/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: 2025-11-09 06:32

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	694k	{
49	694k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.2M	{
51	10.2M	if (COMPARE (src1, src2) <= 0)
52	9.27M	{
53	9.27M	dst++ = src1++;
54	9.27M	n1--;
55	9.27M	if (n1 == 0)
56	689k	break;
57	9.27M	}
58	945k	else
59	945k	{
60	945k	dst++ = src2++;
61	945k	n2--;
62	945k	if (n2 == 0)
63	4.80k	break;
64	945k	}
65	10.2M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	694k	if (n1 > 0)
68	4.80k	{
69	4.80k	if (dst != src1)
70	4.80k	do
71	15.9k	{
72	15.9k	dst++ = src1++;
73	15.9k	n1--;
74	15.9k	}
75	15.9k	while (n1 > 0);
76	4.80k	}
77	689k	else /* n2 > 0 */
78	689k	{
79	689k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	689k	}
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	628k	case 2:
109		/* Trivial case. */
110	628k	if (COMPARE (&src[0], &src[1]) <= 0)
111	626k	{
112		/* src[0] <= src[1] */
113	626k	dst[0] = src[0];
114	626k	dst[1] = src[1];
115	626k	}
116	1.96k	else
117	1.96k	{
118	1.96k	dst[0] = src[1];
119	1.96k	dst[1] = src[0];
120	1.96k	}
121	628k	break;
122	65.4k	case 3:
123		/* Simple case. */
124	65.4k	if (COMPARE (&src[0], &src[1]) <= 0)
125	62.5k	{
126	62.5k	if (COMPARE (&src[1], &src[2]) <= 0)
127	60.0k	{
128		/* src[0] <= src[1] <= src[2] */
129	60.0k	dst[0] = src[0];
130	60.0k	dst[1] = src[1];
131	60.0k	dst[2] = src[2];
132	60.0k	}
133	2.49k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.62k	{
135		/* src[0] <= src[2] < src[1] */
136	1.62k	dst[0] = src[0];
137	1.62k	dst[1] = src[2];
138	1.62k	dst[2] = src[1];
139	1.62k	}
140	869	else
141	869	{
142		/* src[2] < src[0] <= src[1] */
143	869	dst[0] = src[2];
144	869	dst[1] = src[0];
145	869	dst[2] = src[1];
146	869	}
147	62.5k	}
148	2.87k	else
149	2.87k	{
150	2.87k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.24k	{
152		/* src[1] < src[0] <= src[2] */
153	1.24k	dst[0] = src[1];
154	1.24k	dst[1] = src[0];
155	1.24k	dst[2] = src[2];
156	1.24k	}
157	1.63k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	825	{
159		/* src[1] <= src[2] < src[0] */
160	825	dst[0] = src[1];
161	825	dst[1] = src[2];
162	825	dst[2] = src[0];
163	825	}
164	811	else
165	811	{
166		/* src[2] < src[1] < src[0] */
167	811	dst[0] = src[2];
168	811	dst[1] = src[1];
169	811	dst[2] = src[0];
170	811	}
171	2.87k	}
172	65.4k	break;
173	671k	default:
174	671k	{
175	671k	size_t n1 = n / 2;
176	671k	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	671k	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	671k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	671k	merge (tmp, n1, dst + n1, n2, dst);
184	671k	}
185	671k	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	1.51M	{
194	1.51M	switch (n)
195	1.51M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.47M	case 2:
201		/* Trivial case. */
202	1.47M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.47M	{
204		/* src[0] <= src[1] */
205	1.47M	}
206	1.00k	else
207	1.00k	{
208	1.00k	ELEMENT t = src[0];
209	1.00k	src[0] = src[1];
210	1.00k	src[1] = t;
211	1.00k	}
212	1.47M	break;
213	17.0k	case 3:
214		/* Simple case. */
215	17.0k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.2k	{
217	13.2k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.8k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.8k	}
221	2.41k	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	1.06k	else
229	1.06k	{
230		/* src[2] < src[0] <= src[1] */
231	1.06k	ELEMENT t = src[0];
232	1.06k	src[0] = src[2];
233	1.06k	src[2] = src[1];
234	1.06k	src[1] = t;
235	1.06k	}
236	13.2k	}
237	3.78k	else
238	3.78k	{
239	3.78k	if (COMPARE (&src[0], &src[2]) <= 0)
240	959	{
241		/* src[1] < src[0] <= src[2] */
242	959	ELEMENT t = src[0];
243	959	src[0] = src[1];
244	959	src[1] = t;
245	959	}
246	2.82k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.63k	{
248		/* src[1] <= src[2] < src[0] */
249	1.63k	ELEMENT t = src[0];
250	1.63k	src[0] = src[1];
251	1.63k	src[1] = src[2];
252	1.63k	src[2] = t;
253	1.63k	}
254	1.18k	else
255	1.18k	{
256		/* src[2] < src[1] < src[0] */
257	1.18k	ELEMENT t = src[0];
258	1.18k	src[0] = src[2];
259	1.18k	src[2] = t;
260	1.18k	}
261	3.78k	}
262	17.0k	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	1.51M	}
277	1.51M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC