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#include <math.h>
#include <stddef.h>
#include <stdint.h>
#include "sorters.h"
#include "common.h"
#define TAIL(base,nmel,width) ((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 *base, size_t anmel, size_t bnmel, size_t bufnmel, size_t width, cmpfun cmp)
{
char *a_end = base + anmel * width;
char *b_end = a_end + bnmel * width;
char *buf_end = b_end + bufnmel * width;
size_t count = 0;
while (bnmel) {
char *a = a_end - width;
char *b = b_end - width;
char *buf = buf_end - width;
if (cmp(a, b) > 0) { swap(a, buf, width); a_end = a; anmel--; }
else { swap(b, buf, width); b_end = b; bnmel--; }
count++;
buf_end = buf;
}
return count;
}
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;
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 bufidx = blocks * blknmel;
while (blocks > 1) {
size_t overlap = last_overlap(base, blocks, bwidth, width, cmp);
if (overlap) {
bufidx -= merge(TAIL(base, overlap, bwidth), blknmel, bufidx - overlap*blknmel, bufnmel, width, cmp);
}
blocks = overlap;
}
if (bufidx) {
rotate(base, (bufidx + bufnmel) * width, bufidx * width);
}
distribute:
grailsort(base, bufnmel, width, cmp);
distribute_buffer(base, bufnmel, nmel - bufnmel, width, cmp);
}
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