/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: 2026-04-11 06:41

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	764k	{
49	764k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	11.4M	{
51	11.4M	if (COMPARE (src1, src2) <= 0)
52	10.1M	{
53	10.1M	dst++ = src1++;
54	10.1M	n1--;
55	10.1M	if (n1 == 0)
56	757k	break;
57	10.1M	}
58	1.31M	else
59	1.31M	{
60	1.31M	dst++ = src2++;
61	1.31M	n2--;
62	1.31M	if (n2 == 0)
63	6.61k	break;
64	1.31M	}
65	11.4M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	764k	if (n1 > 0)
68	6.61k	{
69	6.61k	if (dst != src1)
70	6.61k	do
71	19.4k	{
72	19.4k	dst++ = src1++;
73	19.4k	n1--;
74	19.4k	}
75	19.4k	while (n1 > 0);
76	6.61k	}
77	757k	else /* n2 > 0 */
78	757k	{
79	757k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	757k	}
87	764k	}
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	1.50M	{
100	1.50M	switch (n)
101	1.50M	{
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	688k	case 2:
109		/* Trivial case. */
110	688k	if (COMPARE (&src[0], &src[1]) <= 0)
111	685k	{
112		/* src[0] <= src[1] */
113	685k	dst[0] = src[0];
114	685k	dst[1] = src[1];
115	685k	}
116	2.64k	else
117	2.64k	{
118	2.64k	dst[0] = src[1];
119	2.64k	dst[1] = src[0];
120	2.64k	}
121	688k	break;
122	75.5k	case 3:
123		/* Simple case. */
124	75.5k	if (COMPARE (&src[0], &src[1]) <= 0)
125	72.1k	{
126	72.1k	if (COMPARE (&src[1], &src[2]) <= 0)
127	68.9k	{
128		/* src[0] <= src[1] <= src[2] */
129	68.9k	dst[0] = src[0];
130	68.9k	dst[1] = src[1];
131	68.9k	dst[2] = src[2];
132	68.9k	}
133	3.22k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.12k	{
135		/* src[0] <= src[2] < src[1] */
136	2.12k	dst[0] = src[0];
137	2.12k	dst[1] = src[2];
138	2.12k	dst[2] = src[1];
139	2.12k	}
140	1.09k	else
141	1.09k	{
142		/* src[2] < src[0] <= src[1] */
143	1.09k	dst[0] = src[2];
144	1.09k	dst[1] = src[0];
145	1.09k	dst[2] = src[1];
146	1.09k	}
147	72.1k	}
148	3.36k	else
149	3.36k	{
150	3.36k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.34k	{
152		/* src[1] < src[0] <= src[2] */
153	1.34k	dst[0] = src[1];
154	1.34k	dst[1] = src[0];
155	1.34k	dst[2] = src[2];
156	1.34k	}
157	2.01k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.19k	{
159		/* src[1] <= src[2] < src[0] */
160	1.19k	dst[0] = src[1];
161	1.19k	dst[1] = src[2];
162	1.19k	dst[2] = src[0];
163	1.19k	}
164	827	else
165	827	{
166		/* src[2] < src[1] < src[0] */
167	827	dst[0] = src[2];
168	827	dst[1] = src[1];
169	827	dst[2] = src[0];
170	827	}
171	3.36k	}
172	75.5k	break;
173	740k	default:
174	740k	{
175	740k	size_t n1 = n / 2;
176	740k	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	740k	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	740k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	740k	merge (tmp, n1, dst + n1, n2, dst);
184	740k	}
185	740k	break;
186	1.50M	}
187	1.50M	}
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	1.64M	{
194	1.64M	switch (n)
195	1.64M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.60M	case 2:
201		/* Trivial case. */
202	1.60M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.60M	{
204		/* src[0] <= src[1] */
205	1.60M	}
206	1.12k	else
207	1.12k	{
208	1.12k	ELEMENT t = src[0];
209	1.12k	src[0] = src[1];
210	1.12k	src[1] = t;
211	1.12k	}
212	1.60M	break;
213	17.9k	case 3:
214		/* Simple case. */
215	17.9k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.9k	{
217	13.9k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.5k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.5k	}
221	2.40k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.33k	{
223		/* src[0] <= src[2] < src[1] */
224	1.33k	ELEMENT t = src[1];
225	1.33k	src[1] = src[2];
226	1.33k	src[2] = t;
227	1.33k	}
228	1.07k	else
229	1.07k	{
230		/* src[2] < src[0] <= src[1] */
231	1.07k	ELEMENT t = src[0];
232	1.07k	src[0] = src[2];
233	1.07k	src[2] = src[1];
234	1.07k	src[1] = t;
235	1.07k	}
236	13.9k	}
237	3.92k	else
238	3.92k	{
239	3.92k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.40k	{
241		/* src[1] < src[0] <= src[2] */
242	1.40k	ELEMENT t = src[0];
243	1.40k	src[0] = src[1];
244	1.40k	src[1] = t;
245	1.40k	}
246	2.51k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.43k	{
248		/* src[1] <= src[2] < src[0] */
249	1.43k	ELEMENT t = src[0];
250	1.43k	src[0] = src[1];
251	1.43k	src[1] = src[2];
252	1.43k	src[2] = t;
253	1.43k	}
254	1.08k	else
255	1.08k	{
256		/* src[2] < src[1] < src[0] */
257	1.08k	ELEMENT t = src[0];
258	1.08k	src[0] = src[2];
259	1.08k	src[2] = t;
260	1.08k	}
261	3.92k	}
262	17.9k	break;
263	23.7k	default:
264	23.7k	{
265	23.7k	size_t n1 = n / 2;
266	23.7k	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	23.7k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	23.7k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	23.7k	merge (tmp, n1, src + n1, n2, src);
274	23.7k	}
275	23.7k	break;
276	1.64M	}
277	1.64M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC