#include <stddef.h>
#include <stdint.h>

#include "sorters.h"

size_t binary_search(const char *needle, char *haystack, size_t nmel, size_t width, cmpfun cmp);

static void swap(char *a, char *b, size_t width)
{
#ifdef __GNUC__
	typedef uint32_t __attribute__((__may_alias__)) u32;

	if ((uintptr_t)a % 4 == 0 && (uintptr_t)b % 4 == 0) {
		for (; width >= 4; width -= 4) {
			uint32_t tmp = *((u32*)a);
			*((u32*)a) = *((u32*)b);
			*((u32*)b) = tmp;
			a += 4;
			b += 4;
		}
	}
#endif

	while (width--) {
		char tmp = *a;
		*a++ = *b;
		*b++ = tmp;
	}
}

/* rotates left */
static void rotate(char *base, size_t size, size_t shift)
{
	int dir = 1;
	while (shift) {
		while (2*shift <= size) {
			swap(base, base + dir*shift, shift);
			size -= shift;
			base += shift*dir;
		}
		shift = size - shift;
		base  = dir > 0 ? base + size - shift : base - shift;
		dir  *= -1;
	}
}

static void distribute_buffer(char *base, size_t bufnmel, size_t sortnmel, size_t width, cmpfun cmp)
{
	while (bufnmel && sortnmel) {
		char  *sorted    = base + bufnmel * width;
		size_t insertpos = binary_search(base, sorted, sortnmel, width, cmp);
		if (insertpos > 0) {
			rotate(base, (bufnmel + insertpos) * width, bufnmel * width);
		}

		base     += (insertpos + 1) * width;
		bufnmel  -= 1;
		sortnmel -= insertpos;
	}
}

#define MAX_SORTNET 8

static const uint8_t sortnet[][2] = {
	/* 0: index =  0 */
	/* 1: index =  0 */
	/* 2: index =  0 */
	{0,1},
	/* 3: index =  1 */
	{0,1}, {0,2}, {1,2},
	/* 4: index =  4 */
	{0,1}, {2,3}, {0,2}, {1,3}, {1,2},
	/* 5: index =  9 */
	{0,1}, {3,4}, {2,4}, {2,3}, {1,4}, {0,3}, {0,2}, {1,3}, {1,2},
	/* 6: index = 18 */
	{1,2}, {4,5}, {0,2}, {3,5}, {0,1}, {3,4}, {2,5}, {0,3}, {1,4}, {2,4},
	{1,3}, {2,3},
	/* 7: index = 30 */
	{1,2}, {3,4}, {5,6}, {0,2}, {3,5}, {4,6}, {0,1}, {4,5}, {2,6}, {0,4},
	{1,5}, {0,3}, {2,5}, {1,3}, {2,4}, {2,3},
	/* 8: index = 46 */
	{0,1}, {2,3}, {4,5}, {6,7}, {0,2}, {1,3}, {4,6}, {5,7}, {1,2}, {5,6},
	{0,4}, {3,7}, {1,5}, {2,6}, {1,4}, {3,6}, {2,4}, {3,5}, {3,4},
	/* 9: index = 65, if we used a sorting network this large */
};

static const uint8_t sortnet_index[] = { 0, 0, 0, 1, 4, 9, 18, 30, 46, 65 };

static void sorting_network(char *base, size_t nmel, size_t width, cmpfun cmp)
{
	for (int i = sortnet_index[nmel]; i < sortnet_index[nmel+1]; i++) {
		char *elem1 = base + sortnet[i][0] * width;
		char *elem2 = base + sortnet[i][1] * width;
		if (cmp(elem1, elem2) > 0) swap(elem1, elem2, width);
	}
}