7a3775eeb4
llist_mergesort() has a loop for adding a new element to the ranks array and another one for rolling up said array into a single sorted list at the end. We can merge them, so that adding the last element rolls up the whole array. Handle the empty list before the main loop now because list can't be NULL anymore inside the loop. The result is shorter code and significantly less object text: main: __TEXT __DATA __OBJC others dec hex 652 0 0 4651 5303 14b7 mergesort.o With this patch: __TEXT __DATA __OBJC others dec hex 412 0 0 3441 3853 f0d mergesort.o Why is the change so big? The reduction is amplified by llist_merge() being inlined both before and after. Performance stays basically the same: main: 0071.12: llist_mergesort() unsorted 0.24(0.22+0.01) 0071.14: llist_mergesort() sorted 0.12(0.10+0.01) 0071.16: llist_mergesort() reversed 0.12(0.10+0.01) Benchmark 1: t/helper/test-tool mergesort test Time (mean ± σ): 109.0 ms ± 0.3 ms [User: 107.4 ms, System: 1.1 ms] Range (min … max): 108.7 ms … 109.6 ms 27 runs With this patch: 0071.12: llist_mergesort() unsorted 0.24(0.22+0.01) 0071.14: llist_mergesort() sorted 0.12(0.10+0.01) 0071.16: llist_mergesort() reversed 0.12(0.10+0.01) Benchmark 1: t/helper/test-tool mergesort test Time (mean ± σ): 109.2 ms ± 0.2 ms [User: 107.5 ms, System: 1.1 ms] Range (min … max): 108.9 ms … 109.6 ms 27 runs Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
84 lines
1.9 KiB
C
84 lines
1.9 KiB
C
#include "cache.h"
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#include "mergesort.h"
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/* Combine two sorted lists. Take from `list` on equality. */
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static void *llist_merge(void *list, void *other,
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void *(*get_next_fn)(const void *),
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void (*set_next_fn)(void *, void *),
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int (*compare_fn)(const void *, const void *))
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{
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void *result = list, *tail;
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if (compare_fn(list, other) > 0) {
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result = other;
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goto other;
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}
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for (;;) {
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do {
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tail = list;
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list = get_next_fn(list);
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if (!list) {
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set_next_fn(tail, other);
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return result;
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}
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} while (compare_fn(list, other) <= 0);
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set_next_fn(tail, other);
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other:
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do {
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tail = other;
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other = get_next_fn(other);
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if (!other) {
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set_next_fn(tail, list);
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return result;
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}
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} while (compare_fn(list, other) > 0);
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set_next_fn(tail, list);
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}
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}
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/*
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* Perform an iterative mergesort using an array of sublists.
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*
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* n is the number of items.
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* ranks[i] is undefined if n & 2^i == 0, and assumed empty.
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* ranks[i] contains a sublist of length 2^i otherwise.
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*
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* The number of bits in a void pointer limits the number of objects
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* that can be created, and thus the number of array elements necessary
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* to be able to sort any valid list.
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*
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* Adding an item to this array is like incrementing a binary number;
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* positional values for set bits correspond to sublist lengths.
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*/
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void *llist_mergesort(void *list,
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void *(*get_next_fn)(const void *),
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void (*set_next_fn)(void *, void *),
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int (*compare_fn)(const void *, const void *))
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{
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void *ranks[bitsizeof(void *)];
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size_t n = 0;
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if (!list)
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return NULL;
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for (;;) {
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int i;
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size_t m;
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void *next = get_next_fn(list);
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if (next)
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set_next_fn(list, NULL);
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for (i = 0, m = n;; i++, m >>= 1) {
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if (m & 1)
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list = llist_merge(ranks[i], list, get_next_fn,
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set_next_fn, compare_fn);
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else if (next)
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break;
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else if (!m)
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return list;
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}
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n++;
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ranks[i] = list;
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list = next;
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}
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}
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