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#include <math.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <limits.h>
#include "sorters.h"
#include "common.h"
static inline void *tail(char *base, size_t nmel, size_t width)
{
return base + (nmel-1) * width;
}
/* get index of last block whose head is less than the previous block's tail */
static size_t last_overlap(char *base, size_t bcount, size_t bwidth, size_t width, cmpfun cmp)
{
for (char *cur = tail(base, bcount, bwidth); --bcount; cur -= bwidth)
if (cmp(cur - width, cur) > 0) break;
return bcount;
}
size_t merge(char *buf, char *a, char *b, size_t bufnmel, size_t anmel, size_t bnmel, size_t width, cmpfun cmp)
{
while (bnmel) {
char *a_tail = tail(a, anmel, width);
char *b_tail = tail(b, bnmel, width);
char *buf_tail = tail(buf, bufnmel, width);
if (cmp(a_tail, b_tail) <= 0) {
swap(buf_tail, b_tail, width);
bnmel--;
} else {
swap(buf_tail, a_tail, width);
anmel--;
}
bufnmel--;
}
return anmel;
}
void grailsort(void *unsorted, size_t nmel, size_t width, cmpfun cmp)
{
char *base = unsorted;
if (nmel <= MAX_SORTNET) {
sorting_network(base, nmel, width, cmp);
return;
}
size_t blknmel = sqrt(nmel); /* elements in a block */
size_t bufnmel = blknmel + nmel % blknmel; /* elements in the buffer */
size_t bwidth = blknmel * width; /* size of a block in bytes */
size_t blocks = nmel / blknmel - 1; /* number of blocks in a + b */
size_t acount = blocks / 2;
size_t bcount = blocks - acount;
char *a = base;
char *b = a + acount * bwidth;
char *buf = b + bcount * bwidth;
grailsort(a, acount * blknmel, width, cmp);
grailsort(b, bcount * blknmel, width, cmp);
/* sort all the a and b blocks together by their head elements */
grailsort(base, blocks, bwidth, cmp);
/* merge, starting from the end and working towards the beginning */
size_t last_nmel = blknmel;
while (blocks > 1) {
size_t overlap = last_overlap(base, blocks, bwidth, width, cmp);
if (!overlap) break;
char *block_a = base + bwidth * (overlap-1);
char *block_b = base + bwidth * overlap;
size_t bnmel = (blocks - overlap - 1) * blknmel + last_nmel;
last_nmel = merge(buf, block_a, block_b, bufnmel, blknmel, bnmel, width, cmp);
buf = block_a + last_nmel * width;
blocks = overlap;
}
rotate(base, buf-base + bufnmel*width, buf-base);
grailsort(base, bufnmel, width, cmp);
distribute_buffer(base, bufnmel, nmel - bufnmel, width, cmp);
}
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