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Added some comments and corrected decode literal part of lzma main cycle.

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This commit is contained in:
Timofey Solomko
2016-12-16 22:19:18 +03:00
parent 85d2c0f7a4
commit 843dadf08c
1 changed files with 23 additions and 6 deletions
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Sources/LZMA.swift
+23 -6
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@@ -61,7 +61,6 @@ public final class LZMA: DecompressionAlgorithm {
self.isFull = false
}
/// Don't forget to put byte in `out` array.
func put(_
byte: UInt8, _ out: inout [UInt8], _ outIndex: inout Int,
_ uncompressedSize: inout Int) {
@@ -289,7 +288,11 @@ public final class LZMA: DecompressionAlgorithm {
throw LZMAError.RangeDecoderError
}
var literalProbs = Array(repeating: Constants.probInitValue, count: 0x300 << (lc + lp).toInt())
/**
For literal decoding we need `1 << (lc + lp)` amount of tables.
Each table contains 0x300 probabilities.
*/
var literalProbs = Array(repeating: Array(repeating: Constants.probInitValue, count: 0x300), count: 1 << (lc + lp).toInt())
var isMatch = Array(repeating: Constants.probInitValue,
count: Constants.numStates << Constants.numPosBitsMax)
var isRep = Array(repeating: Constants.probInitValue, count: Constants.numStates)
@@ -328,17 +331,29 @@ public final class LZMA: DecompressionAlgorithm {
}
// DECODE LITERAL:
/// Previous literal (zero, if there was none).
let prevByte = outWindow.isEmpty ? 0 : outWindow.byte(at: 1)
// TODO: Something is not quite right.
/// Decoded symbol. Initial value is 1.
var symbol = 1
/**
Index of table with literal probabilities. It is based on the context which consists of:
- `lc` high bits of from previous literal. If there were none, i.e. it is the first literal, then this part is skipped.
- `lp` low bits from current position in output.
*/
let litState = ((outWindow.totalPosition & ((1 << lp.toInt()) - 1)) << lc.toInt()) + (prevByte >> (8 - lc)).toInt()
let probsIndex = 0x300 * litState
/// Selected table for literal decoding.
var probs = literalProbs[litState]
// If state is greater than 7 we need to do additional decoding with 'matchByte'.
if state >= 7 {
/**
Byte in output at position that is the `distance` bytes before current position,
where the `distance` is the distance from the latest decoded match.
*/
var matchByte = outWindow.byte(at: rep0 + 1)
repeat {
let matchBit = ((matchByte >> 7) & 1).toInt()
matchByte <<= 1
let bit = rangeDecoder.decode(bitWithProb: &literalProbs[((1 + matchBit) << 8) + symbol],
let bit = rangeDecoder.decode(bitWithProb: &probs[((1 + matchBit) << 8) + symbol],
pointerData: &pointerData)
symbol = (symbol << 1) | bit
if matchBit != bit {
@@ -347,12 +362,14 @@ public final class LZMA: DecompressionAlgorithm {
} while symbol < 0x100
}
while symbol < 0x100 {
symbol = (symbol << 1) | rangeDecoder.decode(bitWithProb: &literalProbs[symbol], pointerData: &pointerData)
symbol = (symbol << 1) | rangeDecoder.decode(bitWithProb: &probs[symbol], pointerData: &pointerData)
}
print(symbol)
let byte = (symbol - 0x100).toUInt8()
outWindow.put(byte, &out, &outIndex, &uncompressedSize)
// END.
// Finally, we need to update `state`.
if state < 4 {
state = 0
} else if (state < 10) {