/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: 2026-03-07 06:49

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	713k	{
49	713k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.7M	{
51	10.7M	if (COMPARE (src1, src2) <= 0)
52	9.55M	{
53	9.55M	dst++ = src1++;
54	9.55M	n1--;
55	9.55M	if (n1 == 0)
56	708k	break;
57	9.55M	}
58	1.15M	else
59	1.15M	{
60	1.15M	dst++ = src2++;
61	1.15M	n2--;
62	1.15M	if (n2 == 0)
63	5.35k	break;
64	1.15M	}
65	10.7M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	713k	if (n1 > 0)
68	5.35k	{
69	5.35k	if (dst != src1)
70	5.35k	do
71	16.7k	{
72	16.7k	dst++ = src1++;
73	16.7k	n1--;
74	16.7k	}
75	16.7k	while (n1 > 0);
76	5.35k	}
77	708k	else /* n2 > 0 */
78	708k	{
79	708k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	708k	}
87	713k	}
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	1.40M	{
100	1.40M	switch (n)
101	1.40M	{
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	641k	case 2:
109		/* Trivial case. */
110	641k	if (COMPARE (&src[0], &src[1]) <= 0)
111	638k	{
112		/* src[0] <= src[1] */
113	638k	dst[0] = src[0];
114	638k	dst[1] = src[1];
115	638k	}
116	2.39k	else
117	2.39k	{
118	2.39k	dst[0] = src[1];
119	2.39k	dst[1] = src[0];
120	2.39k	}
121	641k	break;
122	72.5k	case 3:
123		/* Simple case. */
124	72.5k	if (COMPARE (&src[0], &src[1]) <= 0)
125	69.1k	{
126	69.1k	if (COMPARE (&src[1], &src[2]) <= 0)
127	66.2k	{
128		/* src[0] <= src[1] <= src[2] */
129	66.2k	dst[0] = src[0];
130	66.2k	dst[1] = src[1];
131	66.2k	dst[2] = src[2];
132	66.2k	}
133	2.81k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.93k	{
135		/* src[0] <= src[2] < src[1] */
136	1.93k	dst[0] = src[0];
137	1.93k	dst[1] = src[2];
138	1.93k	dst[2] = src[1];
139	1.93k	}
140	875	else
141	875	{
142		/* src[2] < src[0] <= src[1] */
143	875	dst[0] = src[2];
144	875	dst[1] = src[0];
145	875	dst[2] = src[1];
146	875	}
147	69.1k	}
148	3.39k	else
149	3.39k	{
150	3.39k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.49k	{
152		/* src[1] < src[0] <= src[2] */
153	1.49k	dst[0] = src[1];
154	1.49k	dst[1] = src[0];
155	1.49k	dst[2] = src[2];
156	1.49k	}
157	1.89k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.10k	{
159		/* src[1] <= src[2] < src[0] */
160	1.10k	dst[0] = src[1];
161	1.10k	dst[1] = src[2];
162	1.10k	dst[2] = src[0];
163	1.10k	}
164	794	else
165	794	{
166		/* src[2] < src[1] < src[0] */
167	794	dst[0] = src[2];
168	794	dst[1] = src[1];
169	794	dst[2] = src[0];
170	794	}
171	3.39k	}
172	72.5k	break;
173	691k	default:
174	691k	{
175	691k	size_t n1 = n / 2;
176	691k	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	691k	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	691k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	691k	merge (tmp, n1, dst + n1, n2, dst);
184	691k	}
185	691k	break;
186	1.40M	}
187	1.40M	}
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	1.42M	{
194	1.42M	switch (n)
195	1.42M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.38M	case 2:
201		/* Trivial case. */
202	1.38M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.38M	{
204		/* src[0] <= src[1] */
205	1.38M	}
206	1.01k	else
207	1.01k	{
208	1.01k	ELEMENT t = src[0];
209	1.01k	src[0] = src[1];
210	1.01k	src[1] = t;
211	1.01k	}
212	1.38M	break;
213	16.9k	case 3:
214		/* Simple case. */
215	16.9k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.2k	{
217	13.2k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.0k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.0k	}
221	2.28k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.24k	{
223		/* src[0] <= src[2] < src[1] */
224	1.24k	ELEMENT t = src[1];
225	1.24k	src[1] = src[2];
226	1.24k	src[2] = t;
227	1.24k	}
228	1.03k	else
229	1.03k	{
230		/* src[2] < src[0] <= src[1] */
231	1.03k	ELEMENT t = src[0];
232	1.03k	src[0] = src[2];
233	1.03k	src[2] = src[1];
234	1.03k	src[1] = t;
235	1.03k	}
236	13.2k	}
237	3.64k	else
238	3.64k	{
239	3.64k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.17k	{
241		/* src[1] < src[0] <= src[2] */
242	1.17k	ELEMENT t = src[0];
243	1.17k	src[0] = src[1];
244	1.17k	src[1] = t;
245	1.17k	}
246	2.47k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.35k	{
248		/* src[1] <= src[2] < src[0] */
249	1.35k	ELEMENT t = src[0];
250	1.35k	src[0] = src[1];
251	1.35k	src[1] = src[2];
252	1.35k	src[2] = t;
253	1.35k	}
254	1.11k	else
255	1.11k	{
256		/* src[2] < src[1] < src[0] */
257	1.11k	ELEMENT t = src[0];
258	1.11k	src[0] = src[2];
259	1.11k	src[2] = t;
260	1.11k	}
261	3.64k	}
262	16.9k	break;
263	22.5k	default:
264	22.5k	{
265	22.5k	size_t n1 = n / 2;
266	22.5k	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	22.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	22.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	22.5k	merge (tmp, n1, src + n1, n2, src);
274	22.5k	}
275	22.5k	break;
276	1.42M	}
277	1.42M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC