Check-in [42ba1f458d]
Overview
Comment:Decompressor - try to fill as much as possible in the output buffer in a single pass.
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Files: files | file ages | folders
SHA1:42ba1f458d7b62fd3cc81c27cf27ff4147cb5cdf
User & Date: spaskalev on 2014-12-22 16:35:06
Other Links: manifest | tags
Context
2014-12-22
16:41
Integrate the decompressor2 branch into trunk now that it is faster. check-in: 6d10a1d28f user: spaskalev tags: trunk
16:35
Decompressor - try to fill as much as possible in the output buffer in a single pass. Closed-Leaf check-in: 42ba1f458d user: spaskalev tags: decompressor2
15:34
Fixed a nasty variable shadowing bug :) check-in: e9b80a705b user: spaskalev tags: decompressor2
Changes

Modified src/0dev.org/predictor/predictor.go from [219e9c8a2d] to [71e92568a2].

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// and decompresses data according to the predictor algorithm
func Decompressor(reader io.Reader) io.Reader {
	var ctx context
	ctx.input = make([]byte, 0, 8)

	return decompressor(func(output []byte) (int, error) {
		var (
			err                      error
			flags                    byte
			rc, available, predicted int
		)

		// Sanity check for space to read into
		if len(output) == 0 {
			return 0, nil
		}

................................................................................
			if rc < len(ctx.input) {
				ctx.input = ctx.input[:copy(ctx.input, ctx.input[rc:])]
			}
			return rc, nil
		}

		// Read the next prediction header

		rc, err = reader.Read(ctx.input[:1])
		// Fail on error unless it is EOF
		if err != nil && err != io.EOF {
			return 0, err
		} else if rc == 0 {
			return 0, 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 = int(bits.Hamming(flags))
................................................................................
			// Update the hash
			ctx.hash = (ctx.hash << 4) ^ uint16(ctx.input[i])
		}

		// rc now contains the precise amount of populated data
		ctx.input = ctx.input[:rc]
		available = copy(output, ctx.input)



		// Check for remaining bytes that dont fit in the output buffer
		if available < rc {
			ctx.input = ctx.input[:copy(ctx.input, ctx.input[available:])]
		} else {
			// Clear the buffer
			ctx.input = ctx.input[:0]
		}






		return available, err
	})
}







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// and decompresses data according to the predictor algorithm
func Decompressor(reader io.Reader) io.Reader {
	var ctx context
	ctx.input = make([]byte, 0, 8)

	return decompressor(func(output []byte) (int, error) {
		var (
			err                             error
			flags                           byte
			rc, available, predicted, total int
		)

		// Sanity check for space to read into
		if len(output) == 0 {
			return 0, nil
		}

................................................................................
			if rc < len(ctx.input) {
				ctx.input = ctx.input[:copy(ctx.input, ctx.input[rc:])]
			}
			return rc, nil
		}

		// Read the next prediction header
	readHeader:
		rc, err = reader.Read(ctx.input[:1])
		// 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 = int(bits.Hamming(flags))
................................................................................
			// Update the hash
			ctx.hash = (ctx.hash << 4) ^ uint16(ctx.input[i])
		}

		// rc now contains the precise amount of populated data
		ctx.input = ctx.input[:rc]
		available = copy(output, ctx.input)

		total += available

		// Check for remaining bytes that dont fit in the output buffer
		if available < rc {
			ctx.input = ctx.input[:copy(ctx.input, ctx.input[available:])]
		} else {
			// Clear the buffer
			ctx.input = ctx.input[:0]

			output = output[available:]
			if len(output) > 0 && err == nil {
				goto readHeader
			}
		}

		return total, err
	})
}