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node_modules/expo-image/ios/Utils/Blurhash.swift

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+// The blurhash algorithm was entirely created by Wolt Enterprises.
+// This implementation was inspired by:
+// - https://github.com/woltapp/blurhash/blob/master/Swift/BlurHashDecode.swift
+// - https://github.com/woltapp/blurhash/blob/master/Swift/BlurHashEncode.swift
+// See https://blurha.sh for more details about the blurhash.
+
+import UIKit
+
+// swiftlint:disable force_unwrapping
+
+internal func image(fromBlurhash blurhash: String, size: CGSize, punch: Float = 1.0) -> CGImage? {
+  guard blurhash.count >= 6 else {
+    return nil
+  }
+
+  let sizeFlag = decode83(String(blurhash[0]))
+  let numY = (sizeFlag / 9) + 1
+  let numX = (sizeFlag % 9) + 1
+
+  let quantisedMaximumValue = decode83(String(blurhash[1]))
+  let maximumValue = Float(quantisedMaximumValue + 1) / 166
+
+  guard blurhash.count == 4 + 2 * numX * numY else {
+    return nil
+  }
+
+  let colors: [(Float, Float, Float)] = (0 ..< numX * numY).map { i in
+    if i == 0 {
+      let value = decode83(String(blurhash[2 ..< 6]))
+      return decodeDC(value)
+    } else {
+      let value = decode83(String(blurhash[4 + i * 2 ..< 4 + i * 2 + 2]))
+      return decodeAC(value, maximumValue: maximumValue * punch)
+    }
+  }
+
+  let width = Int(size.width)
+  let height = Int(size.height)
+  let bytesPerRow = width * 3
+
+  guard let data = CFDataCreateMutable(kCFAllocatorDefault, bytesPerRow * height) else {
+    return nil
+  }
+
+  CFDataSetLength(data, bytesPerRow * height)
+
+  guard let pixels = CFDataGetMutableBytePtr(data) else {
+    return nil
+  }
+
+  for y in 0 ..< height {
+    for x in 0 ..< width {
+      var r: Float = 0
+      var g: Float = 0
+      var b: 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 color = colors[i + j * numX]
+          r += color.0 * basis
+          g += color.1 * basis
+          b += color.2 * basis
+        }
+      }
+
+      let intR = UInt8(linearTosRGB(r))
+      let intG = UInt8(linearTosRGB(g))
+      let intB = UInt8(linearTosRGB(b))
+
+      pixels[3 * x + 0 + y * bytesPerRow] = intR
+      pixels[3 * x + 1 + y * bytesPerRow] = intG
+      pixels[3 * x + 2 + y * bytesPerRow] = intB
+    }
+  }
+
+  let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)
+
+  guard let provider = CGDataProvider(data: data), 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
+  }
+
+  return cgImage
+}
+
+internal func blurhash(fromImage image: UIImage, numberOfComponents components: (Int, Int)) -> String? {
+  let size = image.size
+  let scale = image.scale
+
+  let pixelWidth = Int(round(size.width * scale))
+  let pixelHeight = Int(round(size.height * scale))
+
+  let context = CGContext(
+    data: nil,
+    width: pixelWidth,
+    height: pixelHeight,
+    bitsPerComponent: 8,
+    bytesPerRow: pixelWidth * 4,
+    space: CGColorSpace(name: CGColorSpace.sRGB)!,
+    bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
+  )!
+  context.scaleBy(x: scale, y: -scale)
+  context.translateBy(x: 0, y: -size.height)
+
+  UIGraphicsPushContext(context)
+  image.draw(at: .zero)
+  UIGraphicsPopContext()
+
+  guard let cgImage = context.makeImage(),
+    let dataProvider = cgImage.dataProvider,
+    let data = dataProvider.data,
+    let pixels = CFDataGetBytePtr(data) else {
+    assertionFailure("Unexpected error!")
+    return nil
+  }
+
+  let width = cgImage.width
+  let height = cgImage.height
+  let bytesPerRow = cgImage.bytesPerRow
+
+  var factors: [(Float, Float, Float)] = []
+  for y in 0 ..< components.1 {
+    for x in 0 ..< components.0 {
+      let normalisation: Float = (x == 0 && y == 0) ? 1 : 2
+      let factor = multiplyBasisFunction(
+        pixels: pixels,
+        width: width,
+        height: height,
+        bytesPerRow: bytesPerRow,
+        bytesPerPixel: cgImage.bitsPerPixel / 8,
+        pixelOffset: 0
+      ) {
+        normalisation * cos(Float.pi * Float(x) * $0 / Float(width)) as Float * cos(Float.pi * Float(y) * $1 / Float(height)) as Float
+      }
+      factors.append(factor)
+    }
+  }
+
+  let dc = factors.first!
+  let ac = factors.dropFirst()
+
+  var hash = ""
+
+  let sizeFlag = (components.0 - 1) + (components.1 - 1) * 9
+  hash += encode83(sizeFlag, length: 1)
+
+  let maximumValue: Float
+  if !ac.isEmpty {
+    let actualMaximumValue = ac.map({ max(abs($0.0), abs($0.1), abs($0.2)) }).max()!
+    let quantisedMaximumValue = Int(max(0, min(82, floor(actualMaximumValue * 166 - 0.5))))
+    maximumValue = Float(quantisedMaximumValue + 1) / 166
+    hash += encode83(quantisedMaximumValue, length: 1)
+  } else {
+    maximumValue = 1
+    hash += encode83(0, length: 1)
+  }
+
+  hash += encode83(encodeDC(dc), length: 4)
+
+  for factor in ac {
+    hash += encode83(encodeAC(factor, maximumValue: maximumValue), length: 2)
+  }
+
+  return hash
+}
+
+internal func isBlurhash(_ str: String) -> Bool {
+  return str.allSatisfy { char in decodeCharacters[char] != nil }
+}
+
+// MARK: - Encode
+
+// swiftlint:disable:next function_parameter_count
+private func multiplyBasisFunction(
+  pixels: UnsafePointer<UInt8>,
+  width: Int,
+  height: Int,
+  bytesPerRow: Int,
+  bytesPerPixel: Int,
+  pixelOffset: Int,
+  basisFunction: (Float, Float) -> Float
+) -> (Float, Float, Float) {
+  var r: Float = 0
+  var g: Float = 0
+  var b: Float = 0
+
+  let buffer = UnsafeBufferPointer(start: pixels, count: height * bytesPerRow)
+
+  for x in 0 ..< width {
+    for y in 0 ..< height {
+      let basis = basisFunction(Float(x), Float(y))
+      r += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 0 + y * bytesPerRow])
+      g += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 1 + y * bytesPerRow])
+      b += basis * sRGBToLinear(buffer[bytesPerPixel * x + pixelOffset + 2 + y * bytesPerRow])
+    }
+  }
+
+  let scale = 1 / Float(width * height)
+
+  return (r * scale, g * scale, b * scale)
+}
+
+private let encodeCharacters: [Character] = Array("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~")
+
+private func encodeDC(_ value: (Float, Float, Float)) -> Int {
+  let roundedR = linearTosRGB(value.0)
+  let roundedG = linearTosRGB(value.1)
+  let roundedB = linearTosRGB(value.2)
+  return (roundedR << 16) + (roundedG << 8) + roundedB
+}
+
+private func encodeAC(_ value: (Float, Float, Float), maximumValue: Float) -> Int {
+  let quantR = Int(max(0, min(18, floor(signPow(value.0 / maximumValue, 0.5) * 9 + 9.5))))
+  let quantG = Int(max(0, min(18, floor(signPow(value.1 / maximumValue, 0.5) * 9 + 9.5))))
+  let quantB = Int(max(0, min(18, floor(signPow(value.2 / maximumValue, 0.5) * 9 + 9.5))))
+
+  return quantR * 19 * 19 + quantG * 19 + quantB
+}
+
+private func encode83(_ value: Int, length: Int) -> String {
+  var result = ""
+  for i in 1 ... length {
+    let digit = (value / pow(83, length - i)) % 83
+    result += String(encodeCharacters[Int(digit)])
+  }
+  return result
+}
+
+// MARK: - Decode
+
+private func decodeDC(_ value: Int) -> (Float, Float, Float) {
+  let intR = value >> 16
+  let intG = (value >> 8) & 255
+  let intB = value & 255
+  return (sRGBToLinear(intR), sRGBToLinear(intG), sRGBToLinear(intB))
+}
+
+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 rgb = (
+    signPow((Float(quantR) - 9) / 9, 2) * maximumValue,
+    signPow((Float(quantG) - 9) / 9, 2) * maximumValue,
+    signPow((Float(quantB) - 9) / 9, 2) * maximumValue
+  )
+
+  return rgb
+}
+
+private let decodeCharacters: [Character: Int] = {
+  var dict: [Character: Int] = [:]
+  for (index, character) in encodeCharacters.enumerated() {
+    dict[character] = index
+  }
+  return dict
+}()
+
+private func decode83(_ str: String) -> Int {
+  var value: Int = 0
+  for character in str {
+    if let digit = decodeCharacters[character] {
+      value = value * 83 + digit
+    }
+  }
+  return value
+}
+
+// MARK: - Helpers
+
+private func signPow(_ value: Float, _ exp: Float) -> Float {
+  return copysign(pow(abs(value), exp), value)
+}
+
+private func linearTosRGB(_ value: Float) -> Int {
+  let v = max(0, min(1, value))
+  if v <= 0.0031308 {
+    return Int(v * 12.92 * 255 + 0.5)
+  } else {
+    return Int((1.055 * pow(v, 1 / 2.4) - 0.055) * 255 + 0.5)
+  }
+}
+
+private func sRGBToLinear<Type: BinaryInteger>(_ value: Type) -> Float {
+  let v = Float(Int64(value)) / 255
+  if v <= 0.04045 {
+    return v / 12.92
+  } else {
+    return pow((v + 0.055) / 1.055, 2.4)
+  }
+}
+
+private func pow(_ base: Int, _ exponent: Int) -> Int {
+  return (0 ..< exponent).reduce(1) { value, _ in value * base }
+}
+
+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]
+  }
+}