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}
// 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)
input []byte
err error
flags, predicted byte
rc, total, copied int
)
// Read the next prediction header
readHeader:
rc, err = ctx.source.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
}
// 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 {
// Retry the read if we have fewer bytes than what the prediction header indicates
var r int
r, err = ctx.source.Read(ctx.input[int(predicted)+rc:])
rc += r
goto retryData
} // Continue on any error, try to decompress and return it along the result
// rc now contains the amount of actual bytes in this cycle (usually 8)
rc += int(predicted)
// Walk the buffer, filling in the predicted blanks,
// relocating read bytes and and updating the guess table
for i, a := 0, predicted; i < rc; i++ {
if (flags & (1 << uint(i))) > 0 {
// Guess succeeded, fill in from the table
ctx.input[i] = ctx.table[ctx.hash]
} else {
// Relocate a read byte and advance the read byte index
ctx.input[i], a = ctx.input[a], a+1
// Guess failed, update the table
ctx.table[ctx.hash] = ctx.input[i]
}
// Update the hash
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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}
// 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
return iou.SizedReader(&dcmp, 8)
}
type decompressor struct {
context
source io.Reader
}
// Note: this method does not implement the full io.Reader's Read() semantics
func (ctx *decompressor) Read(output []byte) (int, error) {
var (
err error
buffer []byte = make([]byte, 8)
flags byte
predicted, rc, total, copied int
)
// Read the next prediction header
readHeader:
rc, err = ctx.source.Read(buffer[:1])
// 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 = buffer[0]
predicted = bits.Hamming(flags)
// Read the non-predicted bytes and place them in the end of the buffer
rc, err = ctx.source.Read(buffer[predicted:])
retryData:
if (rc < (8 - predicted)) && err == nil {
// Retry the read if we have fewer bytes than what the prediction header indicates
var r int
r, err = ctx.source.Read(buffer[predicted+rc:])
rc += r
goto retryData
} // Continue on any error, try to decompress and return it along the result
// rc now contains the amount of actual bytes in this cycle (usually 8)
rc += predicted
// Walk the buffer, filling in the predicted blanks,
// relocating read bytes and and updating the guess table
for i, a := 0, predicted; i < rc; i++ {
if (flags & (1 << uint(i))) > 0 {
// Guess succeeded, fill in from the table
buffer[i] = ctx.table[ctx.hash]
} else {
// Relocate a read byte and advance the read byte index
buffer[i], a = buffer[a], a+1
// Guess failed, update the table
ctx.table[ctx.hash] = buffer[i]
}
// Update the hash
ctx.update(buffer[i])
}
// Copy the decompressed data to the output and accumulate the count
copied = copy(output, buffer[: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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