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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
readCount, available int
)
// Sanity check for space to read into
if len(output) == 0 {
return 0, nil
}
// Check whether we have leftover data in the buffer
if len(ctx.input) > 0 {
readCount = copy(output, ctx.input)
// Check whether we still have leftover data in the buffer :)
if readCount < len(ctx.input) {
ctx.input = ctx.input[:copy(ctx.input, ctx.input[readCount:])]
}
return readCount, nil
}
// Read the next prediction header
readCount, err = reader.Read(ctx.input[:1])
// Fail on error unless it is EOF
if err != nil && err != io.EOF {
return 0, err
} else if readCount == 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]
available = 8 - int(bits.Hamming(flags))
// Read the non-predicted bytes according to header.
readCount, err = reader.Read(ctx.input[:available])
retryData:
if readCount < int(available) && err == nil {
// Retry the read if we have fewer bytes than what the prediction header indicates
var rc int
rc, err = reader.Read(ctx.input[readCount:available])
readCount += rc
goto retryData
} // Continue on any error, try to decompress and return it along the result
// Spread the read bytes right to left to avoid overlapping
for i, a := 7, available-1; i >= 0; i-- {
if ((flags >> uint(i)) & 1) == 0 {
ctx.input[i] = ctx.input[a]
a--
}
}
// Walk the buffer, fill in the predicted blanks and update the guess table
for i := uint(0); i < 8; i++ {
readCount++
} else {
// Guess failed, update the table
ctx.table[ctx.hash] = ctx.input[i]
}
// Update the hash
ctx.hash = (ctx.hash << 4) ^ uint16(ctx.input[i])
}
// readCount now contains the precise amount of populated data
ctx.input = ctx.input[:readCount]
available = copy(output, ctx.input)
// Check for remaining bytes that dont fit in the output buffer
if available < readCount {
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 int
)
// Sanity check for space to read into
if len(output) == 0 {
return 0, nil
}
// Check whether we have leftover data in the buffer
if len(ctx.input) > 0 {
rc = copy(output, ctx.input)
// Check whether we still have leftover data in the buffer :)
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))
available = 8 - predicted
// Read the non-predicted bytes and place them in the end of the buffer
rc, err = reader.Read(ctx.input[predicted:])
retryData:
if rc < int(available) && err == nil {
// Retry the read if we have fewer bytes than what the prediction header indicates
var rc int
rc, err = reader.Read(ctx.input[predicted+rc:])
rc += rc
goto retryData
} // Continue on any error, try to decompress and return it along the result
// Walk the buffer, filling in the predicted blanks,
// relocating read bytes and and updating the guess table
for i, a := uint(0), predicted; i < 8; i++ {
if (flags & (1 << i)) > 0 {
// Guess succeeded, fill in from the table
ctx.input[i] = ctx.table[ctx.hash]
rc++
} else {
// Relocate a read byte
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.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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