/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: 2026-09-01 06:47

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	778k	{
49	778k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	11.2M	{
51	11.2M	if (COMPARE (src1, src2) <= 0)
52	9.97M	{
53	9.97M	dst++ = src1++;
54	9.97M	n1--;
55	9.97M	if (n1 == 0)
56	771k	break;
57	9.97M	}
58	1.25M	else
59	1.25M	{
60	1.25M	dst++ = src2++;
61	1.25M	n2--;
62	1.25M	if (n2 == 0)
63	7.05k	break;
64	1.25M	}
65	11.2M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	778k	if (n1 > 0)
68	7.05k	{
69	7.05k	if (dst != src1)
70	7.05k	do
71	21.1k	{
72	21.1k	dst++ = src1++;
73	21.1k	n1--;
74	21.1k	}
75	21.1k	while (n1 > 0);
76	7.05k	}
77	771k	else /* n2 > 0 */
78	771k	{
79	771k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	771k	}
87	778k	}
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	1.52M	{
100	1.52M	switch (n)
101	1.52M	{
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	699k	case 2:
109		/* Trivial case. */
110	699k	if (COMPARE (&src[0], &src[1]) <= 0)
111	694k	{
112		/* src[0] <= src[1] */
113	694k	dst[0] = src[0];
114	694k	dst[1] = src[1];
115	694k	}
116	4.82k	else
117	4.82k	{
118	4.82k	dst[0] = src[1];
119	4.82k	dst[1] = src[0];
120	4.82k	}
121	699k	break;
122	79.7k	case 3:
123		/* Simple case. */
124	79.7k	if (COMPARE (&src[0], &src[1]) <= 0)
125	72.9k	{
126	72.9k	if (COMPARE (&src[1], &src[2]) <= 0)
127	68.1k	{
128		/* src[0] <= src[1] <= src[2] */
129	68.1k	dst[0] = src[0];
130	68.1k	dst[1] = src[1];
131	68.1k	dst[2] = src[2];
132	68.1k	}
133	4.80k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	3.02k	{
135		/* src[0] <= src[2] < src[1] */
136	3.02k	dst[0] = src[0];
137	3.02k	dst[1] = src[2];
138	3.02k	dst[2] = src[1];
139	3.02k	}
140	1.78k	else
141	1.78k	{
142		/* src[2] < src[0] <= src[1] */
143	1.78k	dst[0] = src[2];
144	1.78k	dst[1] = src[0];
145	1.78k	dst[2] = src[1];
146	1.78k	}
147	72.9k	}
148	6.76k	else
149	6.76k	{
150	6.76k	if (COMPARE (&src[0], &src[2]) <= 0)
151	3.11k	{
152		/* src[1] < src[0] <= src[2] */
153	3.11k	dst[0] = src[1];
154	3.11k	dst[1] = src[0];
155	3.11k	dst[2] = src[2];
156	3.11k	}
157	3.65k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	2.26k	{
159		/* src[1] <= src[2] < src[0] */
160	2.26k	dst[0] = src[1];
161	2.26k	dst[1] = src[2];
162	2.26k	dst[2] = src[0];
163	2.26k	}
164	1.38k	else
165	1.38k	{
166		/* src[2] < src[1] < src[0] */
167	1.38k	dst[0] = src[2];
168	1.38k	dst[1] = src[1];
169	1.38k	dst[2] = src[0];
170	1.38k	}
171	6.76k	}
172	79.7k	break;
173	741k	default:
174	741k	{
175	741k	size_t n1 = n / 2;
176	741k	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	741k	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	741k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	741k	merge (tmp, n1, dst + n1, n2, dst);
184	741k	}
185	741k	break;
186	1.52M	}
187	1.52M	}
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	1.72M	{
194	1.72M	switch (n)
195	1.72M	{
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	2.21k	else
207	2.21k	{
208	2.21k	ELEMENT t = src[0];
209	2.21k	src[0] = src[1];
210	2.21k	src[1] = t;
211	2.21k	}
212	1.65M	break;
213	22.9k	case 3:
214		/* Simple case. */
215	22.9k	if (COMPARE (&src[0], &src[1]) <= 0)
216	18.7k	{
217	18.7k	if (COMPARE (&src[1], &src[2]) <= 0)
218	16.1k	{
219		/* src[0] <= src[1] <= src[2] */
220	16.1k	}
221	2.57k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.22k	{
223		/* src[0] <= src[2] < src[1] */
224	1.22k	ELEMENT t = src[1];
225	1.22k	src[1] = src[2];
226	1.22k	src[2] = t;
227	1.22k	}
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	18.7k	}
237	4.20k	else
238	4.20k	{
239	4.20k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.62k	{
241		/* src[1] < src[0] <= src[2] */
242	1.62k	ELEMENT t = src[0];
243	1.62k	src[0] = src[1];
244	1.62k	src[1] = t;
245	1.62k	}
246	2.58k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.52k	{
248		/* src[1] <= src[2] < src[0] */
249	1.52k	ELEMENT t = src[0];
250	1.52k	src[0] = src[1];
251	1.52k	src[1] = src[2];
252	1.52k	src[2] = t;
253	1.52k	}
254	1.06k	else
255	1.06k	{
256		/* src[2] < src[1] < src[0] */
257	1.06k	ELEMENT t = src[0];
258	1.06k	src[0] = src[2];
259	1.06k	src[2] = t;
260	1.06k	}
261	4.20k	}
262	22.9k	break;
263	37.5k	default:
264	37.5k	{
265	37.5k	size_t n1 = n / 2;
266	37.5k	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	37.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	37.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	37.5k	merge (tmp, n1, src + n1, n2, src);
274	37.5k	}
275	37.5k	break;
276	1.72M	}
277	1.72M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC