/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: 2026-03-31 06:55

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	768k	{
49	768k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	11.6M	{
51	11.6M	if (COMPARE (src1, src2) <= 0)
52	10.3M	{
53	10.3M	dst++ = src1++;
54	10.3M	n1--;
55	10.3M	if (n1 == 0)
56	762k	break;
57	10.3M	}
58	1.34M	else
59	1.34M	{
60	1.34M	dst++ = src2++;
61	1.34M	n2--;
62	1.34M	if (n2 == 0)
63	6.49k	break;
64	1.34M	}
65	11.6M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	768k	if (n1 > 0)
68	6.49k	{
69	6.49k	if (dst != src1)
70	6.49k	do
71	18.4k	{
72	18.4k	dst++ = src1++;
73	18.4k	n1--;
74	18.4k	}
75	18.4k	while (n1 > 0);
76	6.49k	}
77	762k	else /* n2 > 0 */
78	762k	{
79	762k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	762k	}
87	768k	}
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	1.51M	{
100	1.51M	switch (n)
101	1.51M	{
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	2.72k	else
117	2.72k	{
118	2.72k	dst[0] = src[1];
119	2.72k	dst[1] = src[0];
120	2.72k	}
121	688k	break;
122	80.0k	case 3:
123		/* Simple case. */
124	80.0k	if (COMPARE (&src[0], &src[1]) <= 0)
125	76.5k	{
126	76.5k	if (COMPARE (&src[1], &src[2]) <= 0)
127	73.4k	{
128		/* src[0] <= src[1] <= src[2] */
129	73.4k	dst[0] = src[0];
130	73.4k	dst[1] = src[1];
131	73.4k	dst[2] = src[2];
132	73.4k	}
133	3.09k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.05k	{
135		/* src[0] <= src[2] < src[1] */
136	2.05k	dst[0] = src[0];
137	2.05k	dst[1] = src[2];
138	2.05k	dst[2] = src[1];
139	2.05k	}
140	1.03k	else
141	1.03k	{
142		/* src[2] < src[0] <= src[1] */
143	1.03k	dst[0] = src[2];
144	1.03k	dst[1] = src[0];
145	1.03k	dst[2] = src[1];
146	1.03k	}
147	76.5k	}
148	3.51k	else
149	3.51k	{
150	3.51k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.51k	{
152		/* src[1] < src[0] <= src[2] */
153	1.51k	dst[0] = src[1];
154	1.51k	dst[1] = src[0];
155	1.51k	dst[2] = src[2];
156	1.51k	}
157	2.00k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.17k	{
159		/* src[1] <= src[2] < src[0] */
160	1.17k	dst[0] = src[1];
161	1.17k	dst[1] = src[2];
162	1.17k	dst[2] = src[0];
163	1.17k	}
164	830	else
165	830	{
166		/* src[2] < src[1] < src[0] */
167	830	dst[0] = src[2];
168	830	dst[1] = src[1];
169	830	dst[2] = src[0];
170	830	}
171	3.51k	}
172	80.0k	break;
173	745k	default:
174	745k	{
175	745k	size_t n1 = n / 2;
176	745k	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	745k	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	745k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	745k	merge (tmp, n1, dst + n1, n2, dst);
184	745k	}
185	745k	break;
186	1.51M	}
187	1.51M	}
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	1.61M	{
194	1.61M	switch (n)
195	1.61M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.57M	case 2:
201		/* Trivial case. */
202	1.57M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.57M	{
204		/* src[0] <= src[1] */
205	1.57M	}
206	979	else
207	979	{
208	979	ELEMENT t = src[0];
209	979	src[0] = src[1];
210	979	src[1] = t;
211	979	}
212	1.57M	break;
213	16.9k	case 3:
214		/* Simple case. */
215	16.9k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.5k	{
217	13.5k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.1k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.1k	}
221	2.37k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.25k	{
223		/* src[0] <= src[2] < src[1] */
224	1.25k	ELEMENT t = src[1];
225	1.25k	src[1] = src[2];
226	1.25k	src[2] = t;
227	1.25k	}
228	1.11k	else
229	1.11k	{
230		/* src[2] < src[0] <= src[1] */
231	1.11k	ELEMENT t = src[0];
232	1.11k	src[0] = src[2];
233	1.11k	src[2] = src[1];
234	1.11k	src[1] = t;
235	1.11k	}
236	13.5k	}
237	3.41k	else
238	3.41k	{
239	3.41k	if (COMPARE (&src[0], &src[2]) <= 0)
240	948	{
241		/* src[1] < src[0] <= src[2] */
242	948	ELEMENT t = src[0];
243	948	src[0] = src[1];
244	948	src[1] = t;
245	948	}
246	2.46k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.37k	{
248		/* src[1] <= src[2] < src[0] */
249	1.37k	ELEMENT t = src[0];
250	1.37k	src[0] = src[1];
251	1.37k	src[1] = src[2];
252	1.37k	src[2] = t;
253	1.37k	}
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	3.41k	}
262	16.9k	break;
263	22.7k	default:
264	22.7k	{
265	22.7k	size_t n1 = n / 2;
266	22.7k	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	22.7k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	22.7k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	22.7k	merge (tmp, n1, src + n1, n2, src);
274	22.7k	}
275	22.7k	break;
276	1.61M	}
277	1.61M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC