79 lines
1.7 KiB
Go
79 lines
1.7 KiB
Go
// Copyright 2017 The goimagehash Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package etcs
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import "golang.org/x/exp/constraints"
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type Number interface {
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constraints.Integer | constraints.Float
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}
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// MeanOfPixels function returns a mean of pixels.
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func MeanOfPixels[N Number](pixels []N) N {
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var m float64 = 0
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lens := float64(len(pixels))
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if lens == 0 {
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return 0
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}
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for _, p := range pixels {
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m += float64(p)
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}
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// print(m," ", lens, "\n")
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return N(m / lens)
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}
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// MedianOfPixels function returns a median value of pixels.
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// It uses quick selection algorithm.
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func MedianOfPixels[N Number](pixels []N) N {
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tmp := make([]N, len(pixels))
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copy(tmp, pixels)
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l := len(tmp)
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pos := l / 2
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v := quickSelectMedian(tmp, 0, l-1, pos)
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return v
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}
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// MedianOfPixelsFast64 function returns a median value of pixels.
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// It uses quick selection algorithm.
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func MedianOfPixelsFast64[N Number](pixels []N) N {
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tmp := [64]N{}
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copy(tmp[:], pixels)
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l := len(tmp)
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pos := l / 2
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return quickSelectMedian(tmp[:], 0, l-1, pos)
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}
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func quickSelectMedian[N Number](sequence []N, low, hi, k int) N {
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if low == hi {
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return sequence[k]
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}
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for low < hi {
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pivot := low/2 + hi/2
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pivotValue := sequence[pivot]
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storeIdx := low
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sequence[pivot], sequence[hi] = sequence[hi], sequence[pivot]
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for i := low; i < hi; i++ {
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if sequence[i] < pivotValue {
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sequence[storeIdx], sequence[i] = sequence[i], sequence[storeIdx]
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storeIdx++
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}
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}
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sequence[hi], sequence[storeIdx] = sequence[storeIdx], sequence[hi]
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if k <= storeIdx {
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hi = storeIdx
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} else {
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low = storeIdx + 1
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}
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}
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if len(sequence)%2 == 0 {
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return sequence[k-1]/2 + sequence[k]/2
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}
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return sequence[k]
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}
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