/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: 2026-08-22 07:17

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	750k	{
49	750k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	11.1M	{
51	11.1M	if (COMPARE (src1, src2) <= 0)
52	9.88M	{
53	9.88M	dst++ = src1++;
54	9.88M	n1--;
55	9.88M	if (n1 == 0)
56	743k	break;
57	9.88M	}
58	1.29M	else
59	1.29M	{
60	1.29M	dst++ = src2++;
61	1.29M	n2--;
62	1.29M	if (n2 == 0)
63	7.48k	break;
64	1.29M	}
65	11.1M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	750k	if (n1 > 0)
68	7.48k	{
69	7.48k	if (dst != src1)
70	7.48k	do
71	24.1k	{
72	24.1k	dst++ = src1++;
73	24.1k	n1--;
74	24.1k	}
75	24.1k	while (n1 > 0);
76	7.48k	}
77	743k	else /* n2 > 0 */
78	743k	{
79	743k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	743k	}
87	750k	}
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	1.47M	{
100	1.47M	switch (n)
101	1.47M	{
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	670k	case 2:
109		/* Trivial case. */
110	670k	if (COMPARE (&src[0], &src[1]) <= 0)
111	666k	{
112		/* src[0] <= src[1] */
113	666k	dst[0] = src[0];
114	666k	dst[1] = src[1];
115	666k	}
116	4.05k	else
117	4.05k	{
118	4.05k	dst[0] = src[1];
119	4.05k	dst[1] = src[0];
120	4.05k	}
121	670k	break;
122	80.0k	case 3:
123		/* Simple case. */
124	80.0k	if (COMPARE (&src[0], &src[1]) <= 0)
125	75.7k	{
126	75.7k	if (COMPARE (&src[1], &src[2]) <= 0)
127	71.7k	{
128		/* src[0] <= src[1] <= src[2] */
129	71.7k	dst[0] = src[0];
130	71.7k	dst[1] = src[1];
131	71.7k	dst[2] = src[2];
132	71.7k	}
133	3.97k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.58k	{
135		/* src[0] <= src[2] < src[1] */
136	2.58k	dst[0] = src[0];
137	2.58k	dst[1] = src[2];
138	2.58k	dst[2] = src[1];
139	2.58k	}
140	1.39k	else
141	1.39k	{
142		/* src[2] < src[0] <= src[1] */
143	1.39k	dst[0] = src[2];
144	1.39k	dst[1] = src[0];
145	1.39k	dst[2] = src[1];
146	1.39k	}
147	75.7k	}
148	4.35k	else
149	4.35k	{
150	4.35k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.56k	{
152		/* src[1] < src[0] <= src[2] */
153	1.56k	dst[0] = src[1];
154	1.56k	dst[1] = src[0];
155	1.56k	dst[2] = src[2];
156	1.56k	}
157	2.79k	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	855	else
165	855	{
166		/* src[2] < src[1] < src[0] */
167	855	dst[0] = src[2];
168	855	dst[1] = src[1];
169	855	dst[2] = src[0];
170	855	}
171	4.35k	}
172	80.0k	break;
173	726k	default:
174	726k	{
175	726k	size_t n1 = n / 2;
176	726k	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	726k	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	726k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	726k	merge (tmp, n1, dst + n1, n2, dst);
184	726k	}
185	726k	break;
186	1.47M	}
187	1.47M	}
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	1.69M	{
194	1.69M	switch (n)
195	1.69M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.65M	case 2:
201		/* Trivial case. */
202	1.65M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.65M	{
204		/* src[0] <= src[1] */
205	1.65M	}
206	1.29k	else
207	1.29k	{
208	1.29k	ELEMENT t = src[0];
209	1.29k	src[0] = src[1];
210	1.29k	src[1] = t;
211	1.29k	}
212	1.65M	break;
213	18.0k	case 3:
214		/* Simple case. */
215	18.0k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.2k	{
217	14.2k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.6k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.6k	}
221	2.56k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.34k	{
223		/* src[0] <= src[2] < src[1] */
224	1.34k	ELEMENT t = src[1];
225	1.34k	src[1] = src[2];
226	1.34k	src[2] = t;
227	1.34k	}
228	1.22k	else
229	1.22k	{
230		/* src[2] < src[0] <= src[1] */
231	1.22k	ELEMENT t = src[0];
232	1.22k	src[0] = src[2];
233	1.22k	src[2] = src[1];
234	1.22k	src[1] = t;
235	1.22k	}
236	14.2k	}
237	3.83k	else
238	3.83k	{
239	3.83k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.13k	{
241		/* src[1] < src[0] <= src[2] */
242	1.13k	ELEMENT t = src[0];
243	1.13k	src[0] = src[1];
244	1.13k	src[1] = t;
245	1.13k	}
246	2.69k	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	1.24k	else
255	1.24k	{
256		/* src[2] < src[1] < src[0] */
257	1.24k	ELEMENT t = src[0];
258	1.24k	src[0] = src[2];
259	1.24k	src[2] = t;
260	1.24k	}
261	3.83k	}
262	18.0k	break;
263	24.8k	default:
264	24.8k	{
265	24.8k	size_t n1 = n / 2;
266	24.8k	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	24.8k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	24.8k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	24.8k	merge (tmp, n1, src + n1, n2, src);
274	24.8k	}
275	24.8k	break;
276	1.69M	}
277	1.69M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC