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32 * @(#)merge.c 8.2 (Berkeley) 2/14/94
33 * $FreeBSD: src/lib/libc/stdlib/merge.c,v 1.8 2007/01/09 00:28:10 imp Exp $
37 * Hybrid exponential search/linear search merge sort with hybrid
38 * natural/pairwise first pass. Requires about .3% more comparisons
39 * for random data than LSMS with pairwise first pass alone.
40 * It works for objects as small as two bytes.
44 #define THRESHOLD 16 /* Best choice for natural merge cut-off. */
46 /* #define NATURAL to get hybrid natural merge.
47 * (The default is pairwise merging.)
50 #include <sys/param.h>
56 static void setup(u_char *, u_char *, size_t, size_t,
57 int (*)(const void *, const void *));
58 static void insertionsort(u_char *, size_t, size_t,
59 int (*)(const void *, const void *));
61 #define ISIZE sizeof(int)
62 #define PSIZE sizeof(u_char *)
63 #define ICOPY_LIST(src, dst, last) \
65 *(int*)dst = *(int*)src, src += ISIZE, dst += ISIZE; \
67 #define ICOPY_ELT(src, dst, i) \
69 *(int*) dst = *(int*) src, src += ISIZE, dst += ISIZE; \
72 #define CCOPY_LIST(src, dst, last) \
76 #define CCOPY_ELT(src, dst, i) \
82 * Find the next possible pointer head. (Trickery for forcing an array
83 * to do double duty as a linked list when objects do not align with word
86 /* Assumption: PSIZE is a power of 2. */
87 #define EVAL(p) (u_char **) \
89 (rounddown2((u_char *)p + PSIZE - 1 - (u_char *)0, PSIZE)))
92 * Arguments are as for qsort.
95 mergesort(void *base, size_t nmemb, size_t size,
96 int (*cmp)(const void *, const void *))
101 u_char *f1, *f2, *t, *b, *tp2, *q, *l1, *l2;
102 u_char *list2, *list1, *p2, *p, *last, **p1;
104 if (size < PSIZE / 2) { /* Pointers must fit into 2 * size. */
114 * Stupid subtraction for the Cray.
117 if (!(size % ISIZE) && !(((char *)base - (char *)0) % ISIZE))
120 if ((list2 = malloc(nmemb * size + PSIZE)) == NULL)
124 setup(list1, list2, nmemb, size, cmp);
125 last = list2 + nmemb * size;
127 while (*EVAL(list2) != last) {
130 for (tp2 = p2 = list2; p2 != last; p1 = EVAL(l2)) {
133 f2 = l1 = list1 + (p2 - list2);
136 l2 = list1 + (p2 - list2);
137 while (f1 < l1 && f2 < l2) {
138 if ((*cmp)(f1, f2) <= 0) {
147 if (!big) { /* here i = 0 */
148 while ((b += size) < t && cmp(q, b) >sense)
154 EXPONENTIAL: for (i = size; ; i <<= 1)
155 if ((p = (b + i)) >= t) {
156 if ((p = t - size) > b &&
157 (*cmp)(q, p) <= sense)
162 } else if ((*cmp)(q, p) <= sense) {
170 i = (((t - b) / size) >> 1) * size;
171 if ((*cmp)(q, p = b + i) <= sense)
177 FASTCASE: while (i > size)
179 p = b + (i >>= 1)) <= sense)
188 ICOPY_LIST(f2, tp2, b);
189 ICOPY_ELT(f1, tp2, i);
191 CCOPY_LIST(f2, tp2, b);
192 CCOPY_ELT(f1, tp2, i);
196 ICOPY_LIST(f1, tp2, b);
197 ICOPY_ELT(f2, tp2, i);
199 CCOPY_LIST(f1, tp2, b);
200 CCOPY_ELT(f2, tp2, i);
206 ICOPY_LIST(f2, tp2, l2);
208 CCOPY_LIST(f2, tp2, l2);
209 } else if (f1 < l1) {
211 ICOPY_LIST(f1, tp2, l1);
213 CCOPY_LIST(f1, tp2, l1);
217 tp2 = list1; /* swap list1, list2 */
220 last = list2 + nmemb*size;
223 memmove(list2, list1, nmemb*size);
230 #define swap(a, b) { \
234 tmp = *a; *a++ = *s; *s++ = tmp; \
238 #define reverse(bot, top) { \
243 tmp = *bot; *bot++ = *s; *s++ = tmp; \
250 * Optional hybrid natural/pairwise first pass. Eats up list1 in runs of
251 * increasing order, list2 in a corresponding linked list. Checks for runs
252 * when THRESHOLD/2 pairs compare with same sense. (Only used when NATURAL
253 * is defined. Otherwise simple pairwise merging is used.)
256 setup(u_char *list1, u_char *list2, size_t n, size_t size,
257 int (*cmp)(const void *, const void *))
259 int i, length, size2, tmp, sense;
260 u_char *f1, *f2, *s, *l2, *last, *p2;
264 insertionsort(list1, n, size, cmp);
265 *EVAL(list2) = (u_char*) list2 + n*size;
269 * Avoid running pointers out of bounds; limit n to evens
273 insertionsort(list1 + (n - i) * size, i, size, cmp);
274 last = list1 + size * (n - i);
275 *EVAL(list2 + (last - list1)) = list2 + n * size;
280 sense = (cmp(f1, f1 + size) > 0);
281 for (; f1 < last; sense = !sense) {
283 /* Find pairs with same sense. */
284 for (f2 = f1 + size2; f2 < last; f2 += size2) {
285 if ((cmp(f2, f2+ size) > 0) != sense)
289 if (length < THRESHOLD) { /* Pairwise merge */
291 p2 = *EVAL(p2) = f1 + size2 - list1 + list2;
293 swap (f1, f1 + size);
294 } while ((f1 += size2) < f2);
295 } else { /* Natural merge */
297 for (f2 = f1 + size2; f2 < l2; f2 += size2) {
298 if ((cmp(f2-size, f2) > 0) != sense) {
299 p2 = *EVAL(p2) = f2 - list1 + list2;
301 reverse(f1, f2-size);
306 reverse (f1, f2-size);
308 if (f2 < last || cmp(f2 - size, f2) > 0)
309 p2 = *EVAL(p2) = f2 - list1 + list2;
311 p2 = *EVAL(p2) = list2 + n*size;
314 #else /* pairwise merge only. */
315 for (f1 = list1, p2 = list2; f1 < last; f1 += size2) {
316 p2 = *EVAL(p2) = p2 + size2;
317 if (cmp (f1, f1 + size) > 0)
324 * This is to avoid out-of-bounds addresses in sorting the
328 insertionsort(u_char *a, size_t n, size_t size,
329 int (*cmp)(const void *, const void *))
331 u_char *ai, *s, *t, *u, tmp;
334 for (ai = a+size; --n >= 1; ai += size)
335 for (t = ai; t > a; t -= size) {