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Comment:Extracted SizedReader to a sizedReader type with a Read() method. Closures seem to be slower in Go 1.4 and there is no real need for SizedReader to be a closure.
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SHA1: b703c38e0b59db785a1706b2920f0ee6ff120ad3
User & Date: spaskalev on 2014-12-24 23:45:57.234
Other Links: manifest | tags
Context
2014-12-24
23:58
0dev.org/ioutil/SizedReader is now as fast as bufio.Reader if not faster for a buffer of 4096 bytes. Switched pdc to use it for decompression buffering and removed profiling code from the former check-in: 2cec92909f user: spaskalev tags: trunk
23:45
Extracted SizedReader to a sizedReader type with a Read() method. Closures seem to be slower in Go 1.4 and there is no real need for SizedReader to be a closure. check-in: b703c38e0b user: spaskalev tags: trunk
23:33
Made SizedReader faster by keeping explicit buffer indices. check-in: 701ac713de user: spaskalev tags: trunk
Changes
Unified Diff Ignore Whitespace Patch
Modified src/0dev.org/commands/pdc/main.go from [1dda5424c0] to [675059111f]. 
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package main

import (

	iou "0dev.org/ioutil"
	predictor "0dev.org/predictor"
	"bufio"
	"fmt"
	"io"
	"os"
)

func main() {

	switch {
	case len(os.Args) == 1:
		os.Exit(compress(os.Stdout, os.Stdin))
	case len(os.Args) == 2 && os.Args[1] == "-d":
		os.Exit(decompress(os.Stdout, os.Stdin))
	default:
		fmt.Fprintln(os.Stdout, "Usage: pdc [-d]")
	}




}

// Compress the data from the given io.Reader and write it to the given io.Writer
// I/O is buffered for better performance
func compress(output io.Writer, input io.Reader) int {
	var (
		err        error




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package main

import (
	pprof "0dev.org/debug/pprof"
	iou "0dev.org/ioutil"
	predictor "0dev.org/predictor"
	// "bufio"
	"fmt"
	"io"
	"os"
)

func main() {
	var code int
	switch {
	case len(os.Args) == 1:
		code = compress(os.Stdout, os.Stdin)
	case len(os.Args) == 2 && os.Args[1] == "-d":
		code = decompress(os.Stdout, os.Stdin)
	default:
		fmt.Fprintln(os.Stdout, "Usage: pdc [-d]")
	}

	pprof.Stop()

	os.Exit(code)
}

// Compress the data from the given io.Reader and write it to the given io.Writer
// I/O is buffered for better performance
func compress(output io.Writer, input io.Reader) int {
	var (
		err        error
︙︙
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// Decompress the data from the given io.Reader and write it to the given io.Writer
// I/O is buffered for better performance
func decompress(output io.Writer, input io.Reader) int {
	var (
		err          error
		buffer       io.Writer = iou.SizedWriter(output, 4096)

		decompressor io.Reader = predictor.Decompressor(bufio.NewReader(input))
	)

	_, err = io.Copy(buffer, decompressor)
	if err != nil {
		fmt.Fprintln(os.Stderr, "Error while decompressing.\n", err)
		return 1
	}








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// Decompress the data from the given io.Reader and write it to the given io.Writer
// I/O is buffered for better performance
func decompress(output io.Writer, input io.Reader) int {
	var (
		err          error
		buffer       io.Writer = iou.SizedWriter(output, 4096)
		decompressor io.Reader = predictor.Decompressor(iou.SizedReader(input, 4096))
		//decompressor io.Reader = predictor.Decompressor(bufio.NewReader(input))
	)

	_, err = io.Copy(buffer, decompressor)
	if err != nil {
		fmt.Fprintln(os.Stderr, "Error while decompressing.\n", err)
		return 1
	}
︙︙
Modified src/0dev.org/ioutil/ioutil.go from [e5419d451e] to [c84493a1fe].
︙︙
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		// Handle the rest of the input
		return write(input[count:])
	}

	return write
}







// Returns a reader that delegates calls to Read(...) while ensuring
// that the output buffer is never smaller than the required size
// and is downsized to a multiple of the required size if larger.
func SizedReader(reader io.Reader, size int) io.Reader {
	var (

		buffer   []byte = make([]byte, size)
		from, to int    = 0, 0
	)



	return ReaderFunc(func(output []byte) (int, error) {
		var (
			count int
			err   error
		)

	start:
		// Reply with the buffered data if there is any
		if to-from > 0 {
			count = copy(output, buffer[from:to])

			// Advance the data in the buffer
			from += count

			// Check whether we have reached the end of the buffer
			if to-from == 0 {
				// Reset the buffer
				from, to = 0, 0

				return count, err
			}

			// Do not propagate an error until the buffer is exhausted
			return count, nil
		}

		// Delegate if the buffer is empty and the destination buffer is large enough
		if len(output) >= size {
			return reader.Read(output[:(len(output)/size)*size])
		}

		// Perform a read into the buffer
		count, err = reader.Read(buffer)

		// Size the buffer down to the read data size
		// and restart if we have successfully read some bytes
		from, to = 0, count
		if to-from > 0 {
			goto start
		}

		// Returning on err/misbehaving noop reader
		return 0, err
	})
}








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		// Handle the rest of the input
		return write(input[count:])
	}

	return write
}

type sizedReader struct {
	reader         io.Reader
	buffer         []byte
	from, to, size int
}

// Returns a reader that delegates calls to Read(...) while ensuring
// that the output buffer is never smaller than the required size
// and is downsized to a multiple of the required size if larger.
func SizedReader(reader io.Reader, size int) io.Reader {
	var sr sizedReader
	sr.reader = reader
	sr.buffer = make([]byte, size)
	sr.size, sr.from, sr.to = size, 0, 0

	return &sr
}

func (sr *sizedReader) Read(output []byte) (int, error) {
	var (
		count int
		err   error
	)

start:
	// Reply with the buffered data if there is any
	if sr.to-sr.from > 0 {
		count = copy(output, sr.buffer[sr.from:sr.to])

		// Advance the data in the buffer
		sr.from += count

		// Check whether we have reached the end of the buffer
		if sr.to-sr.from == 0 {
			// Reset the buffer
			sr.from, sr.to = 0, 0

			return count, err
		}

		// Do not propagate an error until the buffer is exhausted
		return count, nil
	}

	// Delegate if the buffer is empty and the destination buffer is large enough
	if len(output) >= sr.size {
		return sr.reader.Read(output[:(len(output)/sr.size)*sr.size])
	}

	// Perform a read into the buffer
	count, err = sr.reader.Read(sr.buffer)

	// Size the buffer down to the read data size
	// and restart if we have successfully read some bytes
	sr.from, sr.to = 0, count
	if sr.to-sr.from > 0 {
		goto start
	}

	// Returning on err/misbehaving noop reader
	return 0, err

}
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