#### Bzip2 Implementation
#### Copyright (C) 2023-2024 Remilia Scarlet
#### Copyright (C) 2015 Jaime Olivares
#### Copyright (c) 2011 Matthew Francis
#### MIT License
####
#### Ported from the Java implementation by Matthew Francis:
#### https://github.com/MateuszBartosiewicz/bzip2.
####
#### Ported by Remilia Scarlet from the C# implementation by Jamie Olivares:
#### http://github.com/jaime-olivares/bzip2
module RemiLib::Compression::BZip2
# A 256 entry Move-to-Front transformer.
private class MoveToFront
@mtf : Array(UInt8)
# Creates a new `MoveToFront` instance.
def initialize
@mtf = Array(UInt8).new(256, &.to_u8!)
end
# Moves `value` to the head of the MTF list (forward Move To Front
# transform). Returns the position the value moved from.
@[AlwaysInline]
def valueToFront(value : UInt8) : Int32
index : Int32 = 0
tmp : UInt8 = @mtf.unsafe_fetch(0)
tmp2 : UInt8 = 0
unless value == tmp
@mtf.unsafe_put(0, value)
while value != tmp
index += 1
tmp2 = tmp
tmp = @mtf.unsafe_fetch(index)
@mtf.unsafe_put(index, tmp2)
end
end
index
end
# Gets the value at `index` and moves it to the front of the MTF list
# (inverse Move To Front transform). This returns the value at the given
# `index`.
@[AlwaysInline]
def indexToFront(index : Int32) : UInt8
ret = @mtf[index]
@mtf[1, index] = @mtf[0, index]
@mtf.unsafe_put(0, ret)
ret
end
end
end
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