/src/libunistring/lib/array-mergesort.h

Source
/* Stable-sorting of an array using mergesort.
   Copyright (C) 2009-2025 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: 2025-12-05 06:16

Line	Count	Source
1		/* Stable-sorting of an array using mergesort.
2		Copyright (C) 2009-2025 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	625k	{
49	625k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.09M	{
51	9.09M	if (COMPARE (src1, src2) <= 0)
52	8.16M	{
53	8.16M	dst++ = src1++;
54	8.16M	n1--;
55	8.16M	if (n1 == 0)
56	619k	break;
57	8.16M	}
58	933k	else
59	933k	{
60	933k	dst++ = src2++;
61	933k	n2--;
62	933k	if (n2 == 0)
63	6.12k	break;
64	933k	}
65	9.09M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	625k	if (n1 > 0)
68	6.12k	{
69	6.12k	if (dst != src1)
70	6.12k	do
71	14.0k	{
72	14.0k	dst++ = src1++;
73	14.0k	n1--;
74	14.0k	}
75	14.0k	while (n1 > 0);
76	6.12k	}
77	619k	else /* n2 > 0 */
78	619k	{
79	619k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	619k	}
87	625k	}
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	1.22M	{
100	1.22M	switch (n)
101	1.22M	{
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	561k	case 2:
109		/* Trivial case. */
110	561k	if (COMPARE (&src[0], &src[1]) <= 0)
111	557k	{
112		/* src[0] <= src[1] */
113	557k	dst[0] = src[0];
114	557k	dst[1] = src[1];
115	557k	}
116	3.27k	else
117	3.27k	{
118	3.27k	dst[0] = src[1];
119	3.27k	dst[1] = src[0];
120	3.27k	}
121	561k	break;
122	64.7k	case 3:
123		/* Simple case. */
124	64.7k	if (COMPARE (&src[0], &src[1]) <= 0)
125	60.0k	{
126	60.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	56.5k	{
128		/* src[0] <= src[1] <= src[2] */
129	56.5k	dst[0] = src[0];
130	56.5k	dst[1] = src[1];
131	56.5k	dst[2] = src[2];
132	56.5k	}
133	3.51k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.96k	{
135		/* src[0] <= src[2] < src[1] */
136	1.96k	dst[0] = src[0];
137	1.96k	dst[1] = src[2];
138	1.96k	dst[2] = src[1];
139	1.96k	}
140	1.54k	else
141	1.54k	{
142		/* src[2] < src[0] <= src[1] */
143	1.54k	dst[0] = src[2];
144	1.54k	dst[1] = src[0];
145	1.54k	dst[2] = src[1];
146	1.54k	}
147	60.0k	}
148	4.72k	else
149	4.72k	{
150	4.72k	if (COMPARE (&src[0], &src[2]) <= 0)
151	2.00k	{
152		/* src[1] < src[0] <= src[2] */
153	2.00k	dst[0] = src[1];
154	2.00k	dst[1] = src[0];
155	2.00k	dst[2] = src[2];
156	2.00k	}
157	2.71k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.93k	{
159		/* src[1] <= src[2] < src[0] */
160	1.93k	dst[0] = src[1];
161	1.93k	dst[1] = src[2];
162	1.93k	dst[2] = src[0];
163	1.93k	}
164	781	else
165	781	{
166		/* src[2] < src[1] < src[0] */
167	781	dst[0] = src[2];
168	781	dst[1] = src[1];
169	781	dst[2] = src[0];
170	781	}
171	4.72k	}
172	64.7k	break;
173	600k	default:
174	600k	{
175	600k	size_t n1 = n / 2;
176	600k	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	600k	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	600k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	600k	merge (tmp, n1, dst + n1, n2, dst);
184	600k	}
185	600k	break;
186	1.22M	}
187	1.22M	}
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	1.65M	{
194	1.65M	switch (n)
195	1.65M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.61M	case 2:
201		/* Trivial case. */
202	1.61M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.61M	{
204		/* src[0] <= src[1] */
205	1.61M	}
206	1.23k	else
207	1.23k	{
208	1.23k	ELEMENT t = src[0];
209	1.23k	src[0] = src[1];
210	1.23k	src[1] = t;
211	1.23k	}
212	1.61M	break;
213	17.8k	case 3:
214		/* Simple case. */
215	17.8k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.6k	{
217	13.6k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.9k	}
221	2.76k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.27k	{
223		/* src[0] <= src[2] < src[1] */
224	1.27k	ELEMENT t = src[1];
225	1.27k	src[1] = src[2];
226	1.27k	src[2] = t;
227	1.27k	}
228	1.48k	else
229	1.48k	{
230		/* src[2] < src[0] <= src[1] */
231	1.48k	ELEMENT t = src[0];
232	1.48k	src[0] = src[2];
233	1.48k	src[2] = src[1];
234	1.48k	src[1] = t;
235	1.48k	}
236	13.6k	}
237	4.10k	else
238	4.10k	{
239	4.10k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.16k	{
241		/* src[1] < src[0] <= src[2] */
242	1.16k	ELEMENT t = src[0];
243	1.16k	src[0] = src[1];
244	1.16k	src[1] = t;
245	1.16k	}
246	2.94k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.83k	{
248		/* src[1] <= src[2] < src[0] */
249	1.83k	ELEMENT t = src[0];
250	1.83k	src[0] = src[1];
251	1.83k	src[1] = src[2];
252	1.83k	src[2] = t;
253	1.83k	}
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	4.10k	}
262	17.8k	break;
263	25.6k	default:
264	25.6k	{
265	25.6k	size_t n1 = n / 2;
266	25.6k	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	25.6k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	25.6k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	25.6k	merge (tmp, n1, src + n1, n2, src);
274	25.6k	}
275	25.6k	break;
276	1.65M	}
277	1.65M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC