/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: 2025-11-05 06:28

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	630k	{
49	630k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.17M	{
51	9.17M	if (COMPARE (src1, src2) <= 0)
52	8.25M	{
53	8.25M	dst++ = src1++;
54	8.25M	n1--;
55	8.25M	if (n1 == 0)
56	625k	break;
57	8.25M	}
58	925k	else
59	925k	{
60	925k	dst++ = src2++;
61	925k	n2--;
62	925k	if (n2 == 0)
63	5.59k	break;
64	925k	}
65	9.17M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	630k	if (n1 > 0)
68	5.59k	{
69	5.59k	if (dst != src1)
70	5.59k	do
71	16.7k	{
72	16.7k	dst++ = src1++;
73	16.7k	n1--;
74	16.7k	}
75	16.7k	while (n1 > 0);
76	5.59k	}
77	625k	else /* n2 > 0 */
78	625k	{
79	625k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	625k	}
87	630k	}
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	1.23M	{
100	1.23M	switch (n)
101	1.23M	{
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	571k	case 2:
109		/* Trivial case. */
110	571k	if (COMPARE (&src[0], &src[1]) <= 0)
111	567k	{
112		/* src[0] <= src[1] */
113	567k	dst[0] = src[0];
114	567k	dst[1] = src[1];
115	567k	}
116	3.15k	else
117	3.15k	{
118	3.15k	dst[0] = src[1];
119	3.15k	dst[1] = src[0];
120	3.15k	}
121	571k	break;
122	59.6k	case 3:
123		/* Simple case. */
124	59.6k	if (COMPARE (&src[0], &src[1]) <= 0)
125	55.6k	{
126	55.6k	if (COMPARE (&src[1], &src[2]) <= 0)
127	52.6k	{
128		/* src[0] <= src[1] <= src[2] */
129	52.6k	dst[0] = src[0];
130	52.6k	dst[1] = src[1];
131	52.6k	dst[2] = src[2];
132	52.6k	}
133	3.05k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.76k	{
135		/* src[0] <= src[2] < src[1] */
136	1.76k	dst[0] = src[0];
137	1.76k	dst[1] = src[2];
138	1.76k	dst[2] = src[1];
139	1.76k	}
140	1.29k	else
141	1.29k	{
142		/* src[2] < src[0] <= src[1] */
143	1.29k	dst[0] = src[2];
144	1.29k	dst[1] = src[0];
145	1.29k	dst[2] = src[1];
146	1.29k	}
147	55.6k	}
148	4.00k	else
149	4.00k	{
150	4.00k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.69k	{
152		/* src[1] < src[0] <= src[2] */
153	1.69k	dst[0] = src[1];
154	1.69k	dst[1] = src[0];
155	1.69k	dst[2] = src[2];
156	1.69k	}
157	2.30k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.45k	{
159		/* src[1] <= src[2] < src[0] */
160	1.45k	dst[0] = src[1];
161	1.45k	dst[1] = src[2];
162	1.45k	dst[2] = src[0];
163	1.45k	}
164	854	else
165	854	{
166		/* src[2] < src[1] < src[0] */
167	854	dst[0] = src[2];
168	854	dst[1] = src[1];
169	854	dst[2] = src[0];
170	854	}
171	4.00k	}
172	59.6k	break;
173	605k	default:
174	605k	{
175	605k	size_t n1 = n / 2;
176	605k	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	605k	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	605k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	605k	merge (tmp, n1, dst + n1, n2, dst);
184	605k	}
185	605k	break;
186	1.23M	}
187	1.23M	}
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	1.51M	{
194	1.51M	switch (n)
195	1.51M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.46M	case 2:
201		/* Trivial case. */
202	1.46M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.46M	{
204		/* src[0] <= src[1] */
205	1.46M	}
206	1.20k	else
207	1.20k	{
208	1.20k	ELEMENT t = src[0];
209	1.20k	src[0] = src[1];
210	1.20k	src[1] = t;
211	1.20k	}
212	1.46M	break;
213	17.4k	case 3:
214		/* Simple case. */
215	17.4k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.6k	{
217	13.6k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.9k	}
221	2.69k	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	1.34k	else
229	1.34k	{
230		/* src[2] < src[0] <= src[1] */
231	1.34k	ELEMENT t = src[0];
232	1.34k	src[0] = src[2];
233	1.34k	src[2] = src[1];
234	1.34k	src[1] = t;
235	1.34k	}
236	13.6k	}
237	3.82k	else
238	3.82k	{
239	3.82k	if (COMPARE (&src[0], &src[2]) <= 0)
240	971	{
241		/* src[1] < src[0] <= src[2] */
242	971	ELEMENT t = src[0];
243	971	src[0] = src[1];
244	971	src[1] = t;
245	971	}
246	2.84k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.64k	{
248		/* src[1] <= src[2] < src[0] */
249	1.64k	ELEMENT t = src[0];
250	1.64k	src[0] = src[1];
251	1.64k	src[1] = src[2];
252	1.64k	src[2] = t;
253	1.64k	}
254	1.20k	else
255	1.20k	{
256		/* src[2] < src[1] < src[0] */
257	1.20k	ELEMENT t = src[0];
258	1.20k	src[0] = src[2];
259	1.20k	src[2] = t;
260	1.20k	}
261	3.82k	}
262	17.4k	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	1.51M	}
277	1.51M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC