/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: 2026-10-16 07:06

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	694k	{
49	694k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.1M	{
51	10.1M	if (COMPARE (src1, src2) <= 0)
52	9.11M	{
53	9.11M	dst++ = src1++;
54	9.11M	n1--;
55	9.11M	if (n1 == 0)
56	688k	break;
57	9.11M	}
58	1.06M	else
59	1.06M	{
60	1.06M	dst++ = src2++;
61	1.06M	n2--;
62	1.06M	if (n2 == 0)
63	6.13k	break;
64	1.06M	}
65	10.1M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	694k	if (n1 > 0)
68	6.13k	{
69	6.13k	if (dst != src1)
70	6.13k	do
71	15.9k	{
72	15.9k	dst++ = src1++;
73	15.9k	n1--;
74	15.9k	}
75	15.9k	while (n1 > 0);
76	6.13k	}
77	688k	else /* n2 > 0 */
78	688k	{
79	688k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	688k	}
87	694k	}
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	1.36M	{
100	1.36M	switch (n)
101	1.36M	{
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	620k	case 2:
109		/* Trivial case. */
110	620k	if (COMPARE (&src[0], &src[1]) <= 0)
111	617k	{
112		/* src[0] <= src[1] */
113	617k	dst[0] = src[0];
114	617k	dst[1] = src[1];
115	617k	}
116	2.80k	else
117	2.80k	{
118	2.80k	dst[0] = src[1];
119	2.80k	dst[1] = src[0];
120	2.80k	}
121	620k	break;
122	74.0k	case 3:
123		/* Simple case. */
124	74.0k	if (COMPARE (&src[0], &src[1]) <= 0)
125	70.4k	{
126	70.4k	if (COMPARE (&src[1], &src[2]) <= 0)
127	67.1k	{
128		/* src[0] <= src[1] <= src[2] */
129	67.1k	dst[0] = src[0];
130	67.1k	dst[1] = src[1];
131	67.1k	dst[2] = src[2];
132	67.1k	}
133	3.30k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.96k	{
135		/* src[0] <= src[2] < src[1] */
136	1.96k	dst[0] = src[0];
137	1.96k	dst[1] = src[2];
138	1.96k	dst[2] = src[1];
139	1.96k	}
140	1.33k	else
141	1.33k	{
142		/* src[2] < src[0] <= src[1] */
143	1.33k	dst[0] = src[2];
144	1.33k	dst[1] = src[0];
145	1.33k	dst[2] = src[1];
146	1.33k	}
147	70.4k	}
148	3.58k	else
149	3.58k	{
150	3.58k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.35k	{
152		/* src[1] < src[0] <= src[2] */
153	1.35k	dst[0] = src[1];
154	1.35k	dst[1] = src[0];
155	1.35k	dst[2] = src[2];
156	1.35k	}
157	2.22k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.38k	{
159		/* src[1] <= src[2] < src[0] */
160	1.38k	dst[0] = src[1];
161	1.38k	dst[1] = src[2];
162	1.38k	dst[2] = src[0];
163	1.38k	}
164	845	else
165	845	{
166		/* src[2] < src[1] < src[0] */
167	845	dst[0] = src[2];
168	845	dst[1] = src[1];
169	845	dst[2] = src[0];
170	845	}
171	3.58k	}
172	74.0k	break;
173	670k	default:
174	670k	{
175	670k	size_t n1 = n / 2;
176	670k	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	670k	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	670k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	670k	merge (tmp, n1, dst + n1, n2, dst);
184	670k	}
185	670k	break;
186	1.36M	}
187	1.36M	}
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	1.66M	case 2:
201		/* Trivial case. */
202	1.66M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.66M	{
204		/* src[0] <= src[1] */
205	1.66M	}
206	1.33k	else
207	1.33k	{
208	1.33k	ELEMENT t = src[0];
209	1.33k	src[0] = src[1];
210	1.33k	src[1] = t;
211	1.33k	}
212	1.66M	break;
213	18.4k	case 3:
214		/* Simple case. */
215	18.4k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.5k	{
217	14.5k	if (COMPARE (&src[1], &src[2]) <= 0)
218	12.0k	{
219		/* src[0] <= src[1] <= src[2] */
220	12.0k	}
221	2.50k	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	1.28k	else
229	1.28k	{
230		/* src[2] < src[0] <= src[1] */
231	1.28k	ELEMENT t = src[0];
232	1.28k	src[0] = src[2];
233	1.28k	src[2] = src[1];
234	1.28k	src[1] = t;
235	1.28k	}
236	14.5k	}
237	3.89k	else
238	3.89k	{
239	3.89k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.03k	{
241		/* src[1] < src[0] <= src[2] */
242	1.03k	ELEMENT t = src[0];
243	1.03k	src[0] = src[1];
244	1.03k	src[1] = t;
245	1.03k	}
246	2.86k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.60k	{
248		/* src[1] <= src[2] < src[0] */
249	1.60k	ELEMENT t = src[0];
250	1.60k	src[0] = src[1];
251	1.60k	src[1] = src[2];
252	1.60k	src[2] = t;
253	1.60k	}
254	1.25k	else
255	1.25k	{
256		/* src[2] < src[1] < src[0] */
257	1.25k	ELEMENT t = src[0];
258	1.25k	src[0] = src[2];
259	1.25k	src[2] = t;
260	1.25k	}
261	3.89k	}
262	18.4k	break;
263	24.1k	default:
264	24.1k	{
265	24.1k	size_t n1 = n / 2;
266	24.1k	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	24.1k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	24.1k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	24.1k	merge (tmp, n1, src + n1, n2, src);
274	24.1k	}
275	24.1k	break;
276	1.71M	}
277	1.71M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC