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ExtraLength and extraDistance calculations are now done inside decompress function.

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This commit is contained in:
Timofey Solomko
2016-11-01 23:49:26 +03:00
parent 9f6de9fce4
commit 9e88447bb6
2 changed files with 6 additions and 27 deletions
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Sources/Deflate.swift
+5 -6
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@@ -169,10 +169,10 @@ public class Deflate: DecompressionAlgorithm {
break
} else if symbol >= 257 && symbol <= 285 {
let start = (index, shift)
let addBits = HuffmanTable.Constants.extraLengthBits(n: symbol)
guard addBits != -1 else { throw DeflateError.HuffmanTableError }
index += shift + addBits >= 8 ? 1 : 0
shift = shift + addBits >= 8 ? shift - (8 - addBits) : shift + addBits
let extraLength = (257 <= symbol && symbol <= 260) || symbol == 285 ?
0 : ((symbol - 257) >> 2) - 1
index += shift + extraLength >= 8 ? 1 : 0
shift = shift + extraLength >= 8 ? shift - (8 - extraLength) : shift + extraLength
let end = (index, shift)
var length = HuffmanTable.Constants.lengthBase[symbol - 257] +
convertToInt(reversedUint8Array: data.bits(from: start, to: end))
@@ -186,8 +186,7 @@ public class Deflate: DecompressionAlgorithm {
if newSymbol >= 0 && newSymbol <= 29 {
let start = (index, shift)
let extraDistance = HuffmanTable.Constants.extraDistanceBits(n: newSymbol)
guard extraDistance != -1 else { throw DeflateError.HuffmanTableError }
let extraDistance = newSymbol == 0 || newSymbol == 1 ? 0 : (newSymbol >> 1) - 1
if shift + extraDistance >= 16 {
index += 2
shift = shift - (16 - extraDistance)
Sources/HuffmanTable.swift
+1 -21
View File
@@ -14,7 +14,7 @@ class HuffmanTable: CustomStringConvertible {
static let codeLengthOrders: [Int] =
[16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15]
// Substract 257 from index!
/// - Warning: Substract 257 from index!
static let lengthBase: [Int] =
[3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35,
43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258]
@@ -24,26 +24,6 @@ class HuffmanTable: CustomStringConvertible {
257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145,
8193, 12289, 16385, 24577]
static func extraLengthBits(n: Int) -> Int {
if (n >= 257 && n <= 260) || n == 285 {
return 0
} else if n >= 261 && n <= 284 {
return ((n - 257) >> 2) - 1
} else {
return -1
}
}
static func extraDistanceBits(n: Int) -> Int {
if n >= 0 && n <= 1 {
return 0
} else if n >= 2 && n <= 29 {
return (n >> 1) - 1
} else {
return -1
}
}
}
var lengths: [HuffmanLength]