/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: 2026-02-05 06:23

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	668k	{
49	668k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.93M	{
51	9.93M	if (COMPARE (src1, src2) <= 0)
52	8.84M	{
53	8.84M	dst++ = src1++;
54	8.84M	n1--;
55	8.84M	if (n1 == 0)
56	663k	break;
57	8.84M	}
58	1.08M	else
59	1.08M	{
60	1.08M	dst++ = src2++;
61	1.08M	n2--;
62	1.08M	if (n2 == 0)
63	4.76k	break;
64	1.08M	}
65	9.93M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	668k	if (n1 > 0)
68	4.76k	{
69	4.76k	if (dst != src1)
70	4.76k	do
71	13.9k	{
72	13.9k	dst++ = src1++;
73	13.9k	n1--;
74	13.9k	}
75	13.9k	while (n1 > 0);
76	4.76k	}
77	663k	else /* n2 > 0 */
78	663k	{
79	663k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	663k	}
87	668k	}
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	612k	case 2:
109		/* Trivial case. */
110	612k	if (COMPARE (&src[0], &src[1]) <= 0)
111	610k	{
112		/* src[0] <= src[1] */
113	610k	dst[0] = src[0];
114	610k	dst[1] = src[1];
115	610k	}
116	1.84k	else
117	1.84k	{
118	1.84k	dst[0] = src[1];
119	1.84k	dst[1] = src[0];
120	1.84k	}
121	612k	break;
122	55.8k	case 3:
123		/* Simple case. */
124	55.8k	if (COMPARE (&src[0], &src[1]) <= 0)
125	53.0k	{
126	53.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	50.8k	{
128		/* src[0] <= src[1] <= src[2] */
129	50.8k	dst[0] = src[0];
130	50.8k	dst[1] = src[1];
131	50.8k	dst[2] = src[2];
132	50.8k	}
133	2.19k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.38k	{
135		/* src[0] <= src[2] < src[1] */
136	1.38k	dst[0] = src[0];
137	1.38k	dst[1] = src[2];
138	1.38k	dst[2] = src[1];
139	1.38k	}
140	808	else
141	808	{
142		/* src[2] < src[0] <= src[1] */
143	808	dst[0] = src[2];
144	808	dst[1] = src[0];
145	808	dst[2] = src[1];
146	808	}
147	53.0k	}
148	2.84k	else
149	2.84k	{
150	2.84k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.00k	{
152		/* src[1] < src[0] <= src[2] */
153	1.00k	dst[0] = src[1];
154	1.00k	dst[1] = src[0];
155	1.00k	dst[2] = src[2];
156	1.00k	}
157	1.84k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	846	{
159		/* src[1] <= src[2] < src[0] */
160	846	dst[0] = src[1];
161	846	dst[1] = src[2];
162	846	dst[2] = src[0];
163	846	}
164	999	else
165	999	{
166		/* src[2] < src[1] < src[0] */
167	999	dst[0] = src[2];
168	999	dst[1] = src[1];
169	999	dst[2] = src[0];
170	999	}
171	2.84k	}
172	55.8k	break;
173	647k	default:
174	647k	{
175	647k	size_t n1 = n / 2;
176	647k	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	647k	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	647k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	647k	merge (tmp, n1, dst + n1, n2, dst);
184	647k	}
185	647k	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	1.46M	{
194	1.46M	switch (n)
195	1.46M	{
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	863	else
207	863	{
208	863	ELEMENT t = src[0];
209	863	src[0] = src[1];
210	863	src[1] = t;
211	863	}
212	1.42M	break;
213	17.5k	case 3:
214		/* Simple case. */
215	17.5k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.9k	{
217	13.9k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.9k	}
221	2.02k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.09k	{
223		/* src[0] <= src[2] < src[1] */
224	1.09k	ELEMENT t = src[1];
225	1.09k	src[1] = src[2];
226	1.09k	src[2] = t;
227	1.09k	}
228	930	else
229	930	{
230		/* src[2] < src[0] <= src[1] */
231	930	ELEMENT t = src[0];
232	930	src[0] = src[2];
233	930	src[2] = src[1];
234	930	src[1] = t;
235	930	}
236	13.9k	}
237	3.53k	else
238	3.53k	{
239	3.53k	if (COMPARE (&src[0], &src[2]) <= 0)
240	990	{
241		/* src[1] < src[0] <= src[2] */
242	990	ELEMENT t = src[0];
243	990	src[0] = src[1];
244	990	src[1] = t;
245	990	}
246	2.54k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.44k	{
248		/* src[1] <= src[2] < src[0] */
249	1.44k	ELEMENT t = src[0];
250	1.44k	src[0] = src[1];
251	1.44k	src[1] = src[2];
252	1.44k	src[2] = t;
253	1.44k	}
254	1.10k	else
255	1.10k	{
256		/* src[2] < src[1] < src[0] */
257	1.10k	ELEMENT t = src[0];
258	1.10k	src[0] = src[2];
259	1.10k	src[2] = t;
260	1.10k	}
261	3.53k	}
262	17.5k	break;
263	21.0k	default:
264	21.0k	{
265	21.0k	size_t n1 = n / 2;
266	21.0k	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	21.0k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	21.0k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	21.0k	merge (tmp, n1, src + n1, n2, src);
274	21.0k	}
275	21.0k	break;
276	1.46M	}
277	1.46M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC