/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: 2026-07-05 07:04

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	663k	{
49	663k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.2M	{
51	10.2M	if (COMPARE (src1, src2) <= 0)
52	9.11M	{
53	9.11M	dst++ = src1++;
54	9.11M	n1--;
55	9.11M	if (n1 == 0)
56	657k	break;
57	9.11M	}
58	1.14M	else
59	1.14M	{
60	1.14M	dst++ = src2++;
61	1.14M	n2--;
62	1.14M	if (n2 == 0)
63	5.87k	break;
64	1.14M	}
65	10.2M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	663k	if (n1 > 0)
68	5.87k	{
69	5.87k	if (dst != src1)
70	5.87k	do
71	15.7k	{
72	15.7k	dst++ = src1++;
73	15.7k	n1--;
74	15.7k	}
75	15.7k	while (n1 > 0);
76	5.87k	}
77	657k	else /* n2 > 0 */
78	657k	{
79	657k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	657k	}
87	663k	}
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	1.31M	{
100	1.31M	switch (n)
101	1.31M	{
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	598k	case 2:
109		/* Trivial case. */
110	598k	if (COMPARE (&src[0], &src[1]) <= 0)
111	595k	{
112		/* src[0] <= src[1] */
113	595k	dst[0] = src[0];
114	595k	dst[1] = src[1];
115	595k	}
116	3.04k	else
117	3.04k	{
118	3.04k	dst[0] = src[1];
119	3.04k	dst[1] = src[0];
120	3.04k	}
121	598k	break;
122	64.5k	case 3:
123		/* Simple case. */
124	64.5k	if (COMPARE (&src[0], &src[1]) <= 0)
125	61.0k	{
126	61.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	57.6k	{
128		/* src[0] <= src[1] <= src[2] */
129	57.6k	dst[0] = src[0];
130	57.6k	dst[1] = src[1];
131	57.6k	dst[2] = src[2];
132	57.6k	}
133	3.39k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.19k	{
135		/* src[0] <= src[2] < src[1] */
136	2.19k	dst[0] = src[0];
137	2.19k	dst[1] = src[2];
138	2.19k	dst[2] = src[1];
139	2.19k	}
140	1.20k	else
141	1.20k	{
142		/* src[2] < src[0] <= src[1] */
143	1.20k	dst[0] = src[2];
144	1.20k	dst[1] = src[0];
145	1.20k	dst[2] = src[1];
146	1.20k	}
147	61.0k	}
148	3.52k	else
149	3.52k	{
150	3.52k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.55k	{
152		/* src[1] < src[0] <= src[2] */
153	1.55k	dst[0] = src[1];
154	1.55k	dst[1] = src[0];
155	1.55k	dst[2] = src[2];
156	1.55k	}
157	1.97k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.34k	{
159		/* src[1] <= src[2] < src[0] */
160	1.34k	dst[0] = src[1];
161	1.34k	dst[1] = src[2];
162	1.34k	dst[2] = src[0];
163	1.34k	}
164	632	else
165	632	{
166		/* src[2] < src[1] < src[0] */
167	632	dst[0] = src[2];
168	632	dst[1] = src[1];
169	632	dst[2] = src[0];
170	632	}
171	3.52k	}
172	64.5k	break;
173	649k	default:
174	649k	{
175	649k	size_t n1 = n / 2;
176	649k	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	649k	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	649k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	649k	merge (tmp, n1, dst + n1, n2, dst);
184	649k	}
185	649k	break;
186	1.31M	}
187	1.31M	}
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	1.69M	{
194	1.69M	switch (n)
195	1.69M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.67M	case 2:
201		/* Trivial case. */
202	1.67M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.67M	{
204		/* src[0] <= src[1] */
205	1.67M	}
206	1.81k	else
207	1.81k	{
208	1.81k	ELEMENT t = src[0];
209	1.81k	src[0] = src[1];
210	1.81k	src[1] = t;
211	1.81k	}
212	1.67M	break;
213	7.03k	case 3:
214		/* Simple case. */
215	7.03k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.95k	{
217	4.95k	if (COMPARE (&src[1], &src[2]) <= 0)
218	2.57k	{
219		/* src[0] <= src[1] <= src[2] */
220	2.57k	}
221	2.37k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.41k	{
223		/* src[0] <= src[2] < src[1] */
224	1.41k	ELEMENT t = src[1];
225	1.41k	src[1] = src[2];
226	1.41k	src[2] = t;
227	1.41k	}
228	953	else
229	953	{
230		/* src[2] < src[0] <= src[1] */
231	953	ELEMENT t = src[0];
232	953	src[0] = src[2];
233	953	src[2] = src[1];
234	953	src[1] = t;
235	953	}
236	4.95k	}
237	2.08k	else
238	2.08k	{
239	2.08k	if (COMPARE (&src[0], &src[2]) <= 0)
240	643	{
241		/* src[1] < src[0] <= src[2] */
242	643	ELEMENT t = src[0];
243	643	src[0] = src[1];
244	643	src[1] = t;
245	643	}
246	1.44k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	747	{
248		/* src[1] <= src[2] < src[0] */
249	747	ELEMENT t = src[0];
250	747	src[0] = src[1];
251	747	src[1] = src[2];
252	747	src[2] = t;
253	747	}
254	696	else
255	696	{
256		/* src[2] < src[1] < src[0] */
257	696	ELEMENT t = src[0];
258	696	src[0] = src[2];
259	696	src[2] = t;
260	696	}
261	2.08k	}
262	7.03k	break;
263	13.5k	default:
264	13.5k	{
265	13.5k	size_t n1 = n / 2;
266	13.5k	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	13.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	13.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	13.5k	merge (tmp, n1, src + n1, n2, src);
274	13.5k	}
275	13.5k	break;
276	1.69M	}
277	1.69M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC