/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: 2026-04-06 06:30

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	716k	{
49	716k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.7M	{
51	10.7M	if (COMPARE (src1, src2) <= 0)
52	9.43M	{
53	9.43M	dst++ = src1++;
54	9.43M	n1--;
55	9.43M	if (n1 == 0)
56	710k	break;
57	9.43M	}
58	1.27M	else
59	1.27M	{
60	1.27M	dst++ = src2++;
61	1.27M	n2--;
62	1.27M	if (n2 == 0)
63	6.17k	break;
64	1.27M	}
65	10.7M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	716k	if (n1 > 0)
68	6.17k	{
69	6.17k	if (dst != src1)
70	6.17k	do
71	23.6k	{
72	23.6k	dst++ = src1++;
73	23.6k	n1--;
74	23.6k	}
75	23.6k	while (n1 > 0);
76	6.17k	}
77	710k	else /* n2 > 0 */
78	710k	{
79	710k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	710k	}
87	716k	}
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	1.41M	{
100	1.41M	switch (n)
101	1.41M	{
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	643k	case 2:
109		/* Trivial case. */
110	643k	if (COMPARE (&src[0], &src[1]) <= 0)
111	640k	{
112		/* src[0] <= src[1] */
113	640k	dst[0] = src[0];
114	640k	dst[1] = src[1];
115	640k	}
116	2.74k	else
117	2.74k	{
118	2.74k	dst[0] = src[1];
119	2.74k	dst[1] = src[0];
120	2.74k	}
121	643k	break;
122	73.5k	case 3:
123		/* Simple case. */
124	73.5k	if (COMPARE (&src[0], &src[1]) <= 0)
125	70.0k	{
126	70.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	67.1k	{
128		/* src[0] <= src[1] <= src[2] */
129	67.1k	dst[0] = src[0];
130	67.1k	dst[1] = src[1];
131	67.1k	dst[2] = src[2];
132	67.1k	}
133	2.91k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.87k	{
135		/* src[0] <= src[2] < src[1] */
136	1.87k	dst[0] = src[0];
137	1.87k	dst[1] = src[2];
138	1.87k	dst[2] = src[1];
139	1.87k	}
140	1.04k	else
141	1.04k	{
142		/* src[2] < src[0] <= src[1] */
143	1.04k	dst[0] = src[2];
144	1.04k	dst[1] = src[0];
145	1.04k	dst[2] = src[1];
146	1.04k	}
147	70.0k	}
148	3.47k	else
149	3.47k	{
150	3.47k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.41k	{
152		/* src[1] < src[0] <= src[2] */
153	1.41k	dst[0] = src[1];
154	1.41k	dst[1] = src[0];
155	1.41k	dst[2] = src[2];
156	1.41k	}
157	2.06k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.24k	{
159		/* src[1] <= src[2] < src[0] */
160	1.24k	dst[0] = src[1];
161	1.24k	dst[1] = src[2];
162	1.24k	dst[2] = src[0];
163	1.24k	}
164	821	else
165	821	{
166		/* src[2] < src[1] < src[0] */
167	821	dst[0] = src[2];
168	821	dst[1] = src[1];
169	821	dst[2] = src[0];
170	821	}
171	3.47k	}
172	73.5k	break;
173	694k	default:
174	694k	{
175	694k	size_t n1 = n / 2;
176	694k	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	694k	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	694k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	694k	merge (tmp, n1, dst + n1, n2, dst);
184	694k	}
185	694k	break;
186	1.41M	}
187	1.41M	}
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	1.55M	{
194	1.55M	switch (n)
195	1.55M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.51M	case 2:
201		/* Trivial case. */
202	1.51M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.51M	{
204		/* src[0] <= src[1] */
205	1.51M	}
206	1.00k	else
207	1.00k	{
208	1.00k	ELEMENT t = src[0];
209	1.00k	src[0] = src[1];
210	1.00k	src[1] = t;
211	1.00k	}
212	1.51M	break;
213	16.4k	case 3:
214		/* Simple case. */
215	16.4k	if (COMPARE (&src[0], &src[1]) <= 0)
216	12.8k	{
217	12.8k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.8k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.8k	}
221	1.99k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.07k	{
223		/* src[0] <= src[2] < src[1] */
224	1.07k	ELEMENT t = src[1];
225	1.07k	src[1] = src[2];
226	1.07k	src[2] = t;
227	1.07k	}
228	921	else
229	921	{
230		/* src[2] < src[0] <= src[1] */
231	921	ELEMENT t = src[0];
232	921	src[0] = src[2];
233	921	src[2] = src[1];
234	921	src[1] = t;
235	921	}
236	12.8k	}
237	3.56k	else
238	3.56k	{
239	3.56k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.17k	{
241		/* src[1] < src[0] <= src[2] */
242	1.17k	ELEMENT t = src[0];
243	1.17k	src[0] = src[1];
244	1.17k	src[1] = t;
245	1.17k	}
246	2.39k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.36k	{
248		/* src[1] <= src[2] < src[0] */
249	1.36k	ELEMENT t = src[0];
250	1.36k	src[0] = src[1];
251	1.36k	src[1] = src[2];
252	1.36k	src[2] = t;
253	1.36k	}
254	1.03k	else
255	1.03k	{
256		/* src[2] < src[1] < src[0] */
257	1.03k	ELEMENT t = src[0];
258	1.03k	src[0] = src[2];
259	1.03k	src[2] = t;
260	1.03k	}
261	3.56k	}
262	16.4k	break;
263	22.5k	default:
264	22.5k	{
265	22.5k	size_t n1 = n / 2;
266	22.5k	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	22.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	22.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	22.5k	merge (tmp, n1, src + n1, n2, src);
274	22.5k	}
275	22.5k	break;
276	1.55M	}
277	1.55M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC