img2col function for pointers to floats in swift

main.swift
func img2col(_ input: UnsafePointer<Float>, _ channels: Int, _ height: Int, _ width: Int, _ kernelSize: Int, _ stride: Int, _ padding: Int) -> [Float] {
    let outputHeight = (height + 2 * padding - kernelSize) / stride + 1
    let outputWidth = (width + 2 * padding - kernelSize) / stride + 1

    var colData = [Float](repeatElement(0, count: kernelSize * kernelSize * channels * outputHeight * outputWidth))

    for c in 0..<channels {
        for y in 0..<kernelSize {
            for x in 0..<kernelSize {
                var dstIndex = c * (kernelSize * kernelSize * outputHeight * outputWidth) + y * (kernelSize * outputHeight * outputWidth) + x * (outputHeight * outputWidth)

                for j in 0..<outputHeight {
                    for i in 0..<outputWidth {
                        var srcIndexY = y + j * stride - padding
                        var srcIndexX = x + i * stride - padding
                        if (srcIndexY >= 0 && srcIndexY < height && srcIndexX >= 0 && srcIndexX < width) {
                            var srcIndex = (c * height + srcIndexY) * width + srcIndexX
                            colData[dstIndex] = input[srcIndex]
                        }

                        dstIndex += 1
                    }
                }
            }
        }
    }

    return colData
}
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