Overview
| Comment: | Predictor's compressor and decompressor structures now implement io.Writer/io.Reader in order to deal away with function indirection but they do not follow the required semantics. Those are provided by the SizedWriter/SizedReader wrappers returned by the constructor functions. |
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| SHA1: |
4dfcff962c763b560a5af8101c2f3f3a |
| User & Date: | spaskalev on 2014-12-25 00:55:43 |
| Other Links: | manifest | tags |
Context
|
2014-12-25
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| 01:25 | Removed pdc's output buffer when decompressing as io.Copy uses a sufficiently-large buffer internally. check-in: 2b1ed8e45e user: spaskalev tags: trunk | |
| 00:55 | Predictor's compressor and decompressor structures now implement io.Writer/io.Reader in order to deal away with function indirection but they do not follow the required semantics. Those are provided by the SizedWriter/SizedReader wrappers returned by the constructor functions. check-in: 4dfcff962c user: spaskalev tags: trunk | |
| 00:43 | Extracted predictor's compressor and decompressor code into separate structs that embed Sized{Writer,Reader} check-in: 50507bd510 user: spaskalev tags: trunk | |
Changes
Modified src/0dev.org/predictor/predictor.go from [cb877636af] to [3161320c11].
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// Returns an io.Writer implementation that wraps the provided io.Writer
// and compresses data according to the predictor algorithm
//
// It can buffer data as the predictor mandates 8-byte blocks with a header.
// A call with no data will force a flush.
func Compressor(writer io.Writer) io.Writer {
var cmp compressor
cmp.Writer = iou.SizedWriter(iou.WriterFunc(cmp.compress), 8)
cmp.target = writer
return &cmp
}
type compressor struct {
context
io.Writer
target io.Writer
}
func (ctx *compressor) compress(data []byte) (int, error) {
var (
blockSize int = 8
datalength int = len(data)
)
if datalength == 0 {
return 0, nil
................................................................................
return datalength, nil
}
// Returns an io.Reader implementation that wraps the provided io.Reader
// and decompresses data according to the predictor algorithm
func Decompressor(reader io.Reader) io.Reader {
var dcmp decompressor
dcmp.Reader = iou.SizedReader(iou.ReaderFunc(dcmp.decompress), 8)
dcmp.source = reader
dcmp.input = make([]byte, 0, 8)
return &dcmp
}
type decompressor struct {
context
io.Reader
source io.Reader
input []byte
}
func (ctx *decompressor) decompress(output []byte) (int, error) {
var (
err error
flags, predicted byte
rc, total, copied int
)
// Read the next prediction header
................................................................................
// Fail on error unless it is EOF
if err != nil && err != io.EOF {
return total, err
} else if rc == 0 {
return total, err
}
// Extend the buffer, copy the prediction header
// and calculate the number of subsequent bytes to read
ctx.input = ctx.input[:8]
flags = ctx.input[0]
predicted = bits.Hamming(flags)
// Read the non-predicted bytes and place them in the end of the buffer
rc, err = ctx.source.Read(ctx.input[predicted:])
retryData:
if rc < int(8-predicted) && err == nil {
................................................................................
ctx.update(ctx.input[i])
}
// Copy the decompressed data to the output and accumulate the count
copied = copy(output, ctx.input[:rc])
total += copied
// Clear the buffer
ctx.input = ctx.input[:0]
// Loop for another pass if there is available space in the output
output = output[copied:]
if len(output) > 0 && err == nil {
goto readHeader
}
return total, err
}
|
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// Returns an io.Writer implementation that wraps the provided io.Writer
// and compresses data according to the predictor algorithm
//
// It can buffer data as the predictor mandates 8-byte blocks with a header.
// A call with no data will force a flush.
func Compressor(writer io.Writer) io.Writer {
var cmp compressor
cmp.target = writer
return iou.SizedWriter(&cmp, 8)
}
type compressor struct {
context
target io.Writer
}
// Note: this method does not implement the full io.Writer's Write() semantics
func (ctx *compressor) Write(data []byte) (int, error) {
var (
blockSize int = 8
datalength int = len(data)
)
if datalength == 0 {
return 0, nil
................................................................................
return datalength, nil
}
// Returns an io.Reader implementation that wraps the provided io.Reader
// and decompresses data according to the predictor algorithm
func Decompressor(reader io.Reader) io.Reader {
var dcmp decompressor
dcmp.source = reader
dcmp.input = make([]byte, 8)
return iou.SizedReader(&dcmp, 8)
}
type decompressor struct {
context
source io.Reader
input []byte
}
// Note: this method does not implement the full io.Reader's Read() semantics
func (ctx *decompressor) Read(output []byte) (int, error) {
var (
err error
flags, predicted byte
rc, total, copied int
)
// Read the next prediction header
................................................................................
// Fail on error unless it is EOF
if err != nil && err != io.EOF {
return total, err
} else if rc == 0 {
return total, err
}
// Copy the prediction header and calculate the number of subsequent bytes to read
flags = ctx.input[0]
predicted = bits.Hamming(flags)
// Read the non-predicted bytes and place them in the end of the buffer
rc, err = ctx.source.Read(ctx.input[predicted:])
retryData:
if rc < int(8-predicted) && err == nil {
................................................................................
ctx.update(ctx.input[i])
}
// Copy the decompressed data to the output and accumulate the count
copied = copy(output, ctx.input[:rc])
total += copied
// Loop for another pass if there is available space in the output
output = output[copied:]
if len(output) > 0 && err == nil {
goto readHeader
}
return total, err
}
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