/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: 2026-01-31 06:23

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	68.7k	{
49	68.7k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	399k	{
51	399k	if (COMPARE (src1, src2) <= 0)
52	345k	{
53	345k	dst++ = src1++;
54	345k	n1--;
55	345k	if (n1 == 0)
56	65.0k	break;
57	345k	}
58	54.1k	else
59	54.1k	{
60	54.1k	dst++ = src2++;
61	54.1k	n2--;
62	54.1k	if (n2 == 0)
63	3.68k	break;
64	54.1k	}
65	399k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	68.7k	if (n1 > 0)
68	3.68k	{
69	3.68k	if (dst != src1)
70	3.68k	do
71	5.92k	{
72	5.92k	dst++ = src1++;
73	5.92k	n1--;
74	5.92k	}
75	5.92k	while (n1 > 0);
76	3.68k	}
77	65.0k	else /* n2 > 0 */
78	65.0k	{
79	65.0k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	65.0k	}
87	68.7k	}
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	118k	{
100	118k	switch (n)
101	118k	{
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	58.9k	case 2:
109		/* Trivial case. */
110	58.9k	if (COMPARE (&src[0], &src[1]) <= 0)
111	54.9k	{
112		/* src[0] <= src[1] */
113	54.9k	dst[0] = src[0];
114	54.9k	dst[1] = src[1];
115	54.9k	}
116	3.96k	else
117	3.96k	{
118	3.96k	dst[0] = src[1];
119	3.96k	dst[1] = src[0];
120	3.96k	}
121	58.9k	break;
122	9.85k	case 3:
123		/* Simple case. */
124	9.85k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.46k	{
126	7.46k	if (COMPARE (&src[1], &src[2]) <= 0)
127	5.34k	{
128		/* src[0] <= src[1] <= src[2] */
129	5.34k	dst[0] = src[0];
130	5.34k	dst[1] = src[1];
131	5.34k	dst[2] = src[2];
132	5.34k	}
133	2.11k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.31k	{
135		/* src[0] <= src[2] < src[1] */
136	1.31k	dst[0] = src[0];
137	1.31k	dst[1] = src[2];
138	1.31k	dst[2] = src[1];
139	1.31k	}
140	799	else
141	799	{
142		/* src[2] < src[0] <= src[1] */
143	799	dst[0] = src[2];
144	799	dst[1] = src[0];
145	799	dst[2] = src[1];
146	799	}
147	7.46k	}
148	2.39k	else
149	2.39k	{
150	2.39k	if (COMPARE (&src[0], &src[2]) <= 0)
151	958	{
152		/* src[1] < src[0] <= src[2] */
153	958	dst[0] = src[1];
154	958	dst[1] = src[0];
155	958	dst[2] = src[2];
156	958	}
157	1.43k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	770	{
159		/* src[1] <= src[2] < src[0] */
160	770	dst[0] = src[1];
161	770	dst[1] = src[2];
162	770	dst[2] = src[0];
163	770	}
164	664	else
165	664	{
166		/* src[2] < src[1] < src[0] */
167	664	dst[0] = src[2];
168	664	dst[1] = src[1];
169	664	dst[2] = src[0];
170	664	}
171	2.39k	}
172	9.85k	break;
173	49.3k	default:
174	49.3k	{
175	49.3k	size_t n1 = n / 2;
176	49.3k	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	49.3k	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	49.3k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	49.3k	merge (tmp, n1, dst + n1, n2, dst);
184	49.3k	}
185	49.3k	break;
186	118k	}
187	118k	}
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	100k	{
194	100k	switch (n)
195	100k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	85.0k	case 2:
201		/* Trivial case. */
202	85.0k	if (COMPARE (&src[0], &src[1]) <= 0)
203	84.3k	{
204		/* src[0] <= src[1] */
205	84.3k	}
206	667	else
207	667	{
208	667	ELEMENT t = src[0];
209	667	src[0] = src[1];
210	667	src[1] = t;
211	667	}
212	85.0k	break;
213	5.89k	case 3:
214		/* Simple case. */
215	5.89k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.19k	{
217	4.19k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.04k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.04k	}
221	1.14k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	616	{
223		/* src[0] <= src[2] < src[1] */
224	616	ELEMENT t = src[1];
225	616	src[1] = src[2];
226	616	src[2] = t;
227	616	}
228	529	else
229	529	{
230		/* src[2] < src[0] <= src[1] */
231	529	ELEMENT t = src[0];
232	529	src[0] = src[2];
233	529	src[2] = src[1];
234	529	src[1] = t;
235	529	}
236	4.19k	}
237	1.70k	else
238	1.70k	{
239	1.70k	if (COMPARE (&src[0], &src[2]) <= 0)
240	690	{
241		/* src[1] < src[0] <= src[2] */
242	690	ELEMENT t = src[0];
243	690	src[0] = src[1];
244	690	src[1] = t;
245	690	}
246	1.01k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	553	{
248		/* src[1] <= src[2] < src[0] */
249	553	ELEMENT t = src[0];
250	553	src[0] = src[1];
251	553	src[1] = src[2];
252	553	src[2] = t;
253	553	}
254	459	else
255	459	{
256		/* src[2] < src[1] < src[0] */
257	459	ELEMENT t = src[0];
258	459	src[0] = src[2];
259	459	src[2] = t;
260	459	}
261	1.70k	}
262	5.89k	break;
263	10.0k	default:
264	10.0k	{
265	10.0k	size_t n1 = n / 2;
266	10.0k	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	10.0k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	10.0k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	10.0k	merge (tmp, n1, src + n1, n2, src);
274	10.0k	}
275	10.0k	break;
276	100k	}
277	100k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC