}
outpos.Set(tmpoutpos)
inpos.Add(inlength)
}
return nil
}