/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: 2026-07-10 06:45

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	650k	{
49	650k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.96M	{
51	9.96M	if (COMPARE (src1, src2) <= 0)
52	8.88M	{
53	8.88M	dst++ = src1++;
54	8.88M	n1--;
55	8.88M	if (n1 == 0)
56	645k	break;
57	8.88M	}
58	1.08M	else
59	1.08M	{
60	1.08M	dst++ = src2++;
61	1.08M	n2--;
62	1.08M	if (n2 == 0)
63	5.52k	break;
64	1.08M	}
65	9.96M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	650k	if (n1 > 0)
68	5.52k	{
69	5.52k	if (dst != src1)
70	5.52k	do
71	15.7k	{
72	15.7k	dst++ = src1++;
73	15.7k	n1--;
74	15.7k	}
75	15.7k	while (n1 > 0);
76	5.52k	}
77	645k	else /* n2 > 0 */
78	645k	{
79	645k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	645k	}
87	650k	}
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	1.28M	{
100	1.28M	switch (n)
101	1.28M	{
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	592k	case 2:
109		/* Trivial case. */
110	592k	if (COMPARE (&src[0], &src[1]) <= 0)
111	589k	{
112		/* src[0] <= src[1] */
113	589k	dst[0] = src[0];
114	589k	dst[1] = src[1];
115	589k	}
116	2.86k	else
117	2.86k	{
118	2.86k	dst[0] = src[1];
119	2.86k	dst[1] = src[0];
120	2.86k	}
121	592k	break;
122	58.2k	case 3:
123		/* Simple case. */
124	58.2k	if (COMPARE (&src[0], &src[1]) <= 0)
125	54.6k	{
126	54.6k	if (COMPARE (&src[1], &src[2]) <= 0)
127	51.3k	{
128		/* src[0] <= src[1] <= src[2] */
129	51.3k	dst[0] = src[0];
130	51.3k	dst[1] = src[1];
131	51.3k	dst[2] = src[2];
132	51.3k	}
133	3.30k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.15k	{
135		/* src[0] <= src[2] < src[1] */
136	2.15k	dst[0] = src[0];
137	2.15k	dst[1] = src[2];
138	2.15k	dst[2] = src[1];
139	2.15k	}
140	1.15k	else
141	1.15k	{
142		/* src[2] < src[0] <= src[1] */
143	1.15k	dst[0] = src[2];
144	1.15k	dst[1] = src[0];
145	1.15k	dst[2] = src[1];
146	1.15k	}
147	54.6k	}
148	3.59k	else
149	3.59k	{
150	3.59k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.81k	{
152		/* src[1] < src[0] <= src[2] */
153	1.81k	dst[0] = src[1];
154	1.81k	dst[1] = src[0];
155	1.81k	dst[2] = src[2];
156	1.81k	}
157	1.78k	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	590	else
165	590	{
166		/* src[2] < src[1] < src[0] */
167	590	dst[0] = src[2];
168	590	dst[1] = src[1];
169	590	dst[2] = src[0];
170	590	}
171	3.59k	}
172	58.2k	break;
173	637k	default:
174	637k	{
175	637k	size_t n1 = n / 2;
176	637k	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	637k	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	637k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	637k	merge (tmp, n1, dst + n1, n2, dst);
184	637k	}
185	637k	break;
186	1.28M	}
187	1.28M	}
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	1.65M	{
194	1.65M	switch (n)
195	1.65M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.63M	case 2:
201		/* Trivial case. */
202	1.63M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.63M	{
204		/* src[0] <= src[1] */
205	1.63M	}
206	986	else
207	986	{
208	986	ELEMENT t = src[0];
209	986	src[0] = src[1];
210	986	src[1] = t;
211	986	}
212	1.63M	break;
213	6.79k	case 3:
214		/* Simple case. */
215	6.79k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.30k	{
217	4.30k	if (COMPARE (&src[1], &src[2]) <= 0)
218	2.47k	{
219		/* src[0] <= src[1] <= src[2] */
220	2.47k	}
221	1.82k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	932	{
223		/* src[0] <= src[2] < src[1] */
224	932	ELEMENT t = src[1];
225	932	src[1] = src[2];
226	932	src[2] = t;
227	932	}
228	894	else
229	894	{
230		/* src[2] < src[0] <= src[1] */
231	894	ELEMENT t = src[0];
232	894	src[0] = src[2];
233	894	src[2] = src[1];
234	894	src[1] = t;
235	894	}
236	4.30k	}
237	2.49k	else
238	2.49k	{
239	2.49k	if (COMPARE (&src[0], &src[2]) <= 0)
240	924	{
241		/* src[1] < src[0] <= src[2] */
242	924	ELEMENT t = src[0];
243	924	src[0] = src[1];
244	924	src[1] = t;
245	924	}
246	1.57k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	886	{
248		/* src[1] <= src[2] < src[0] */
249	886	ELEMENT t = src[0];
250	886	src[0] = src[1];
251	886	src[1] = src[2];
252	886	src[2] = t;
253	886	}
254	684	else
255	684	{
256		/* src[2] < src[1] < src[0] */
257	684	ELEMENT t = src[0];
258	684	src[0] = src[2];
259	684	src[2] = t;
260	684	}
261	2.49k	}
262	6.79k	break;
263	13.4k	default:
264	13.4k	{
265	13.4k	size_t n1 = n / 2;
266	13.4k	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	13.4k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	13.4k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	13.4k	merge (tmp, n1, src + n1, n2, src);
274	13.4k	}
275	13.4k	break;
276	1.65M	}
277	1.65M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC