72 lines
1.9 KiB
C
72 lines
1.9 KiB
C
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#ifndef INCLUDED_C_SHELLSORT_H
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#define INCLUDED_C_SHELLSORT_H
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#ifndef INCLUDED_C_TYPES_H
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#include <c_Types.h>
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#endif /*INCLUDED_C_TYPES_H*/
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#ifndef INCLUDED_C_MEMORY_H
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#include <c_Memory.h>
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#endif /*INCLUDED_C_MEMORY_H*/
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/* ------------------------------------------------------------------------------------------------------------------ */
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/* */
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C_STATIC_FORCE_INLINE
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void c_ShellSort(void* base, c_size_t num, c_size_t size,
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int (*compar)(const void*, const void*)) {
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if (base == NULL || num < 2 || size == 0) return;
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char* arr = (char*)base;
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// Stack optimization for memory swap space
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#define STACK_LIMIT 128
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char stack_buf[STACK_LIMIT];
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void* temp = NULL;
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if (size <= STACK_LIMIT) {
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temp = stack_buf;
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} else {
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temp = C_ALLOC(size);
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if (temp == NULL) return;
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}
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// Using Knuth's gap sequence: h = h * 3 + 1 (1, 4, 13, 40, 121, ...)
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c_size_t gap = 1;
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while (gap < num / 3) {
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gap = gap * 3 + 1;
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}
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// Start with the largest gap and work down to a gap of 1
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while (gap > 0) {
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for (c_size_t i = gap; i < num; i++) {
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// temp = arr[i]
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memcpy(temp, arr + (i * size), size);
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c_size_t j = i;
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// Shift elements of the gap-sorted variant until the correct position is found
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// Loop guards prevent underflow on unsigned c_size_t subtraction (j >= gap)
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while (j >= gap && compar(arr + ((j - gap) * size), temp) > 0) {
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// arr[j] = arr[j - gap]
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memcpy(arr + (j * size), arr + ((j - gap) * size), size);
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j -= gap;
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}
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// arr[j] = temp
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memcpy(arr + (j * size), temp, size);
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}
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// Reduce the gap
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gap /= 3;
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}
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if (size > STACK_LIMIT) {
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C_FREE(temp);
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}
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#undef STACK_LIMIT
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}
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#endif /*INCLUDED_C_SHELLSORT_H*/
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