/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: 2026-05-23 06:35

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	721k	{
49	721k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.8M	{
51	10.8M	if (COMPARE (src1, src2) <= 0)
52	9.58M	{
53	9.58M	dst++ = src1++;
54	9.58M	n1--;
55	9.58M	if (n1 == 0)
56	715k	break;
57	9.58M	}
58	1.22M	else
59	1.22M	{
60	1.22M	dst++ = src2++;
61	1.22M	n2--;
62	1.22M	if (n2 == 0)
63	6.74k	break;
64	1.22M	}
65	10.8M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	721k	if (n1 > 0)
68	6.74k	{
69	6.74k	if (dst != src1)
70	6.74k	do
71	17.8k	{
72	17.8k	dst++ = src1++;
73	17.8k	n1--;
74	17.8k	}
75	17.8k	while (n1 > 0);
76	6.74k	}
77	715k	else /* n2 > 0 */
78	715k	{
79	715k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	715k	}
87	721k	}
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	1.42M	{
100	1.42M	switch (n)
101	1.42M	{
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	647k	case 2:
109		/* Trivial case. */
110	647k	if (COMPARE (&src[0], &src[1]) <= 0)
111	645k	{
112		/* src[0] <= src[1] */
113	645k	dst[0] = src[0];
114	645k	dst[1] = src[1];
115	645k	}
116	2.81k	else
117	2.81k	{
118	2.81k	dst[0] = src[1];
119	2.81k	dst[1] = src[0];
120	2.81k	}
121	647k	break;
122	73.8k	case 3:
123		/* Simple case. */
124	73.8k	if (COMPARE (&src[0], &src[1]) <= 0)
125	70.2k	{
126	70.2k	if (COMPARE (&src[1], &src[2]) <= 0)
127	66.4k	{
128		/* src[0] <= src[1] <= src[2] */
129	66.4k	dst[0] = src[0];
130	66.4k	dst[1] = src[1];
131	66.4k	dst[2] = src[2];
132	66.4k	}
133	3.73k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.51k	{
135		/* src[0] <= src[2] < src[1] */
136	2.51k	dst[0] = src[0];
137	2.51k	dst[1] = src[2];
138	2.51k	dst[2] = src[1];
139	2.51k	}
140	1.22k	else
141	1.22k	{
142		/* src[2] < src[0] <= src[1] */
143	1.22k	dst[0] = src[2];
144	1.22k	dst[1] = src[0];
145	1.22k	dst[2] = src[1];
146	1.22k	}
147	70.2k	}
148	3.63k	else
149	3.63k	{
150	3.63k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.68k	{
152		/* src[1] < src[0] <= src[2] */
153	1.68k	dst[0] = src[1];
154	1.68k	dst[1] = src[0];
155	1.68k	dst[2] = src[2];
156	1.68k	}
157	1.94k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.08k	{
159		/* src[1] <= src[2] < src[0] */
160	1.08k	dst[0] = src[1];
161	1.08k	dst[1] = src[2];
162	1.08k	dst[2] = src[0];
163	1.08k	}
164	864	else
165	864	{
166		/* src[2] < src[1] < src[0] */
167	864	dst[0] = src[2];
168	864	dst[1] = src[1];
169	864	dst[2] = src[0];
170	864	}
171	3.63k	}
172	73.8k	break;
173	698k	default:
174	698k	{
175	698k	size_t n1 = n / 2;
176	698k	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	698k	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	698k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	698k	merge (tmp, n1, dst + n1, n2, dst);
184	698k	}
185	698k	break;
186	1.42M	}
187	1.42M	}
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	1.49M	{
194	1.49M	switch (n)
195	1.49M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.45M	case 2:
201		/* Trivial case. */
202	1.45M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.45M	{
204		/* src[0] <= src[1] */
205	1.45M	}
206	1.09k	else
207	1.09k	{
208	1.09k	ELEMENT t = src[0];
209	1.09k	src[0] = src[1];
210	1.09k	src[1] = t;
211	1.09k	}
212	1.45M	break;
213	17.7k	case 3:
214		/* Simple case. */
215	17.7k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.1k	{
217	14.1k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.8k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.8k	}
221	2.33k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.33k	{
223		/* src[0] <= src[2] < src[1] */
224	1.33k	ELEMENT t = src[1];
225	1.33k	src[1] = src[2];
226	1.33k	src[2] = t;
227	1.33k	}
228	1.00k	else
229	1.00k	{
230		/* src[2] < src[0] <= src[1] */
231	1.00k	ELEMENT t = src[0];
232	1.00k	src[0] = src[2];
233	1.00k	src[2] = src[1];
234	1.00k	src[1] = t;
235	1.00k	}
236	14.1k	}
237	3.59k	else
238	3.59k	{
239	3.59k	if (COMPARE (&src[0], &src[2]) <= 0)
240	976	{
241		/* src[1] < src[0] <= src[2] */
242	976	ELEMENT t = src[0];
243	976	src[0] = src[1];
244	976	src[1] = t;
245	976	}
246	2.61k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.45k	{
248		/* src[1] <= src[2] < src[0] */
249	1.45k	ELEMENT t = src[0];
250	1.45k	src[0] = src[1];
251	1.45k	src[1] = src[2];
252	1.45k	src[2] = t;
253	1.45k	}
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	3.59k	}
262	17.7k	break;
263	23.3k	default:
264	23.3k	{
265	23.3k	size_t n1 = n / 2;
266	23.3k	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	23.3k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	23.3k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	23.3k	merge (tmp, n1, src + n1, n2, src);
274	23.3k	}
275	23.3k	break;
276	1.49M	}
277	1.49M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC