/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: 2026-07-12 06:46

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	642k	{
49	642k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.79M	{
51	9.79M	if (COMPARE (src1, src2) <= 0)
52	8.76M	{
53	8.76M	dst++ = src1++;
54	8.76M	n1--;
55	8.76M	if (n1 == 0)
56	636k	break;
57	8.76M	}
58	1.03M	else
59	1.03M	{
60	1.03M	dst++ = src2++;
61	1.03M	n2--;
62	1.03M	if (n2 == 0)
63	5.56k	break;
64	1.03M	}
65	9.79M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	642k	if (n1 > 0)
68	5.56k	{
69	5.56k	if (dst != src1)
70	5.56k	do
71	15.8k	{
72	15.8k	dst++ = src1++;
73	15.8k	n1--;
74	15.8k	}
75	15.8k	while (n1 > 0);
76	5.56k	}
77	636k	else /* n2 > 0 */
78	636k	{
79	636k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	636k	}
87	642k	}
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	1.27M	{
100	1.27M	switch (n)
101	1.27M	{
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	586k	case 2:
109		/* Trivial case. */
110	586k	if (COMPARE (&src[0], &src[1]) <= 0)
111	583k	{
112		/* src[0] <= src[1] */
113	583k	dst[0] = src[0];
114	583k	dst[1] = src[1];
115	583k	}
116	2.92k	else
117	2.92k	{
118	2.92k	dst[0] = src[1];
119	2.92k	dst[1] = src[0];
120	2.92k	}
121	586k	break;
122	56.1k	case 3:
123		/* Simple case. */
124	56.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	52.5k	{
126	52.5k	if (COMPARE (&src[1], &src[2]) <= 0)
127	49.1k	{
128		/* src[0] <= src[1] <= src[2] */
129	49.1k	dst[0] = src[0];
130	49.1k	dst[1] = src[1];
131	49.1k	dst[2] = src[2];
132	49.1k	}
133	3.41k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.15k	{
135		/* src[0] <= src[2] < src[1] */
136	2.15k	dst[0] = src[0];
137	2.15k	dst[1] = src[2];
138	2.15k	dst[2] = src[1];
139	2.15k	}
140	1.26k	else
141	1.26k	{
142		/* src[2] < src[0] <= src[1] */
143	1.26k	dst[0] = src[2];
144	1.26k	dst[1] = src[0];
145	1.26k	dst[2] = src[1];
146	1.26k	}
147	52.5k	}
148	3.58k	else
149	3.58k	{
150	3.58k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.80k	{
152		/* src[1] < src[0] <= src[2] */
153	1.80k	dst[0] = src[1];
154	1.80k	dst[1] = src[0];
155	1.80k	dst[2] = src[2];
156	1.80k	}
157	1.78k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.18k	{
159		/* src[1] <= src[2] < src[0] */
160	1.18k	dst[0] = src[1];
161	1.18k	dst[1] = src[2];
162	1.18k	dst[2] = src[0];
163	1.18k	}
164	594	else
165	594	{
166		/* src[2] < src[1] < src[0] */
167	594	dst[0] = src[2];
168	594	dst[1] = src[1];
169	594	dst[2] = src[0];
170	594	}
171	3.58k	}
172	56.1k	break;
173	628k	default:
174	628k	{
175	628k	size_t n1 = n / 2;
176	628k	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	628k	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	628k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	628k	merge (tmp, n1, dst + n1, n2, dst);
184	628k	}
185	628k	break;
186	1.27M	}
187	1.27M	}
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	1.65M	{
194	1.65M	switch (n)
195	1.65M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.63M	case 2:
201		/* Trivial case. */
202	1.63M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.63M	{
204		/* src[0] <= src[1] */
205	1.63M	}
206	1.63k	else
207	1.63k	{
208	1.63k	ELEMENT t = src[0];
209	1.63k	src[0] = src[1];
210	1.63k	src[1] = t;
211	1.63k	}
212	1.63M	break;
213	6.75k	case 3:
214		/* Simple case. */
215	6.75k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.61k	{
217	4.61k	if (COMPARE (&src[1], &src[2]) <= 0)
218	2.61k	{
219		/* src[0] <= src[1] <= src[2] */
220	2.61k	}
221	1.99k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.14k	{
223		/* src[0] <= src[2] < src[1] */
224	1.14k	ELEMENT t = src[1];
225	1.14k	src[1] = src[2];
226	1.14k	src[2] = t;
227	1.14k	}
228	851	else
229	851	{
230		/* src[2] < src[0] <= src[1] */
231	851	ELEMENT t = src[0];
232	851	src[0] = src[2];
233	851	src[2] = src[1];
234	851	src[1] = t;
235	851	}
236	4.61k	}
237	2.14k	else
238	2.14k	{
239	2.14k	if (COMPARE (&src[0], &src[2]) <= 0)
240	676	{
241		/* src[1] < src[0] <= src[2] */
242	676	ELEMENT t = src[0];
243	676	src[0] = src[1];
244	676	src[1] = t;
245	676	}
246	1.46k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	861	{
248		/* src[1] <= src[2] < src[0] */
249	861	ELEMENT t = src[0];
250	861	src[0] = src[1];
251	861	src[1] = src[2];
252	861	src[2] = t;
253	861	}
254	607	else
255	607	{
256		/* src[2] < src[1] < src[0] */
257	607	ELEMENT t = src[0];
258	607	src[0] = src[2];
259	607	src[2] = t;
260	607	}
261	2.14k	}
262	6.75k	break;
263	13.6k	default:
264	13.6k	{
265	13.6k	size_t n1 = n / 2;
266	13.6k	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	13.6k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	13.6k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	13.6k	merge (tmp, n1, src + n1, n2, src);
274	13.6k	}
275	13.6k	break;
276	1.65M	}
277	1.65M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC