/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: 2025-12-31 07:08

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	70.0k	{
49	70.0k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	407k	{
51	407k	if (COMPARE (src1, src2) <= 0)
52	353k	{
53	353k	dst++ = src1++;
54	353k	n1--;
55	353k	if (n1 == 0)
56	66.6k	break;
57	353k	}
58	54.5k	else
59	54.5k	{
60	54.5k	dst++ = src2++;
61	54.5k	n2--;
62	54.5k	if (n2 == 0)
63	3.47k	break;
64	54.5k	}
65	407k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	70.0k	if (n1 > 0)
68	3.47k	{
69	3.47k	if (dst != src1)
70	3.47k	do
71	5.55k	{
72	5.55k	dst++ = src1++;
73	5.55k	n1--;
74	5.55k	}
75	5.55k	while (n1 > 0);
76	3.47k	}
77	66.6k	else /* n2 > 0 */
78	66.6k	{
79	66.6k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	66.6k	}
87	70.0k	}
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	120k	{
100	120k	switch (n)
101	120k	{
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	60.2k	case 2:
109		/* Trivial case. */
110	60.2k	if (COMPARE (&src[0], &src[1]) <= 0)
111	56.4k	{
112		/* src[0] <= src[1] */
113	56.4k	dst[0] = src[0];
114	56.4k	dst[1] = src[1];
115	56.4k	}
116	3.85k	else
117	3.85k	{
118	3.85k	dst[0] = src[1];
119	3.85k	dst[1] = src[0];
120	3.85k	}
121	60.2k	break;
122	9.80k	case 3:
123		/* Simple case. */
124	9.80k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.47k	{
126	7.47k	if (COMPARE (&src[1], &src[2]) <= 0)
127	5.26k	{
128		/* src[0] <= src[1] <= src[2] */
129	5.26k	dst[0] = src[0];
130	5.26k	dst[1] = src[1];
131	5.26k	dst[2] = src[2];
132	5.26k	}
133	2.21k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.41k	{
135		/* src[0] <= src[2] < src[1] */
136	1.41k	dst[0] = src[0];
137	1.41k	dst[1] = src[2];
138	1.41k	dst[2] = src[1];
139	1.41k	}
140	799	else
141	799	{
142		/* src[2] < src[0] <= src[1] */
143	799	dst[0] = src[2];
144	799	dst[1] = src[0];
145	799	dst[2] = src[1];
146	799	}
147	7.47k	}
148	2.33k	else
149	2.33k	{
150	2.33k	if (COMPARE (&src[0], &src[2]) <= 0)
151	922	{
152		/* src[1] < src[0] <= src[2] */
153	922	dst[0] = src[1];
154	922	dst[1] = src[0];
155	922	dst[2] = src[2];
156	922	}
157	1.41k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	770	{
159		/* src[1] <= src[2] < src[0] */
160	770	dst[0] = src[1];
161	770	dst[1] = src[2];
162	770	dst[2] = src[0];
163	770	}
164	642	else
165	642	{
166		/* src[2] < src[1] < src[0] */
167	642	dst[0] = src[2];
168	642	dst[1] = src[1];
169	642	dst[2] = src[0];
170	642	}
171	2.33k	}
172	9.80k	break;
173	50.5k	default:
174	50.5k	{
175	50.5k	size_t n1 = n / 2;
176	50.5k	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	50.5k	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	50.5k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	50.5k	merge (tmp, n1, dst + n1, n2, dst);
184	50.5k	}
185	50.5k	break;
186	120k	}
187	120k	}
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	102k	{
194	102k	switch (n)
195	102k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	85.9k	case 2:
201		/* Trivial case. */
202	85.9k	if (COMPARE (&src[0], &src[1]) <= 0)
203	85.2k	{
204		/* src[0] <= src[1] */
205	85.2k	}
206	688	else
207	688	{
208	688	ELEMENT t = src[0];
209	688	src[0] = src[1];
210	688	src[1] = t;
211	688	}
212	85.9k	break;
213	6.16k	case 3:
214		/* Simple case. */
215	6.16k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.42k	{
217	4.42k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.28k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.28k	}
221	1.13k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	601	{
223		/* src[0] <= src[2] < src[1] */
224	601	ELEMENT t = src[1];
225	601	src[1] = src[2];
226	601	src[2] = t;
227	601	}
228	535	else
229	535	{
230		/* src[2] < src[0] <= src[1] */
231	535	ELEMENT t = src[0];
232	535	src[0] = src[2];
233	535	src[2] = src[1];
234	535	src[1] = t;
235	535	}
236	4.42k	}
237	1.74k	else
238	1.74k	{
239	1.74k	if (COMPARE (&src[0], &src[2]) <= 0)
240	655	{
241		/* src[1] < src[0] <= src[2] */
242	655	ELEMENT t = src[0];
243	655	src[0] = src[1];
244	655	src[1] = t;
245	655	}
246	1.09k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	626	{
248		/* src[1] <= src[2] < src[0] */
249	626	ELEMENT t = src[0];
250	626	src[0] = src[1];
251	626	src[1] = src[2];
252	626	src[2] = t;
253	626	}
254	464	else
255	464	{
256		/* src[2] < src[1] < src[0] */
257	464	ELEMENT t = src[0];
258	464	src[0] = src[2];
259	464	src[2] = t;
260	464	}
261	1.74k	}
262	6.16k	break;
263	10.2k	default:
264	10.2k	{
265	10.2k	size_t n1 = n / 2;
266	10.2k	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	10.2k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	10.2k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	10.2k	merge (tmp, n1, src + n1, n2, src);
274	10.2k	}
275	10.2k	break;
276	102k	}
277	102k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC