/src/libunistring/lib/array-mergesort.h

Source
/* Stable-sorting of an array using mergesort.
   Copyright (C) 2009-2026 Free Software Foundation, Inc.
   Written by Bruno Haible <bruno@clisp.org>, 2009.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* This file implements stable sorting of an array, using the mergesort
   algorithm.
   Worst-case running time for an array of length N is O(N log N).
   Unlike the mpsort module, the algorithm here attempts to minimize not
   only the number of comparisons, but also the number of copying operations.

   Before including this file, you need to define
     ELEMENT      The type of every array element.
     COMPARE      A two-argument macro that takes two 'const ELEMENT *'
                  pointers and returns a negative, zero, or positive 'int'
                  value if the element pointed to by the first argument is,
                  respectively, less, equal, or greater than the element
                  pointed to by the second argument.
     STATIC       The storage class of the functions being defined.
     STATIC_FROMTO  (Optional.) Overrides STATIC for the 'merge_sort_fromto'
                    function.
   Before including this file, you also need to include:
     #include <stddef.h>
 */

/* Merge the sorted arrays src1[0..n1-1] and src2[0..n2-1] into
   dst[0..n1+n2-1].  In case of ambiguity, put the elements of src1
   before the elements of src2.
   n1 and n2 must be > 0.
   The arrays src1 and src2 must not overlap the dst array, except that
   src1 may be dst[n2..n1+n2-1], or src2 may be dst[n1..n1+n2-1].  */
static void
merge (const ELEMENT *src1, size_t n1,
       const ELEMENT *src2, size_t n2,
       ELEMENT *dst)
{
  for (;;) /* while (n1 > 0 && n2 > 0) */
    {
      if (COMPARE (src1, src2) <= 0)
        {
          *dst++ = *src1++;
          n1--;
          if (n1 == 0)
            break;
        }
      else
        {
          *dst++ = *src2++;
          n2--;
          if (n2 == 0)
            break;
        }
    }
  /* Here n1 == 0 || n2 == 0 but also n1 > 0 || n2 > 0.  */
  if (n1 > 0)
    {
      if (dst != src1)
        do
          {
            *dst++ = *src1++;
            n1--;
          }
        while (n1 > 0);
    }
  else /* n2 > 0 */
    {
      if (dst != src2)
        do
          {
            *dst++ = *src2++;
            n2--;
          }
        while (n2 > 0);
    }
}

/* Sort src[0..n-1] into dst[0..n-1], using tmp[0..n/2-1] as temporary
   (scratch) storage.
   The arrays src, dst, tmp must not overlap.  */
#ifdef STATIC_FROMTO
STATIC_FROMTO
#else
STATIC
#endif
void
merge_sort_fromto (const ELEMENT *src, ELEMENT *dst, size_t n, ELEMENT *tmp)
{
  switch (n)
    {
    case 0:
      return;
    case 1:
      /* Nothing to do.  */
      dst[0] = src[0];
      return;
    case 2:
      /* Trivial case.  */
      if (COMPARE (&src[0], &src[1]) <= 0)
        {
          /* src[0] <= src[1] */
          dst[0] = src[0];
          dst[1] = src[1];
        }
      else
        {
          dst[0] = src[1];
          dst[1] = src[0];
        }
      break;
    case 3:
      /* Simple case.  */
      if (COMPARE (&src[0], &src[1]) <= 0)
        {
          if (COMPARE (&src[1], &src[2]) <= 0)
            {
              /* src[0] <= src[1] <= src[2] */
              dst[0] = src[0];
              dst[1] = src[1];
              dst[2] = src[2];
            }
          else if (COMPARE (&src[0], &src[2]) <= 0)
            {
              /* src[0] <= src[2] < src[1] */
              dst[0] = src[0];
              dst[1] = src[2];
              dst[2] = src[1];
            }
          else
            {
              /* src[2] < src[0] <= src[1] */
              dst[0] = src[2];
              dst[1] = src[0];
              dst[2] = src[1];
            }
        }
      else
        {
          if (COMPARE (&src[0], &src[2]) <= 0)
            {
              /* src[1] < src[0] <= src[2] */
              dst[0] = src[1];
              dst[1] = src[0];
              dst[2] = src[2];
            }
          else if (COMPARE (&src[1], &src[2]) <= 0)
            {
              /* src[1] <= src[2] < src[0] */
              dst[0] = src[1];
              dst[1] = src[2];
              dst[2] = src[0];
            }
          else
            {
              /* src[2] < src[1] < src[0] */
              dst[0] = src[2];
              dst[1] = src[1];
              dst[2] = src[0];
            }
        }
      break;
    default:
      {
        size_t n1 = n / 2;
        size_t n2 = (n + 1) / 2;
        /* Note: n1 + n2 = n, n1 <= n2.  */
        /* Sort src[n1..n-1] into dst[n1..n-1], scratching tmp[0..n2/2-1].  */
        merge_sort_fromto (src + n1, dst + n1, n2, tmp);
        /* Sort src[0..n1-1] into tmp[0..n1-1], scratching dst[0..n1-1].  */
        merge_sort_fromto (src, tmp, n1, dst);
        /* Merge the two half results.  */
        merge (tmp, n1, dst + n1, n2, dst);
      }
      break;
    }
}

/* Sort src[0..n-1], using tmp[0..n-1] as temporary (scratch) storage.
   The arrays src, tmp must not overlap. */
STATIC void
merge_sort_inplace (ELEMENT *src, size_t n, ELEMENT *tmp)
{
  switch (n)
    {
    case 0:
    case 1:
      /* Nothing to do.  */
      return;
    case 2:
      /* Trivial case.  */
      if (COMPARE (&src[0], &src[1]) <= 0)
        {
          /* src[0] <= src[1] */
        }
      else
        {
          ELEMENT t = src[0];
          src[0] = src[1];
          src[1] = t;
        }
      break;
    case 3:
      /* Simple case.  */
      if (COMPARE (&src[0], &src[1]) <= 0)
        {
          if (COMPARE (&src[1], &src[2]) <= 0)
            {
              /* src[0] <= src[1] <= src[2] */
            }
          else if (COMPARE (&src[0], &src[2]) <= 0)
            {
              /* src[0] <= src[2] < src[1] */
              ELEMENT t = src[1];
              src[1] = src[2];
              src[2] = t;
            }
          else
            {
              /* src[2] < src[0] <= src[1] */
              ELEMENT t = src[0];
              src[0] = src[2];
              src[2] = src[1];
              src[1] = t;
            }
        }
      else
        {
          if (COMPARE (&src[0], &src[2]) <= 0)
            {
              /* src[1] < src[0] <= src[2] */
              ELEMENT t = src[0];
              src[0] = src[1];
              src[1] = t;
            }
          else if (COMPARE (&src[1], &src[2]) <= 0)
            {
              /* src[1] <= src[2] < src[0] */
              ELEMENT t = src[0];
              src[0] = src[1];
              src[1] = src[2];
              src[2] = t;
            }
          else
            {
              /* src[2] < src[1] < src[0] */
              ELEMENT t = src[0];
              src[0] = src[2];
              src[2] = t;
            }
        }
      break;
    default:
      {
        size_t n1 = n / 2;
        size_t n2 = (n + 1) / 2;
        /* Note: n1 + n2 = n, n1 <= n2.  */
        /* Sort src[n1..n-1], scratching tmp[0..n2-1].  */
        merge_sort_inplace (src + n1, n2, tmp);
        /* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2*n1-1].  */
        merge_sort_fromto (src, tmp, n1, tmp + n1);
        /* Merge the two half results.  */
        merge (tmp, n1, src + n1, n2, src);
      }
      break;
    }
}

#undef ELEMENT
#undef COMPARE
#undef STATIC

Coverage Report

Created: 2026-08-20 06:19

Line	Count	Source
1		/* Stable-sorting of an array using mergesort.
2		Copyright (C) 2009-2026 Free Software Foundation, Inc.
3		Written by Bruno Haible <bruno@clisp.org>, 2009.
4
5		This file is free software: you can redistribute it and/or modify
6		it under the terms of the GNU Lesser General Public License as
7		published by the Free Software Foundation; either version 2.1 of the
8		License, or (at your option) any later version.
9
10		This file is distributed in the hope that it will be useful,
11		but WITHOUT ANY WARRANTY; without even the implied warranty of
12		MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13		GNU Lesser General Public License for more details.
14
15		You should have received a copy of the GNU Lesser General Public License
16		along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18		/* This file implements stable sorting of an array, using the mergesort
19		algorithm.
20		Worst-case running time for an array of length N is O(N log N).
21		Unlike the mpsort module, the algorithm here attempts to minimize not
22		only the number of comparisons, but also the number of copying operations.
23
24		Before including this file, you need to define
25		ELEMENT The type of every array element.
26		COMPARE A two-argument macro that takes two 'const ELEMENT *'
27		pointers and returns a negative, zero, or positive 'int'
28		value if the element pointed to by the first argument is,
29		respectively, less, equal, or greater than the element
30		pointed to by the second argument.
31		STATIC The storage class of the functions being defined.
32		STATIC_FROMTO (Optional.) Overrides STATIC for the 'merge_sort_fromto'
33		function.
34		Before including this file, you also need to include:
35		#include <stddef.h>
36		*/
37
38		/* Merge the sorted arrays src1[0..n1-1] and src2[0..n2-1] into
39		dst[0..n1+n2-1]. In case of ambiguity, put the elements of src1
40		before the elements of src2.
41		n1 and n2 must be > 0.
42		The arrays src1 and src2 must not overlap the dst array, except that
43		src1 may be dst[n2..n1+n2-1], or src2 may be dst[n1..n1+n2-1]. */
44		static void
45		merge (const ELEMENT *src1, size_t n1,
46		const ELEMENT *src2, size_t n2,
47		ELEMENT *dst)
48	759k	{
49	759k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	11.1M	{
51	11.1M	if (COMPARE (src1, src2) <= 0)
52	9.82M	{
53	9.82M	dst++ = src1++;
54	9.82M	n1--;
55	9.82M	if (n1 == 0)
56	752k	break;
57	9.82M	}
58	1.31M	else
59	1.31M	{
60	1.31M	dst++ = src2++;
61	1.31M	n2--;
62	1.31M	if (n2 == 0)
63	7.18k	break;
64	1.31M	}
65	11.1M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	759k	if (n1 > 0)
68	7.18k	{
69	7.18k	if (dst != src1)
70	7.18k	do
71	24.5k	{
72	24.5k	dst++ = src1++;
73	24.5k	n1--;
74	24.5k	}
75	24.5k	while (n1 > 0);
76	7.18k	}
77	752k	else /* n2 > 0 */
78	752k	{
79	752k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	752k	}
87	759k	}
88
89		/* Sort src[0..n-1] into dst[0..n-1], using tmp[0..n/2-1] as temporary
90		(scratch) storage.
91		The arrays src, dst, tmp must not overlap. */
92		#ifdef STATIC_FROMTO
93		STATIC_FROMTO
94		#else
95		STATIC
96		#endif
97		void
98		merge_sort_fromto (const ELEMENT src, ELEMENT dst, size_t n, ELEMENT *tmp)
99	1.48M	{
100	1.48M	switch (n)
101	1.48M	{
102	0	case 0:
103	0	return;
104	0	case 1:
105		/* Nothing to do. */
106	0	dst[0] = src[0];
107	0	return;
108	678k	case 2:
109		/* Trivial case. */
110	678k	if (COMPARE (&src[0], &src[1]) <= 0)
111	674k	{
112		/* src[0] <= src[1] */
113	674k	dst[0] = src[0];
114	674k	dst[1] = src[1];
115	674k	}
116	4.55k	else
117	4.55k	{
118	4.55k	dst[0] = src[1];
119	4.55k	dst[1] = src[0];
120	4.55k	}
121	678k	break;
122	80.4k	case 3:
123		/* Simple case. */
124	80.4k	if (COMPARE (&src[0], &src[1]) <= 0)
125	75.4k	{
126	75.4k	if (COMPARE (&src[1], &src[2]) <= 0)
127	71.0k	{
128		/* src[0] <= src[1] <= src[2] */
129	71.0k	dst[0] = src[0];
130	71.0k	dst[1] = src[1];
131	71.0k	dst[2] = src[2];
132	71.0k	}
133	4.41k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.95k	{
135		/* src[0] <= src[2] < src[1] */
136	2.95k	dst[0] = src[0];
137	2.95k	dst[1] = src[2];
138	2.95k	dst[2] = src[1];
139	2.95k	}
140	1.46k	else
141	1.46k	{
142		/* src[2] < src[0] <= src[1] */
143	1.46k	dst[0] = src[2];
144	1.46k	dst[1] = src[0];
145	1.46k	dst[2] = src[1];
146	1.46k	}
147	75.4k	}
148	5.00k	else
149	5.00k	{
150	5.00k	if (COMPARE (&src[0], &src[2]) <= 0)
151	2.07k	{
152		/* src[1] < src[0] <= src[2] */
153	2.07k	dst[0] = src[1];
154	2.07k	dst[1] = src[0];
155	2.07k	dst[2] = src[2];
156	2.07k	}
157	2.93k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	2.12k	{
159		/* src[1] <= src[2] < src[0] */
160	2.12k	dst[0] = src[1];
161	2.12k	dst[1] = src[2];
162	2.12k	dst[2] = src[0];
163	2.12k	}
164	805	else
165	805	{
166		/* src[2] < src[1] < src[0] */
167	805	dst[0] = src[2];
168	805	dst[1] = src[1];
169	805	dst[2] = src[0];
170	805	}
171	5.00k	}
172	80.4k	break;
173	729k	default:
174	729k	{
175	729k	size_t n1 = n / 2;
176	729k	size_t n2 = (n + 1) / 2;
177		/* Note: n1 + n2 = n, n1 <= n2. */
178		/* Sort src[n1..n-1] into dst[n1..n-1], scratching tmp[0..n2/2-1]. */
179	729k	merge_sort_fromto (src + n1, dst + n1, n2, tmp);
180		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching dst[0..n1-1]. */
181	729k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	729k	merge (tmp, n1, dst + n1, n2, dst);
184	729k	}
185	729k	break;
186	1.48M	}
187	1.48M	}
188
189		/* Sort src[0..n-1], using tmp[0..n-1] as temporary (scratch) storage.
190		The arrays src, tmp must not overlap. */
191		STATIC void
192		merge_sort_inplace (ELEMENT src, size_t n, ELEMENT tmp)
193	1.67M	{
194	1.67M	switch (n)
195	1.67M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.62M	case 2:
201		/* Trivial case. */
202	1.62M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.62M	{
204		/* src[0] <= src[1] */
205	1.62M	}
206	1.85k	else
207	1.85k	{
208	1.85k	ELEMENT t = src[0];
209	1.85k	src[0] = src[1];
210	1.85k	src[1] = t;
211	1.85k	}
212	1.62M	break;
213	17.6k	case 3:
214		/* Simple case. */
215	17.6k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.8k	{
217	13.8k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.3k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.3k	}
221	2.43k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.26k	{
223		/* src[0] <= src[2] < src[1] */
224	1.26k	ELEMENT t = src[1];
225	1.26k	src[1] = src[2];
226	1.26k	src[2] = t;
227	1.26k	}
228	1.17k	else
229	1.17k	{
230		/* src[2] < src[0] <= src[1] */
231	1.17k	ELEMENT t = src[0];
232	1.17k	src[0] = src[2];
233	1.17k	src[2] = src[1];
234	1.17k	src[1] = t;
235	1.17k	}
236	13.8k	}
237	3.80k	else
238	3.80k	{
239	3.80k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.21k	{
241		/* src[1] < src[0] <= src[2] */
242	1.21k	ELEMENT t = src[0];
243	1.21k	src[0] = src[1];
244	1.21k	src[1] = t;
245	1.21k	}
246	2.59k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.54k	{
248		/* src[1] <= src[2] < src[0] */
249	1.54k	ELEMENT t = src[0];
250	1.54k	src[0] = src[1];
251	1.54k	src[1] = src[2];
252	1.54k	src[2] = t;
253	1.54k	}
254	1.04k	else
255	1.04k	{
256		/* src[2] < src[1] < src[0] */
257	1.04k	ELEMENT t = src[0];
258	1.04k	src[0] = src[2];
259	1.04k	src[2] = t;
260	1.04k	}
261	3.80k	}
262	17.6k	break;
263	29.3k	default:
264	29.3k	{
265	29.3k	size_t n1 = n / 2;
266	29.3k	size_t n2 = (n + 1) / 2;
267		/* Note: n1 + n2 = n, n1 <= n2. */
268		/* Sort src[n1..n-1], scratching tmp[0..n2-1]. */
269	29.3k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	29.3k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	29.3k	merge (tmp, n1, src + n1, n2, src);
274	29.3k	}
275	29.3k	break;
276	1.67M	}
277	1.67M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC