/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: 2026-02-20 06:21

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	705k	{
49	705k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.2M	{
51	10.2M	if (COMPARE (src1, src2) <= 0)
52	9.13M	{
53	9.13M	dst++ = src1++;
54	9.13M	n1--;
55	9.13M	if (n1 == 0)
56	700k	break;
57	9.13M	}
58	1.09M	else
59	1.09M	{
60	1.09M	dst++ = src2++;
61	1.09M	n2--;
62	1.09M	if (n2 == 0)
63	5.85k	break;
64	1.09M	}
65	10.2M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	705k	if (n1 > 0)
68	5.85k	{
69	5.85k	if (dst != src1)
70	5.85k	do
71	16.5k	{
72	16.5k	dst++ = src1++;
73	16.5k	n1--;
74	16.5k	}
75	16.5k	while (n1 > 0);
76	5.85k	}
77	700k	else /* n2 > 0 */
78	700k	{
79	700k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	700k	}
87	705k	}
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	1.38M	{
100	1.38M	switch (n)
101	1.38M	{
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	643k	case 2:
109		/* Trivial case. */
110	643k	if (COMPARE (&src[0], &src[1]) <= 0)
111	641k	{
112		/* src[0] <= src[1] */
113	641k	dst[0] = src[0];
114	641k	dst[1] = src[1];
115	641k	}
116	2.61k	else
117	2.61k	{
118	2.61k	dst[0] = src[1];
119	2.61k	dst[1] = src[0];
120	2.61k	}
121	643k	break;
122	62.1k	case 3:
123		/* Simple case. */
124	62.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	55.9k	{
126	55.9k	if (COMPARE (&src[1], &src[2]) <= 0)
127	53.0k	{
128		/* src[0] <= src[1] <= src[2] */
129	53.0k	dst[0] = src[0];
130	53.0k	dst[1] = src[1];
131	53.0k	dst[2] = src[2];
132	53.0k	}
133	2.89k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.00k	{
135		/* src[0] <= src[2] < src[1] */
136	2.00k	dst[0] = src[0];
137	2.00k	dst[1] = src[2];
138	2.00k	dst[2] = src[1];
139	2.00k	}
140	895	else
141	895	{
142		/* src[2] < src[0] <= src[1] */
143	895	dst[0] = src[2];
144	895	dst[1] = src[0];
145	895	dst[2] = src[1];
146	895	}
147	55.9k	}
148	6.23k	else
149	6.23k	{
150	6.23k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.44k	{
152		/* src[1] < src[0] <= src[2] */
153	1.44k	dst[0] = src[1];
154	1.44k	dst[1] = src[0];
155	1.44k	dst[2] = src[2];
156	1.44k	}
157	4.79k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.29k	{
159		/* src[1] <= src[2] < src[0] */
160	1.29k	dst[0] = src[1];
161	1.29k	dst[1] = src[2];
162	1.29k	dst[2] = src[0];
163	1.29k	}
164	3.50k	else
165	3.50k	{
166		/* src[2] < src[1] < src[0] */
167	3.50k	dst[0] = src[2];
168	3.50k	dst[1] = src[1];
169	3.50k	dst[2] = src[0];
170	3.50k	}
171	6.23k	}
172	62.1k	break;
173	678k	default:
174	678k	{
175	678k	size_t n1 = n / 2;
176	678k	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	678k	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	678k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	678k	merge (tmp, n1, dst + n1, n2, dst);
184	678k	}
185	678k	break;
186	1.38M	}
187	1.38M	}
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	1.47M	{
194	1.47M	switch (n)
195	1.47M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.42M	case 2:
201		/* Trivial case. */
202	1.42M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.42M	{
204		/* src[0] <= src[1] */
205	1.42M	}
206	1.29k	else
207	1.29k	{
208	1.29k	ELEMENT t = src[0];
209	1.29k	src[0] = src[1];
210	1.29k	src[1] = t;
211	1.29k	}
212	1.42M	break;
213	18.9k	case 3:
214		/* Simple case. */
215	18.9k	if (COMPARE (&src[0], &src[1]) <= 0)
216	15.3k	{
217	15.3k	if (COMPARE (&src[1], &src[2]) <= 0)
218	12.8k	{
219		/* src[0] <= src[1] <= src[2] */
220	12.8k	}
221	2.44k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.17k	{
223		/* src[0] <= src[2] < src[1] */
224	1.17k	ELEMENT t = src[1];
225	1.17k	src[1] = src[2];
226	1.17k	src[2] = t;
227	1.17k	}
228	1.26k	else
229	1.26k	{
230		/* src[2] < src[0] <= src[1] */
231	1.26k	ELEMENT t = src[0];
232	1.26k	src[0] = src[2];
233	1.26k	src[2] = src[1];
234	1.26k	src[1] = t;
235	1.26k	}
236	15.3k	}
237	3.57k	else
238	3.57k	{
239	3.57k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.05k	{
241		/* src[1] < src[0] <= src[2] */
242	1.05k	ELEMENT t = src[0];
243	1.05k	src[0] = src[1];
244	1.05k	src[1] = t;
245	1.05k	}
246	2.52k	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	1.16k	else
255	1.16k	{
256		/* src[2] < src[1] < src[0] */
257	1.16k	ELEMENT t = src[0];
258	1.16k	src[0] = src[2];
259	1.16k	src[2] = t;
260	1.16k	}
261	3.57k	}
262	18.9k	break;
263	27.5k	default:
264	27.5k	{
265	27.5k	size_t n1 = n / 2;
266	27.5k	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	27.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	27.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	27.5k	merge (tmp, n1, src + n1, n2, src);
274	27.5k	}
275	27.5k	break;
276	1.47M	}
277	1.47M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC