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Improved performance of swift decode by 2-4x by caching cos operations #80

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Improved performance of swift decode by 2-4x by caching cos operations #80

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136 changes: 80 additions & 56 deletions Swift/BlurHashDecode.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -4,18 +4,18 @@ extension UIImage {
public convenience init?(blurHash: String, size: CGSize, punch: Float = 1) {
guard blurHash.count >= 6 else { return nil }

let sizeFlag = String(blurHash[0]).decode83()
let numY = (sizeFlag / 9) + 1
let numX = (sizeFlag % 9) + 1
let sizeFlag = String(blurHash[0]).decode83()
let numY = (sizeFlag / 9) + 1
let numX = (sizeFlag % 9) + 1

let quantisedMaximumValue = String(blurHash[1]).decode83()
let quantisedMaximumValue = String(blurHash[1]).decode83()
let maximumValue = Float(quantisedMaximumValue + 1) / 166

guard blurHash.count == 4 + 2 * numX * numY else { return nil }

let colours: [(Float, Float, Float)] = (0 ..< numX * numY).map { i in
if i == 0 {
let value = String(blurHash[2 ..< 6]).decode83()
let value = String(blurHash[2 ..< 6]).decode83()
return decodeDC(value)
} else {
let value = String(blurHash[4 + i * 2 ..< 4 + i * 2 + 2]).decode83()
Expand All @@ -30,25 +30,40 @@ extension UIImage {
CFDataSetLength(data, bytesPerRow * height)
guard let pixels = CFDataGetMutableBytePtr(data) else { return nil }

let cosxi = (0 ..< width).map { x in
(0 ..< numX).map { i in
cos(Float.pi * Float(x) * Float(i) / Float(width))
}
}

let cosyj = (0 ..< height).map { y in
(0 ..< numY).map { j in
cos(Float.pi * Float(y) * Float(j) / Float(height))
}
}

for y in 0 ..< height {
let cosj = cosyj[y]
for x in 0 ..< width {
var r: Float = 0
var g: Float = 0
var b: Float = 0
let cosi = cosxi[x]

var red: Float = 0
var green: Float = 0
var blue: Float = 0

for j in 0 ..< numY {
for i in 0 ..< numX {
let basis = cos(Float.pi * Float(x) * Float(i) / Float(width)) * cos(Float.pi * Float(y) * Float(j) / Float(height))
let basis = cosi[i] * cosj[j]
let colour = colours[i + j * numX]
r += colour.0 * basis
g += colour.1 * basis
b += colour.2 * basis
red += colour.0 * basis
green += colour.1 * basis
blue += colour.2 * basis
}
}

let intR = UInt8(linearTosRGB(r))
let intG = UInt8(linearTosRGB(g))
let intB = UInt8(linearTosRGB(b))
let intR = UInt8(linearTosRGB(red))
let intG = UInt8(linearTosRGB(green))
let intB = UInt8(linearTosRGB(blue))

pixels[3 * x + 0 + y * bytesPerRow] = intR
pixels[3 * x + 1 + y * bytesPerRow] = intG
Expand All @@ -59,8 +74,17 @@ extension UIImage {
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)

guard let provider = CGDataProvider(data: data) else { return nil }
guard let cgImage = CGImage(width: width, height: height, bitsPerComponent: 8, bitsPerPixel: 24, bytesPerRow: bytesPerRow,
space: CGColorSpaceCreateDeviceRGB(), bitmapInfo: bitmapInfo, provider: provider, decode: nil, shouldInterpolate: true, intent: .defaultIntent) else { return nil }
guard let cgImage = CGImage(width: width,
height: height,
bitsPerComponent: 8,
bitsPerPixel: 24,
bytesPerRow: bytesPerRow,
space: CGColorSpaceCreateDeviceRGB(),
bitmapInfo: bitmapInfo,
provider: provider,
decode: nil,
shouldInterpolate: true,
intent: .defaultIntent) else { return nil }

self.init(cgImage: cgImage)
}
Expand All @@ -74,17 +98,17 @@ private func decodeDC(_ value: Int) -> (Float, Float, Float) {
}

private func decodeAC(_ value: Int, maximumValue: Float) -> (Float, Float, Float) {
let quantR = value / (19 * 19)
let quantG = (value / 19) % 19
let quantB = value % 19
let quantR = value / (19 * 19)
let quantG = (value / 19) % 19
let quantB = value % 19

let rgb = (
signPow((Float(quantR) - 9) / 9, 2) * maximumValue,
signPow((Float(quantG) - 9) / 9, 2) * maximumValue,
signPow((Float(quantB) - 9) / 9, 2) * maximumValue
)
let rgb = (
signPow((Float(quantR) - 9) / 9, 2) * maximumValue,
signPow((Float(quantG) - 9) / 9, 2) * maximumValue,
signPow((Float(quantB) - 9) / 9, 2) * maximumValue
)

return rgb
return rgb
}

private func signPow(_ value: Float, _ exp: Float) -> Float {
Expand All @@ -104,43 +128,43 @@ private func sRGBToLinear<Type: BinaryInteger>(_ value: Type) -> Float {
}

private let encodeCharacters: [String] = {
return "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~".map { String($0) }
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~".map { String($0) }
}()

private let decodeCharacters: [String: Int] = {
var dict: [String: Int] = [:]
for (index, character) in encodeCharacters.enumerated() {
dict[character] = index
}
return dict
var dict: [String: Int] = [:]
for (index, character) in encodeCharacters.enumerated() {
dict[character] = index
}
return dict
}()

extension String {
func decode83() -> Int {
var value: Int = 0
for character in self {
if let digit = decodeCharacters[String(character)] {
value = value * 83 + digit
}
}
return value
}
func decode83() -> Int {
var value: Int = 0
for character in self {
if let digit = decodeCharacters[String(character)] {
value = value * 83 + digit
}
}
return value
}
}

private extension String {
subscript (offset: Int) -> Character {
return self[index(startIndex, offsetBy: offset)]
}

subscript (bounds: CountableClosedRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start...end]
}

subscript (bounds: CountableRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start..<end]
}
subscript(offset: Int) -> Character {
return self[index(startIndex, offsetBy: offset)]
}

subscript(bounds: CountableClosedRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ... end]
}

subscript(bounds: CountableRange<Int>) -> Substring {
let start = index(startIndex, offsetBy: bounds.lowerBound)
let end = index(startIndex, offsetBy: bounds.upperBound)
return self[start ..< end]
}
}