/*-*- mode:c;indent-tabs-mode:t;c-basic-offset:8;tab-width:8;coding:utf-8 -*-│
│vi: set et ft=c ts=8 tw=8 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright (c) 1991, 1993 │
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╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/mem/alg.h"
#include "libc/mem/mem.h"
#include "libc/sysv/errfuns.h"
// clang-format off
/*
* Swap two areas of size number of bytes. Although qsort(3) permits random
* blocks of memory to be sorted, sorting pointers is almost certainly the
* common case (and, were it not, could easily be made so). Regardless, it
* isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
* arithmetic gets lost in the time required for comparison function calls.
*/
#define SWAP(a, b, count, size, tmp) { \
count = size; \
do { \
tmp = *a; \
*a++ = *b; \
*b++ = tmp; \
} while (--count); \
}
/* Copy one block of size size to another. */
#define COPY(a, b, count, size, tmp1, tmp2) { \
count = size; \
tmp1 = a; \
tmp2 = b; \
do { \
*tmp1++ = *tmp2++; \
} while (--count); \
}
/*
* Build the list into a heap, where a heap is defined such that for
* the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
*
* There are two cases. If j == nmemb, select largest of Ki and Kj. If
* j < nmemb, select largest of Ki, Kj and Kj+1.
*/
#define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
par_i = child_i) { \
child = base + child_i * size; \
if (child_i < nmemb && compar(child, child + size, z) < 0) { \
child += size; \
++child_i; \
} \
par = base + par_i * size; \
if (compar(child, par, z) <= 0) \
break; \
SWAP(par, child, count, size, tmp); \
} \
}
/*
* Select the top of the heap and 'heapify'. Since by far the most expensive
* action is the call to the compar function, a considerable optimization
* in the average case can be achieved due to the fact that k, the displaced
* element, is usually quite small, so it would be preferable to first
* heapify, always maintaining the invariant that the larger child is copied
* over its parent's record.
*
* Then, starting from the *bottom* of the heap, finding k's correct place,
* again maintaining the invariant. As a result of the invariant no element
* is 'lost' when k is assigned its correct place in the heap.
*
* The time savings from this optimization are on the order of 15-20% for the
* average case. See Knuth, Vol. 3, page 158, problem 18.
*
* XXX Don't break the #define SELECT line, below. Reiser cpp gets upset.
*/
#define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
child = base + child_i * size; \
if (child_i < nmemb && compar(child, child + size, z) < 0) { \
child += size; \
++child_i; \
} \
par = base + par_i * size; \
COPY(par, child, count, size, tmp1, tmp2); \
} \
for (;;) { \
child_i = par_i; \
par_i = child_i / 2; \
child = base + child_i * size; \
par = base + par_i * size; \
if (child_i == 1 || compar(k, par, z) < 0) { \
COPY(child, k, count, size, tmp1, tmp2); \
break; \
} \
COPY(child, par, count, size, tmp1, tmp2); \
} \
}
/**
* Sorts array w/ optional callback argument.
*
* @param vbase is base of array
* @param nmemb is item count
* @param size is item width
* @param compar is a callback returning <0, 0, or >0
* @param z will optionally be passed as the third argument to cmp
* @see heapsort()
*/
int
heapsort_r(void *vbase, size_t nmemb, size_t size,
int (*compar)(const void *, const void *, void *), void *z)
{
size_t cnt, i, j, l;
char tmp, *tmp1, *tmp2;
char *base, *k, *p, *t;
if (nmemb <= 1)
return (0);
if (!size)
return (einval());
if ((k = malloc(size)) == NULL)
return (-1);
/*
* Items are numbered from 1 to nmemb, so offset from size bytes
* below the starting address.
*/
base = (char *)vbase - size;
for (l = nmemb / 2 + 1; --l;)
CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
/*
* For each element of the heap, save the largest element into its
* final slot, save the displaced element (k), then recreate the
* heap.
*/
while (nmemb > 1) {
COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
--nmemb;
SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
}
free(k);
return (0);
}
/**
* Sorts array.
*
* Runs in O (N lg N), both average and worst. While heapsort is faster
* than the worst case of quicksort, the BSD quicksort does median
* selection so that the chance of finding a data set that will trigger
* the worst case is nonexistent. Heapsort's only advantage over
* quicksort is that it requires little additional memory.
*
* @param vbase is base of array
* @param nmemb is item count
* @param size is item width
* @param compar is a callback returning <0, 0, or >0
* @see Knuth, Vol. 3, page 145.
* @see heapsort_r()
* @see mergesort()
* @see qsort()
*/
int
heapsort(void *vbase, size_t nmemb, size_t size,
int (*compar)(const void *, const void *))
{
return heapsort_r(vbase, nmemb, size, (void *)compar, 0);
}