/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 06:37

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	17.7k	{
49	17.7k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	93.3k	{
51	93.3k	if (COMPARE (src1, src2) <= 0)
52	81.7k	{
53	81.7k	dst++ = src1++;
54	81.7k	n1--;
55	81.7k	if (n1 == 0)
56	16.6k	break;
57	81.7k	}
58	11.6k	else
59	11.6k	{
60	11.6k	dst++ = src2++;
61	11.6k	n2--;
62	11.6k	if (n2 == 0)
63	1.11k	break;
64	11.6k	}
65	93.3k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	17.7k	if (n1 > 0)
68	1.11k	{
69	1.11k	if (dst != src1)
70	1.11k	do
71	1.87k	{
72	1.87k	dst++ = src1++;
73	1.87k	n1--;
74	1.87k	}
75	1.87k	while (n1 > 0);
76	1.11k	}
77	16.6k	else /* n2 > 0 */
78	16.6k	{
79	16.6k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	16.6k	}
87	17.7k	}
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	28.3k	{
100	28.3k	switch (n)
101	28.3k	{
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	14.4k	case 2:
109		/* Trivial case. */
110	14.4k	if (COMPARE (&src[0], &src[1]) <= 0)
111	13.8k	{
112		/* src[0] <= src[1] */
113	13.8k	dst[0] = src[0];
114	13.8k	dst[1] = src[1];
115	13.8k	}
116	635	else
117	635	{
118	635	dst[0] = src[1];
119	635	dst[1] = src[0];
120	635	}
121	14.4k	break;
122	3.26k	case 3:
123		/* Simple case. */
124	3.26k	if (COMPARE (&src[0], &src[1]) <= 0)
125	2.74k	{
126	2.74k	if (COMPARE (&src[1], &src[2]) <= 0)
127	2.26k	{
128		/* src[0] <= src[1] <= src[2] */
129	2.26k	dst[0] = src[0];
130	2.26k	dst[1] = src[1];
131	2.26k	dst[2] = src[2];
132	2.26k	}
133	477	else if (COMPARE (&src[0], &src[2]) <= 0)
134	262	{
135		/* src[0] <= src[2] < src[1] */
136	262	dst[0] = src[0];
137	262	dst[1] = src[2];
138	262	dst[2] = src[1];
139	262	}
140	215	else
141	215	{
142		/* src[2] < src[0] <= src[1] */
143	215	dst[0] = src[2];
144	215	dst[1] = src[0];
145	215	dst[2] = src[1];
146	215	}
147	2.74k	}
148	519	else
149	519	{
150	519	if (COMPARE (&src[0], &src[2]) <= 0)
151	233	{
152		/* src[1] < src[0] <= src[2] */
153	233	dst[0] = src[1];
154	233	dst[1] = src[0];
155	233	dst[2] = src[2];
156	233	}
157	286	else if (COMPARE (&src[1], &src[2]) <= 0)
158	206	{
159		/* src[1] <= src[2] < src[0] */
160	206	dst[0] = src[1];
161	206	dst[1] = src[2];
162	206	dst[2] = src[0];
163	206	}
164	80	else
165	80	{
166		/* src[2] < src[1] < src[0] */
167	80	dst[0] = src[2];
168	80	dst[1] = src[1];
169	80	dst[2] = src[0];
170	80	}
171	519	}
172	3.26k	break;
173	10.5k	default:
174	10.5k	{
175	10.5k	size_t n1 = n / 2;
176	10.5k	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	10.5k	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	10.5k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	10.5k	merge (tmp, n1, dst + n1, n2, dst);
184	10.5k	}
185	10.5k	break;
186	28.3k	}
187	28.3k	}
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	18.5k	{
194	18.5k	switch (n)
195	18.5k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	6.45k	case 2:
201		/* Trivial case. */
202	6.45k	if (COMPARE (&src[0], &src[1]) <= 0)
203	6.18k	{
204		/* src[0] <= src[1] */
205	6.18k	}
206	269	else
207	269	{
208	269	ELEMENT t = src[0];
209	269	src[0] = src[1];
210	269	src[1] = t;
211	269	}
212	6.45k	break;
213	4.92k	case 3:
214		/* Simple case. */
215	4.92k	if (COMPARE (&src[0], &src[1]) <= 0)
216	3.51k	{
217	3.51k	if (COMPARE (&src[1], &src[2]) <= 0)
218	2.97k	{
219		/* src[0] <= src[1] <= src[2] */
220	2.97k	}
221	541	else if (COMPARE (&src[0], &src[2]) <= 0)
222	241	{
223		/* src[0] <= src[2] < src[1] */
224	241	ELEMENT t = src[1];
225	241	src[1] = src[2];
226	241	src[2] = t;
227	241	}
228	300	else
229	300	{
230		/* src[2] < src[0] <= src[1] */
231	300	ELEMENT t = src[0];
232	300	src[0] = src[2];
233	300	src[2] = src[1];
234	300	src[1] = t;
235	300	}
236	3.51k	}
237	1.41k	else
238	1.41k	{
239	1.41k	if (COMPARE (&src[0], &src[2]) <= 0)
240	519	{
241		/* src[1] < src[0] <= src[2] */
242	519	ELEMENT t = src[0];
243	519	src[0] = src[1];
244	519	src[1] = t;
245	519	}
246	892	else if (COMPARE (&src[1], &src[2]) <= 0)
247	686	{
248		/* src[1] <= src[2] < src[0] */
249	686	ELEMENT t = src[0];
250	686	src[0] = src[1];
251	686	src[1] = src[2];
252	686	src[2] = t;
253	686	}
254	206	else
255	206	{
256		/* src[2] < src[1] < src[0] */
257	206	ELEMENT t = src[0];
258	206	src[0] = src[2];
259	206	src[2] = t;
260	206	}
261	1.41k	}
262	4.92k	break;
263	7.16k	default:
264	7.16k	{
265	7.16k	size_t n1 = n / 2;
266	7.16k	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	7.16k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	7.16k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	7.16k	merge (tmp, n1, src + n1, n2, src);
274	7.16k	}
275	7.16k	break;
276	18.5k	}
277	18.5k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC