/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: 2026-08-12 07:22

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	746k	{
49	746k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.9M	{
51	10.9M	if (COMPARE (src1, src2) <= 0)
52	9.76M	{
53	9.76M	dst++ = src1++;
54	9.76M	n1--;
55	9.76M	if (n1 == 0)
56	739k	break;
57	9.76M	}
58	1.22M	else
59	1.22M	{
60	1.22M	dst++ = src2++;
61	1.22M	n2--;
62	1.22M	if (n2 == 0)
63	6.67k	break;
64	1.22M	}
65	10.9M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	746k	if (n1 > 0)
68	6.67k	{
69	6.67k	if (dst != src1)
70	6.67k	do
71	20.3k	{
72	20.3k	dst++ = src1++;
73	20.3k	n1--;
74	20.3k	}
75	20.3k	while (n1 > 0);
76	6.67k	}
77	739k	else /* n2 > 0 */
78	739k	{
79	739k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	739k	}
87	746k	}
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	1.46M	{
100	1.46M	switch (n)
101	1.46M	{
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	676k	case 2:
109		/* Trivial case. */
110	676k	if (COMPARE (&src[0], &src[1]) <= 0)
111	673k	{
112		/* src[0] <= src[1] */
113	673k	dst[0] = src[0];
114	673k	dst[1] = src[1];
115	673k	}
116	3.81k	else
117	3.81k	{
118	3.81k	dst[0] = src[1];
119	3.81k	dst[1] = src[0];
120	3.81k	}
121	676k	break;
122	69.1k	case 3:
123		/* Simple case. */
124	69.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	64.9k	{
126	64.9k	if (COMPARE (&src[1], &src[2]) <= 0)
127	61.3k	{
128		/* src[0] <= src[1] <= src[2] */
129	61.3k	dst[0] = src[0];
130	61.3k	dst[1] = src[1];
131	61.3k	dst[2] = src[2];
132	61.3k	}
133	3.63k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.31k	{
135		/* src[0] <= src[2] < src[1] */
136	2.31k	dst[0] = src[0];
137	2.31k	dst[1] = src[2];
138	2.31k	dst[2] = src[1];
139	2.31k	}
140	1.32k	else
141	1.32k	{
142		/* src[2] < src[0] <= src[1] */
143	1.32k	dst[0] = src[2];
144	1.32k	dst[1] = src[0];
145	1.32k	dst[2] = src[1];
146	1.32k	}
147	64.9k	}
148	4.23k	else
149	4.23k	{
150	4.23k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.91k	{
152		/* src[1] < src[0] <= src[2] */
153	1.91k	dst[0] = src[1];
154	1.91k	dst[1] = src[0];
155	1.91k	dst[2] = src[2];
156	1.91k	}
157	2.32k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.52k	{
159		/* src[1] <= src[2] < src[0] */
160	1.52k	dst[0] = src[1];
161	1.52k	dst[1] = src[2];
162	1.52k	dst[2] = src[0];
163	1.52k	}
164	791	else
165	791	{
166		/* src[2] < src[1] < src[0] */
167	791	dst[0] = src[2];
168	791	dst[1] = src[1];
169	791	dst[2] = src[0];
170	791	}
171	4.23k	}
172	69.1k	break;
173	719k	default:
174	719k	{
175	719k	size_t n1 = n / 2;
176	719k	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	719k	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	719k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	719k	merge (tmp, n1, dst + n1, n2, dst);
184	719k	}
185	719k	break;
186	1.46M	}
187	1.46M	}
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	1.71M	{
194	1.71M	switch (n)
195	1.71M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.67M	case 2:
201		/* Trivial case. */
202	1.67M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.66M	{
204		/* src[0] <= src[1] */
205	1.66M	}
206	1.51k	else
207	1.51k	{
208	1.51k	ELEMENT t = src[0];
209	1.51k	src[0] = src[1];
210	1.51k	src[1] = t;
211	1.51k	}
212	1.67M	break;
213	17.2k	case 3:
214		/* Simple case. */
215	17.2k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.3k	{
217	13.3k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.9k	}
221	2.31k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.21k	{
223		/* src[0] <= src[2] < src[1] */
224	1.21k	ELEMENT t = src[1];
225	1.21k	src[1] = src[2];
226	1.21k	src[2] = t;
227	1.21k	}
228	1.10k	else
229	1.10k	{
230		/* src[2] < src[0] <= src[1] */
231	1.10k	ELEMENT t = src[0];
232	1.10k	src[0] = src[2];
233	1.10k	src[2] = src[1];
234	1.10k	src[1] = t;
235	1.10k	}
236	13.3k	}
237	3.91k	else
238	3.91k	{
239	3.91k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.23k	{
241		/* src[1] < src[0] <= src[2] */
242	1.23k	ELEMENT t = src[0];
243	1.23k	src[0] = src[1];
244	1.23k	src[1] = t;
245	1.23k	}
246	2.68k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.59k	{
248		/* src[1] <= src[2] < src[0] */
249	1.59k	ELEMENT t = src[0];
250	1.59k	src[0] = src[1];
251	1.59k	src[1] = src[2];
252	1.59k	src[2] = t;
253	1.59k	}
254	1.09k	else
255	1.09k	{
256		/* src[2] < src[1] < src[0] */
257	1.09k	ELEMENT t = src[0];
258	1.09k	src[0] = src[2];
259	1.09k	src[2] = t;
260	1.09k	}
261	3.91k	}
262	17.2k	break;
263	26.2k	default:
264	26.2k	{
265	26.2k	size_t n1 = n / 2;
266	26.2k	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	26.2k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	26.2k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	26.2k	merge (tmp, n1, src + n1, n2, src);
274	26.2k	}
275	26.2k	break;
276	1.71M	}
277	1.71M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC