/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: 2026-08-28 06:46

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	718k	{
49	718k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.6M	{
51	10.6M	if (COMPARE (src1, src2) <= 0)
52	9.42M	{
53	9.42M	dst++ = src1++;
54	9.42M	n1--;
55	9.42M	if (n1 == 0)
56	710k	break;
57	9.42M	}
58	1.25M	else
59	1.25M	{
60	1.25M	dst++ = src2++;
61	1.25M	n2--;
62	1.25M	if (n2 == 0)
63	7.21k	break;
64	1.25M	}
65	10.6M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	718k	if (n1 > 0)
68	7.21k	{
69	7.21k	if (dst != src1)
70	7.21k	do
71	21.4k	{
72	21.4k	dst++ = src1++;
73	21.4k	n1--;
74	21.4k	}
75	21.4k	while (n1 > 0);
76	7.21k	}
77	710k	else /* n2 > 0 */
78	710k	{
79	710k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	710k	}
87	718k	}
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	1.41M	{
100	1.41M	switch (n)
101	1.41M	{
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	653k	case 2:
109		/* Trivial case. */
110	653k	if (COMPARE (&src[0], &src[1]) <= 0)
111	648k	{
112		/* src[0] <= src[1] */
113	648k	dst[0] = src[0];
114	648k	dst[1] = src[1];
115	648k	}
116	4.32k	else
117	4.32k	{
118	4.32k	dst[0] = src[1];
119	4.32k	dst[1] = src[0];
120	4.32k	}
121	653k	break;
122	64.9k	case 3:
123		/* Simple case. */
124	64.9k	if (COMPARE (&src[0], &src[1]) <= 0)
125	60.0k	{
126	60.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	55.5k	{
128		/* src[0] <= src[1] <= src[2] */
129	55.5k	dst[0] = src[0];
130	55.5k	dst[1] = src[1];
131	55.5k	dst[2] = src[2];
132	55.5k	}
133	4.58k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	3.04k	{
135		/* src[0] <= src[2] < src[1] */
136	3.04k	dst[0] = src[0];
137	3.04k	dst[1] = src[2];
138	3.04k	dst[2] = src[1];
139	3.04k	}
140	1.53k	else
141	1.53k	{
142		/* src[2] < src[0] <= src[1] */
143	1.53k	dst[0] = src[2];
144	1.53k	dst[1] = src[0];
145	1.53k	dst[2] = src[1];
146	1.53k	}
147	60.0k	}
148	4.91k	else
149	4.91k	{
150	4.91k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.98k	{
152		/* src[1] < src[0] <= src[2] */
153	1.98k	dst[0] = src[1];
154	1.98k	dst[1] = src[0];
155	1.98k	dst[2] = src[2];
156	1.98k	}
157	2.92k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	2.08k	{
159		/* src[1] <= src[2] < src[0] */
160	2.08k	dst[0] = src[1];
161	2.08k	dst[1] = src[2];
162	2.08k	dst[2] = src[0];
163	2.08k	}
164	844	else
165	844	{
166		/* src[2] < src[1] < src[0] */
167	844	dst[0] = src[2];
168	844	dst[1] = src[1];
169	844	dst[2] = src[0];
170	844	}
171	4.91k	}
172	64.9k	break;
173	692k	default:
174	692k	{
175	692k	size_t n1 = n / 2;
176	692k	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	692k	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	692k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	692k	merge (tmp, n1, dst + n1, n2, dst);
184	692k	}
185	692k	break;
186	1.41M	}
187	1.41M	}
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	1.72M	{
194	1.72M	switch (n)
195	1.72M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.68M	case 2:
201		/* Trivial case. */
202	1.68M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.68M	{
204		/* src[0] <= src[1] */
205	1.68M	}
206	1.32k	else
207	1.32k	{
208	1.32k	ELEMENT t = src[0];
209	1.32k	src[0] = src[1];
210	1.32k	src[1] = t;
211	1.32k	}
212	1.68M	break;
213	18.2k	case 3:
214		/* Simple case. */
215	18.2k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.4k	{
217	14.4k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.7k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.7k	}
221	2.67k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.35k	{
223		/* src[0] <= src[2] < src[1] */
224	1.35k	ELEMENT t = src[1];
225	1.35k	src[1] = src[2];
226	1.35k	src[2] = t;
227	1.35k	}
228	1.31k	else
229	1.31k	{
230		/* src[2] < src[0] <= src[1] */
231	1.31k	ELEMENT t = src[0];
232	1.31k	src[0] = src[2];
233	1.31k	src[2] = src[1];
234	1.31k	src[1] = t;
235	1.31k	}
236	14.4k	}
237	3.77k	else
238	3.77k	{
239	3.77k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.22k	{
241		/* src[1] < src[0] <= src[2] */
242	1.22k	ELEMENT t = src[0];
243	1.22k	src[0] = src[1];
244	1.22k	src[1] = t;
245	1.22k	}
246	2.55k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.49k	{
248		/* src[1] <= src[2] < src[0] */
249	1.49k	ELEMENT t = src[0];
250	1.49k	src[0] = src[1];
251	1.49k	src[1] = src[2];
252	1.49k	src[2] = t;
253	1.49k	}
254	1.06k	else
255	1.06k	{
256		/* src[2] < src[1] < src[0] */
257	1.06k	ELEMENT t = src[0];
258	1.06k	src[0] = src[2];
259	1.06k	src[2] = t;
260	1.06k	}
261	3.77k	}
262	18.2k	break;
263	25.1k	default:
264	25.1k	{
265	25.1k	size_t n1 = n / 2;
266	25.1k	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	25.1k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	25.1k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	25.1k	merge (tmp, n1, src + n1, n2, src);
274	25.1k	}
275	25.1k	break;
276	1.72M	}
277	1.72M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC