/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: 2025-11-16 06:28

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	75.6k	{
49	75.6k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	447k	{
51	447k	if (COMPARE (src1, src2) <= 0)
52	393k	{
53	393k	dst++ = src1++;
54	393k	n1--;
55	393k	if (n1 == 0)
56	72.1k	break;
57	393k	}
58	53.8k	else
59	53.8k	{
60	53.8k	dst++ = src2++;
61	53.8k	n2--;
62	53.8k	if (n2 == 0)
63	3.52k	break;
64	53.8k	}
65	447k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	75.6k	if (n1 > 0)
68	3.52k	{
69	3.52k	if (dst != src1)
70	3.52k	do
71	5.69k	{
72	5.69k	dst++ = src1++;
73	5.69k	n1--;
74	5.69k	}
75	5.69k	while (n1 > 0);
76	3.52k	}
77	72.1k	else /* n2 > 0 */
78	72.1k	{
79	72.1k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	72.1k	}
87	75.6k	}
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	131k	{
100	131k	switch (n)
101	131k	{
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	65.4k	case 2:
109		/* Trivial case. */
110	65.4k	if (COMPARE (&src[0], &src[1]) <= 0)
111	61.7k	{
112		/* src[0] <= src[1] */
113	61.7k	dst[0] = src[0];
114	61.7k	dst[1] = src[1];
115	61.7k	}
116	3.67k	else
117	3.67k	{
118	3.67k	dst[0] = src[1];
119	3.67k	dst[1] = src[0];
120	3.67k	}
121	65.4k	break;
122	10.2k	case 3:
123		/* Simple case. */
124	10.2k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.95k	{
126	7.95k	if (COMPARE (&src[1], &src[2]) <= 0)
127	5.80k	{
128		/* src[0] <= src[1] <= src[2] */
129	5.80k	dst[0] = src[0];
130	5.80k	dst[1] = src[1];
131	5.80k	dst[2] = src[2];
132	5.80k	}
133	2.14k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.30k	{
135		/* src[0] <= src[2] < src[1] */
136	1.30k	dst[0] = src[0];
137	1.30k	dst[1] = src[2];
138	1.30k	dst[2] = src[1];
139	1.30k	}
140	839	else
141	839	{
142		/* src[2] < src[0] <= src[1] */
143	839	dst[0] = src[2];
144	839	dst[1] = src[0];
145	839	dst[2] = src[1];
146	839	}
147	7.95k	}
148	2.33k	else
149	2.33k	{
150	2.33k	if (COMPARE (&src[0], &src[2]) <= 0)
151	939	{
152		/* src[1] < src[0] <= src[2] */
153	939	dst[0] = src[1];
154	939	dst[1] = src[0];
155	939	dst[2] = src[2];
156	939	}
157	1.39k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	740	{
159		/* src[1] <= src[2] < src[0] */
160	740	dst[0] = src[1];
161	740	dst[1] = src[2];
162	740	dst[2] = src[0];
163	740	}
164	651	else
165	651	{
166		/* src[2] < src[1] < src[0] */
167	651	dst[0] = src[2];
168	651	dst[1] = src[1];
169	651	dst[2] = src[0];
170	651	}
171	2.33k	}
172	10.2k	break;
173	55.8k	default:
174	55.8k	{
175	55.8k	size_t n1 = n / 2;
176	55.8k	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	55.8k	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	55.8k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	55.8k	merge (tmp, n1, dst + n1, n2, dst);
184	55.8k	}
185	55.8k	break;
186	131k	}
187	131k	}
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	100k	{
194	100k	switch (n)
195	100k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	82.1k	case 2:
201		/* Trivial case. */
202	82.1k	if (COMPARE (&src[0], &src[1]) <= 0)
203	81.5k	{
204		/* src[0] <= src[1] */
205	81.5k	}
206	655	else
207	655	{
208	655	ELEMENT t = src[0];
209	655	src[0] = src[1];
210	655	src[1] = t;
211	655	}
212	82.1k	break;
213	8.22k	case 3:
214		/* Simple case. */
215	8.22k	if (COMPARE (&src[0], &src[1]) <= 0)
216	6.46k	{
217	6.46k	if (COMPARE (&src[1], &src[2]) <= 0)
218	5.29k	{
219		/* src[0] <= src[1] <= src[2] */
220	5.29k	}
221	1.16k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	627	{
223		/* src[0] <= src[2] < src[1] */
224	627	ELEMENT t = src[1];
225	627	src[1] = src[2];
226	627	src[2] = t;
227	627	}
228	538	else
229	538	{
230		/* src[2] < src[0] <= src[1] */
231	538	ELEMENT t = src[0];
232	538	src[0] = src[2];
233	538	src[2] = src[1];
234	538	src[1] = t;
235	538	}
236	6.46k	}
237	1.76k	else
238	1.76k	{
239	1.76k	if (COMPARE (&src[0], &src[2]) <= 0)
240	688	{
241		/* src[1] < src[0] <= src[2] */
242	688	ELEMENT t = src[0];
243	688	src[0] = src[1];
244	688	src[1] = t;
245	688	}
246	1.07k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	631	{
248		/* src[1] <= src[2] < src[0] */
249	631	ELEMENT t = src[0];
250	631	src[0] = src[1];
251	631	src[1] = src[2];
252	631	src[2] = t;
253	631	}
254	446	else
255	446	{
256		/* src[2] < src[1] < src[0] */
257	446	ELEMENT t = src[0];
258	446	src[0] = src[2];
259	446	src[2] = t;
260	446	}
261	1.76k	}
262	8.22k	break;
263	9.89k	default:
264	9.89k	{
265	9.89k	size_t n1 = n / 2;
266	9.89k	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	9.89k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	9.89k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	9.89k	merge (tmp, n1, src + n1, n2, src);
274	9.89k	}
275	9.89k	break;
276	100k	}
277	100k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC