/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: 2025-12-12 07:21

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	698k	{
49	698k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.4M	{
51	10.4M	if (COMPARE (src1, src2) <= 0)
52	9.21M	{
53	9.21M	dst++ = src1++;
54	9.21M	n1--;
55	9.21M	if (n1 == 0)
56	691k	break;
57	9.21M	}
58	1.20M	else
59	1.20M	{
60	1.20M	dst++ = src2++;
61	1.20M	n2--;
62	1.20M	if (n2 == 0)
63	6.88k	break;
64	1.20M	}
65	10.4M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	698k	if (n1 > 0)
68	6.88k	{
69	6.88k	if (dst != src1)
70	6.88k	do
71	14.9k	{
72	14.9k	dst++ = src1++;
73	14.9k	n1--;
74	14.9k	}
75	14.9k	while (n1 > 0);
76	6.88k	}
77	691k	else /* n2 > 0 */
78	691k	{
79	691k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	691k	}
87	698k	}
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	1.37M	{
100	1.37M	switch (n)
101	1.37M	{
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	634k	case 2:
109		/* Trivial case. */
110	634k	if (COMPARE (&src[0], &src[1]) <= 0)
111	630k	{
112		/* src[0] <= src[1] */
113	630k	dst[0] = src[0];
114	630k	dst[1] = src[1];
115	630k	}
116	3.77k	else
117	3.77k	{
118	3.77k	dst[0] = src[1];
119	3.77k	dst[1] = src[0];
120	3.77k	}
121	634k	break;
122	64.2k	case 3:
123		/* Simple case. */
124	64.2k	if (COMPARE (&src[0], &src[1]) <= 0)
125	59.9k	{
126	59.9k	if (COMPARE (&src[1], &src[2]) <= 0)
127	56.6k	{
128		/* src[0] <= src[1] <= src[2] */
129	56.6k	dst[0] = src[0];
130	56.6k	dst[1] = src[1];
131	56.6k	dst[2] = src[2];
132	56.6k	}
133	3.34k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.07k	{
135		/* src[0] <= src[2] < src[1] */
136	2.07k	dst[0] = src[0];
137	2.07k	dst[1] = src[2];
138	2.07k	dst[2] = src[1];
139	2.07k	}
140	1.27k	else
141	1.27k	{
142		/* src[2] < src[0] <= src[1] */
143	1.27k	dst[0] = src[2];
144	1.27k	dst[1] = src[0];
145	1.27k	dst[2] = src[1];
146	1.27k	}
147	59.9k	}
148	4.23k	else
149	4.23k	{
150	4.23k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.89k	{
152		/* src[1] < src[0] <= src[2] */
153	1.89k	dst[0] = src[1];
154	1.89k	dst[1] = src[0];
155	1.89k	dst[2] = src[2];
156	1.89k	}
157	2.33k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.56k	{
159		/* src[1] <= src[2] < src[0] */
160	1.56k	dst[0] = src[1];
161	1.56k	dst[1] = src[2];
162	1.56k	dst[2] = src[0];
163	1.56k	}
164	772	else
165	772	{
166		/* src[2] < src[1] < src[0] */
167	772	dst[0] = src[2];
168	772	dst[1] = src[1];
169	772	dst[2] = src[0];
170	772	}
171	4.23k	}
172	64.2k	break;
173	674k	default:
174	674k	{
175	674k	size_t n1 = n / 2;
176	674k	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	674k	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	674k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	674k	merge (tmp, n1, dst + n1, n2, dst);
184	674k	}
185	674k	break;
186	1.37M	}
187	1.37M	}
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	1.66M	{
194	1.66M	switch (n)
195	1.66M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.62M	case 2:
201		/* Trivial case. */
202	1.62M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.62M	{
204		/* src[0] <= src[1] */
205	1.62M	}
206	1.06k	else
207	1.06k	{
208	1.06k	ELEMENT t = src[0];
209	1.06k	src[0] = src[1];
210	1.06k	src[1] = t;
211	1.06k	}
212	1.62M	break;
213	17.3k	case 3:
214		/* Simple case. */
215	17.3k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.5k	{
217	13.5k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.9k	}
221	2.59k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.29k	{
223		/* src[0] <= src[2] < src[1] */
224	1.29k	ELEMENT t = src[1];
225	1.29k	src[1] = src[2];
226	1.29k	src[2] = t;
227	1.29k	}
228	1.30k	else
229	1.30k	{
230		/* src[2] < src[0] <= src[1] */
231	1.30k	ELEMENT t = src[0];
232	1.30k	src[0] = src[2];
233	1.30k	src[2] = src[1];
234	1.30k	src[1] = t;
235	1.30k	}
236	13.5k	}
237	3.78k	else
238	3.78k	{
239	3.78k	if (COMPARE (&src[0], &src[2]) <= 0)
240	952	{
241		/* src[1] < src[0] <= src[2] */
242	952	ELEMENT t = src[0];
243	952	src[0] = src[1];
244	952	src[1] = t;
245	952	}
246	2.82k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.76k	{
248		/* src[1] <= src[2] < src[0] */
249	1.76k	ELEMENT t = src[0];
250	1.76k	src[0] = src[1];
251	1.76k	src[1] = src[2];
252	1.76k	src[2] = t;
253	1.76k	}
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	3.78k	}
262	17.3k	break;
263	24.5k	default:
264	24.5k	{
265	24.5k	size_t n1 = n / 2;
266	24.5k	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	24.5k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	24.5k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	24.5k	merge (tmp, n1, src + n1, n2, src);
274	24.5k	}
275	24.5k	break;
276	1.66M	}
277	1.66M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC