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Add new procedure for huffman code length generation

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This commit is contained in:
Timofey Solomko
2017-09-17 13:02:09 +03:00
parent fd3a886893
commit e5d2b78781
2 changed files with 115 additions and 0 deletions
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SWCompression.xcodeproj/project.pbxproj
+10
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@@ -160,6 +160,10 @@
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0693DF531F2E499F00602300 /* test_empty_file.7z in Resources */ = {isa = PBXBuildFile; fileRef = 0693DF511F2E499F00602300 /* test_empty_file.7z */; };
0693DF551F2E4AEE00602300 /* test_empty_cont.7z in Resources */ = {isa = PBXBuildFile; fileRef = 0693DF541F2E4AEE00602300 /* test_empty_cont.7z */; };
06955E491F65C761004D5D79 /* BZip2+Lengths.swift in Sources */ = {isa = PBXBuildFile; fileRef = 06955E481F65C761004D5D79 /* BZip2+Lengths.swift */; };
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06991C701E05A9F70030FF07 /* test9.lzma in Resources */ = {isa = PBXBuildFile; fileRef = 06991C6D1E05A9F70030FF07 /* test9.lzma */; };
06991C711E05A9F70030FF07 /* test10.lzma in Resources */ = {isa = PBXBuildFile; fileRef = 06991C6E1E05A9F70030FF07 /* test10.lzma */; };
@@ -422,6 +426,7 @@
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0693DF511F2E499F00602300 /* test_empty_file.7z */ = {isa = PBXFileReference; lastKnownFileType = file; path = test_empty_file.7z; sourceTree = "<group>"; };
0693DF541F2E4AEE00602300 /* test_empty_cont.7z */ = {isa = PBXFileReference; lastKnownFileType = file; path = test_empty_cont.7z; sourceTree = "<group>"; };
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06991C6D1E05A9F70030FF07 /* test9.lzma */ = {isa = PBXFileReference; lastKnownFileType = file; path = test9.lzma; sourceTree = "<group>"; };
06991C6E1E05A9F70030FF07 /* test10.lzma */ = {isa = PBXFileReference; lastKnownFileType = file; path = test10.lzma; sourceTree = "<group>"; };
@@ -916,6 +921,7 @@
06FED40B1DD7717E0013DFB2 /* BZip2.swift */,
06CDFCA21F111D6C00292758 /* BZip2Error.swift */,
06D95AC01F4C54E0006B46AC /* BZip2Compression.swift */,
06955E481F65C761004D5D79 /* BZip2+Lengths.swift */,
0634D9821F5207C30002B675 /* SuffixArray.swift */,
06FEAD871F54B9AB00AD016E /* RecursiveHuffmanTree.swift */,
);
@@ -1241,6 +1247,7 @@
061C06531F0E904600832F0C /* ZipEndOfCentralDirectory.swift in Sources */,
06CDFCB81F111E6900292758 /* BitReader.swift in Sources */,
06BB8F311E0C2C720079FB9E /* LZMA2.swift in Sources */,
06955E4A1F65C761004D5D79 /* BZip2+Lengths.swift in Sources */,
065569691DC65C2A00A47E66 /* ZlibArchive.swift in Sources */,
061C064E1F0E901C00832F0C /* ZipLocalHeader.swift in Sources */,
063DF10E1DE1F07800F38082 /* Extensions.swift in Sources */,
@@ -1305,6 +1312,7 @@
061C06541F0E904600832F0C /* ZipEndOfCentralDirectory.swift in Sources */,
06CDFCB91F111E6900292758 /* BitReader.swift in Sources */,
06BB8F321E0C2C720079FB9E /* LZMA2.swift in Sources */,
06955E4B1F65C761004D5D79 /* BZip2+Lengths.swift in Sources */,
063DF1191DE1F2E200F38082 /* DataWithPointer.swift in Sources */,
061C064F1F0E901C00832F0C /* ZipLocalHeader.swift in Sources */,
063DF11A1DE1F2E200F38082 /* Extensions.swift in Sources */,
@@ -1369,6 +1377,7 @@
061C06551F0E904600832F0C /* ZipEndOfCentralDirectory.swift in Sources */,
06CDFCBA1F111E6900292758 /* BitReader.swift in Sources */,
06BB8F331E0C2C720079FB9E /* LZMA2.swift in Sources */,
06955E4C1F65C761004D5D79 /* BZip2+Lengths.swift in Sources */,
065569771DC65C2B00A47E66 /* ZlibArchive.swift in Sources */,
061C06501F0E901C00832F0C /* ZipLocalHeader.swift in Sources */,
063DF10F1DE1F07800F38082 /* Extensions.swift in Sources */,
@@ -1433,6 +1442,7 @@
061C06521F0E904600832F0C /* ZipEndOfCentralDirectory.swift in Sources */,
06CDFCB71F111E6900292758 /* BitReader.swift in Sources */,
06BB8F301E0C2C720079FB9E /* LZMA2.swift in Sources */,
06955E491F65C761004D5D79 /* BZip2+Lengths.swift in Sources */,
06A393391DE0709300182E12 /* GzipArchive.swift in Sources */,
061C064D1F0E901C00832F0C /* ZipLocalHeader.swift in Sources */,
063DF10D1DE1F07800F38082 /* Extensions.swift in Sources */,
Sources/BZip2+Lengths.swift
+105
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@@ -0,0 +1,105 @@
// Copyright (c) 2017 Timofey Solomko
// Licensed under MIT License
//
// See LICENSE for license information
import Foundation
// BZip2 specific function for generation of HuffmanLength array from stats.
extension BZip2 {
/**
Based on "procedure for generating the lists which specify a Huffman code table" (annexes C and K)
from Recommendation T.81 of ITU (aka JPEG specfications).
*/
static func lengths(from stats: [Int]) -> [HuffmanLength] {
if stats.count == 0 {
return []
} else if stats.count == 1 {
return [HuffmanLength(symbol: 0, codeLength: 1)]
}
/// Mutable copy of input `stats`.
var stats = stats
var codeSizes = Array(repeating: 0, count: 259)
var others = Array(repeating: -1, count: 259)
while true {
var c1 = -1
var minFreq = Int.max
for i in 0..<stats.count {
if stats[i] > 0 && stats[i] <= minFreq {
minFreq = stats[i]
c1 = i
}
}
var c2 = -1
minFreq = Int.max
for i in 0..<stats.count {
if stats[i] > 0 && stats[i] <= minFreq && i != c1 {
minFreq = stats[i]
c2 = i
}
}
guard c2 >= 0
else { break }
stats[c1] += stats[c2]
stats[c2] = 0
codeSizes[c1] += 1
while others[c1] >= 0 {
c1 = others[c1]
codeSizes[c1] += 1
}
others[c1] = c2
codeSizes[c2] += 1
while others[c2] >= 0 {
c2 = others[c2]
codeSizes[c2] += 1
}
}
// Now we count code lengths.
// In worst case scenario the maximum code length is 258.
var bits = Array(repeating: 0, count: 259)
for i in 0..<bits.count {
// We don't check for zero code length because we have unused element in `bits` array for them.
bits[codeSizes[i]] += 1
}
// Adjust_bits
for i in stride(from: 258, to: 20, by: -1) {
while bits[i] > 0 {
var j = i - 2
while bits[j] == 0 {
j -= 1
}
bits[i] -= 2
bits[i - 1] += 1
bits[j + 1] += 2
bits[j] -= 1
}
}
// Generate_size_table
var symbol = 0
var lengths = [HuffmanLength]()
for i in 1...20 {
var j = 1
while j <= bits[i] {
lengths.append(HuffmanLength(symbol: symbol, codeLength: i))
symbol += 1
j += 1
}
}
return lengths
}
}