59 lines
1.5 KiB
C
59 lines
1.5 KiB
C
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#pragma once
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#include <vector>
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namespace cgv {
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namespace math {
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/// permute array \c A with \c N values of type \c T according to permutation \c P such that \c A[i] moves to \c A[P[i]]
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template <typename T, typename I>
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void permute_array(size_t N, T* A, I* P) {
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for (size_t i = 0; i < N; ++i) {
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if (P[i] < 0) {
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// unmark permutation index
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P[i] = -P[i] - 1;
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continue;
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}
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T v = A[i];
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I j = P[i];
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while (j != i) {
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std::swap(A[j], v);
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I old_j = j;
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j = P[j];
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P[old_j] = -P[old_j] - 1;
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}
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A[i] = v;
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}
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}
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/// interface to permute function for arrays and permutations stored in vectors
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template <typename T, typename I>
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void permute_vector(std::vector<T>& V, std::vector<I>& P) {
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permute_array(V.size(), &V.front(), &P.front());
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}
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/// permute \c nr_rows rows of nested 2D array with \c nr_columns columns, step sizes to step by one row / column need to be provided
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template <typename T, typename I>
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void permute_arrays(T* data, I* P, size_t nr_rows, size_t nr_columns, size_t row_step, size_t column_step)
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{
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for (size_t y = 0; y < nr_columns; ++y) {
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for (size_t x = 0; x < nr_rows; ++x) {
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if (P[x] < 0) {
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P[x] = -P[x] - 1;
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continue;
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}
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T v = data[x*row_step + y*column_step];
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size_t j = P[x];
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while (j != x) {
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std::swap(data[j*row_step + y*column_step], v);
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size_t old_j = j;
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j = P[j];
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P[old_j] = -P[old_j] - 1;
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}
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data[x*row_step + y*column_step] = v;
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}
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}
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}
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}
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}
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