Copyright 2011 The Go Authors. All rights reserved. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.

package bzip2
moveToFrontDecoder implements a move-to-front list. Such a list is an efficient way to transform a string with repeating elements into one with many small valued numbers, which is suitable for entropy encoding. It works by starting with an initial list of symbols and references symbols by their index into that list. When a symbol is referenced, it's moved to the front of the list. Thus, a repeated symbol ends up being encoded with many zeros, as the symbol will be at the front of the list after the first access.
type moveToFrontDecoder []byte
newMTFDecoder creates a move-to-front decoder with an explicit initial list of symbols.
func ( []byte) moveToFrontDecoder {
	if len() > 256 {
		panic("too many symbols")
	}
	return moveToFrontDecoder()
}
newMTFDecoderWithRange creates a move-to-front decoder with an initial symbol list of 0...n-1.
func ( int) moveToFrontDecoder {
	if  > 256 {
		panic("newMTFDecoderWithRange: cannot have > 256 symbols")
	}

	 := make([]byte, )
	for  := 0;  < ; ++ {
		[] = byte()
	}
	return moveToFrontDecoder()
}
Implement move-to-front with a simple copy. This approach beats more sophisticated approaches in benchmarking, probably because it has high locality of reference inside of a single cache line (most move-to-front operations have n < 64).
	 = []
	copy([1:], [:])
	[0] = 
	return
}
First returns the symbol at the front of the list.
func ( moveToFrontDecoder) () byte {
	return [0]