/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: 2026-10-13 06:37

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	733k	{
49	733k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.5M	{
51	10.5M	if (COMPARE (src1, src2) <= 0)
52	9.45M	{
53	9.45M	dst++ = src1++;
54	9.45M	n1--;
55	9.45M	if (n1 == 0)
56	726k	break;
57	9.45M	}
58	1.13M	else
59	1.13M	{
60	1.13M	dst++ = src2++;
61	1.13M	n2--;
62	1.13M	if (n2 == 0)
63	7.01k	break;
64	1.13M	}
65	10.5M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	733k	if (n1 > 0)
68	7.01k	{
69	7.01k	if (dst != src1)
70	7.01k	do
71	19.3k	{
72	19.3k	dst++ = src1++;
73	19.3k	n1--;
74	19.3k	}
75	19.3k	while (n1 > 0);
76	7.01k	}
77	726k	else /* n2 > 0 */
78	726k	{
79	726k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	726k	}
87	733k	}
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	1.43M	{
100	1.43M	switch (n)
101	1.43M	{
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	654k	case 2:
109		/* Trivial case. */
110	654k	if (COMPARE (&src[0], &src[1]) <= 0)
111	650k	{
112		/* src[0] <= src[1] */
113	650k	dst[0] = src[0];
114	650k	dst[1] = src[1];
115	650k	}
116	3.69k	else
117	3.69k	{
118	3.69k	dst[0] = src[1];
119	3.69k	dst[1] = src[0];
120	3.69k	}
121	654k	break;
122	78.8k	case 3:
123		/* Simple case. */
124	78.8k	if (COMPARE (&src[0], &src[1]) <= 0)
125	74.4k	{
126	74.4k	if (COMPARE (&src[1], &src[2]) <= 0)
127	70.7k	{
128		/* src[0] <= src[1] <= src[2] */
129	70.7k	dst[0] = src[0];
130	70.7k	dst[1] = src[1];
131	70.7k	dst[2] = src[2];
132	70.7k	}
133	3.69k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.08k	{
135		/* src[0] <= src[2] < src[1] */
136	2.08k	dst[0] = src[0];
137	2.08k	dst[1] = src[2];
138	2.08k	dst[2] = src[1];
139	2.08k	}
140	1.61k	else
141	1.61k	{
142		/* src[2] < src[0] <= src[1] */
143	1.61k	dst[0] = src[2];
144	1.61k	dst[1] = src[0];
145	1.61k	dst[2] = src[1];
146	1.61k	}
147	74.4k	}
148	4.38k	else
149	4.38k	{
150	4.38k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.55k	{
152		/* src[1] < src[0] <= src[2] */
153	1.55k	dst[0] = src[1];
154	1.55k	dst[1] = src[0];
155	1.55k	dst[2] = src[2];
156	1.55k	}
157	2.83k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.88k	{
159		/* src[1] <= src[2] < src[0] */
160	1.88k	dst[0] = src[1];
161	1.88k	dst[1] = src[2];
162	1.88k	dst[2] = src[0];
163	1.88k	}
164	945	else
165	945	{
166		/* src[2] < src[1] < src[0] */
167	945	dst[0] = src[2];
168	945	dst[1] = src[1];
169	945	dst[2] = src[0];
170	945	}
171	4.38k	}
172	78.8k	break;
173	706k	default:
174	706k	{
175	706k	size_t n1 = n / 2;
176	706k	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	706k	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	706k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	706k	merge (tmp, n1, dst + n1, n2, dst);
184	706k	}
185	706k	break;
186	1.43M	}
187	1.43M	}
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	1.78M	{
194	1.78M	switch (n)
195	1.78M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.73M	case 2:
201		/* Trivial case. */
202	1.73M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.73M	{
204		/* src[0] <= src[1] */
205	1.73M	}
206	1.42k	else
207	1.42k	{
208	1.42k	ELEMENT t = src[0];
209	1.42k	src[0] = src[1];
210	1.42k	src[1] = t;
211	1.42k	}
212	1.73M	break;
213	19.4k	case 3:
214		/* Simple case. */
215	19.4k	if (COMPARE (&src[0], &src[1]) <= 0)
216	15.4k	{
217	15.4k	if (COMPARE (&src[1], &src[2]) <= 0)
218	12.7k	{
219		/* src[0] <= src[1] <= src[2] */
220	12.7k	}
221	2.64k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.26k	{
223		/* src[0] <= src[2] < src[1] */
224	1.26k	ELEMENT t = src[1];
225	1.26k	src[1] = src[2];
226	1.26k	src[2] = t;
227	1.26k	}
228	1.37k	else
229	1.37k	{
230		/* src[2] < src[0] <= src[1] */
231	1.37k	ELEMENT t = src[0];
232	1.37k	src[0] = src[2];
233	1.37k	src[2] = src[1];
234	1.37k	src[1] = t;
235	1.37k	}
236	15.4k	}
237	4.04k	else
238	4.04k	{
239	4.04k	if (COMPARE (&src[0], &src[2]) <= 0)
240	997	{
241		/* src[1] < src[0] <= src[2] */
242	997	ELEMENT t = src[0];
243	997	src[0] = src[1];
244	997	src[1] = t;
245	997	}
246	3.05k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.69k	{
248		/* src[1] <= src[2] < src[0] */
249	1.69k	ELEMENT t = src[0];
250	1.69k	src[0] = src[1];
251	1.69k	src[1] = src[2];
252	1.69k	src[2] = t;
253	1.69k	}
254	1.35k	else
255	1.35k	{
256		/* src[2] < src[1] < src[0] */
257	1.35k	ELEMENT t = src[0];
258	1.35k	src[0] = src[2];
259	1.35k	src[2] = t;
260	1.35k	}
261	4.04k	}
262	19.4k	break;
263	27.1k	default:
264	27.1k	{
265	27.1k	size_t n1 = n / 2;
266	27.1k	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	27.1k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	27.1k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	27.1k	merge (tmp, n1, src + n1, n2, src);
274	27.1k	}
275	27.1k	break;
276	1.78M	}
277	1.78M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC