/src/libidn2/gl/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: 2026-09-03 07:15

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	45.6k	{
49	45.6k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	316k	{
51	316k	if (COMPARE (src1, src2) <= 0)
52	250k	{
53	250k	dst++ = src1++;
54	250k	n1--;
55	250k	if (n1 == 0)
56	42.6k	break;
57	250k	}
58	65.7k	else
59	65.7k	{
60	65.7k	dst++ = src2++;
61	65.7k	n2--;
62	65.7k	if (n2 == 0)
63	2.98k	break;
64	65.7k	}
65	316k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	45.6k	if (n1 > 0)
68	2.98k	{
69	2.98k	if (dst != src1)
70	2.98k	do
71	6.00k	{
72	6.00k	dst++ = src1++;
73	6.00k	n1--;
74	6.00k	}
75	6.00k	while (n1 > 0);
76	2.98k	}
77	42.6k	else /* n2 > 0 */
78	42.6k	{
79	42.6k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	42.6k	}
87	45.6k	}
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	79.2k	{
100	79.2k	switch (n)
101	79.2k	{
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	36.2k	case 2:
109		/* Trivial case. */
110	36.2k	if (COMPARE (&src[0], &src[1]) <= 0)
111	33.0k	{
112		/* src[0] <= src[1] */
113	33.0k	dst[0] = src[0];
114	33.0k	dst[1] = src[1];
115	33.0k	}
116	3.17k	else
117	3.17k	{
118	3.17k	dst[0] = src[1];
119	3.17k	dst[1] = src[0];
120	3.17k	}
121	36.2k	break;
122	9.38k	case 3:
123		/* Simple case. */
124	9.38k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.22k	{
126	7.22k	if (COMPARE (&src[1], &src[2]) <= 0)
127	4.85k	{
128		/* src[0] <= src[1] <= src[2] */
129	4.85k	dst[0] = src[0];
130	4.85k	dst[1] = src[1];
131	4.85k	dst[2] = src[2];
132	4.85k	}
133	2.36k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.02k	{
135		/* src[0] <= src[2] < src[1] */
136	2.02k	dst[0] = src[0];
137	2.02k	dst[1] = src[2];
138	2.02k	dst[2] = src[1];
139	2.02k	}
140	345	else
141	345	{
142		/* src[2] < src[0] <= src[1] */
143	345	dst[0] = src[2];
144	345	dst[1] = src[0];
145	345	dst[2] = src[1];
146	345	}
147	7.22k	}
148	2.15k	else
149	2.15k	{
150	2.15k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.42k	{
152		/* src[1] < src[0] <= src[2] */
153	1.42k	dst[0] = src[1];
154	1.42k	dst[1] = src[0];
155	1.42k	dst[2] = src[2];
156	1.42k	}
157	737	else if (COMPARE (&src[1], &src[2]) <= 0)
158	460	{
159		/* src[1] <= src[2] < src[0] */
160	460	dst[0] = src[1];
161	460	dst[1] = src[2];
162	460	dst[2] = src[0];
163	460	}
164	277	else
165	277	{
166		/* src[2] < src[1] < src[0] */
167	277	dst[0] = src[2];
168	277	dst[1] = src[1];
169	277	dst[2] = src[0];
170	277	}
171	2.15k	}
172	9.38k	break;
173	33.6k	default:
174	33.6k	{
175	33.6k	size_t n1 = n / 2;
176	33.6k	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	33.6k	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	33.6k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	33.6k	merge (tmp, n1, dst + n1, n2, dst);
184	33.6k	}
185	33.6k	break;
186	79.2k	}
187	79.2k	}
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	35.5k	{
194	35.5k	switch (n)
195	35.5k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	15.9k	case 2:
201		/* Trivial case. */
202	15.9k	if (COMPARE (&src[0], &src[1]) <= 0)
203	15.2k	{
204		/* src[0] <= src[1] */
205	15.2k	}
206	627	else
207	627	{
208	627	ELEMENT t = src[0];
209	627	src[0] = src[1];
210	627	src[1] = t;
211	627	}
212	15.9k	break;
213	7.71k	case 3:
214		/* Simple case. */
215	7.71k	if (COMPARE (&src[0], &src[1]) <= 0)
216	6.27k	{
217	6.27k	if (COMPARE (&src[1], &src[2]) <= 0)
218	5.36k	{
219		/* src[0] <= src[1] <= src[2] */
220	5.36k	}
221	908	else if (COMPARE (&src[0], &src[2]) <= 0)
222	527	{
223		/* src[0] <= src[2] < src[1] */
224	527	ELEMENT t = src[1];
225	527	src[1] = src[2];
226	527	src[2] = t;
227	527	}
228	381	else
229	381	{
230		/* src[2] < src[0] <= src[1] */
231	381	ELEMENT t = src[0];
232	381	src[0] = src[2];
233	381	src[2] = src[1];
234	381	src[1] = t;
235	381	}
236	6.27k	}
237	1.43k	else
238	1.43k	{
239	1.43k	if (COMPARE (&src[0], &src[2]) <= 0)
240	657	{
241		/* src[1] < src[0] <= src[2] */
242	657	ELEMENT t = src[0];
243	657	src[0] = src[1];
244	657	src[1] = t;
245	657	}
246	781	else if (COMPARE (&src[1], &src[2]) <= 0)
247	412	{
248		/* src[1] <= src[2] < src[0] */
249	412	ELEMENT t = src[0];
250	412	src[0] = src[1];
251	412	src[1] = src[2];
252	412	src[2] = t;
253	412	}
254	369	else
255	369	{
256		/* src[2] < src[1] < src[0] */
257	369	ELEMENT t = src[0];
258	369	src[0] = src[2];
259	369	src[2] = t;
260	369	}
261	1.43k	}
262	7.71k	break;
263	11.9k	default:
264	11.9k	{
265	11.9k	size_t n1 = n / 2;
266	11.9k	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	11.9k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	11.9k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	11.9k	merge (tmp, n1, src + n1, n2, src);
274	11.9k	}
275	11.9k	break;
276	35.5k	}
277	35.5k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC