/src/libidn2/unistring/array-mergesort.h

Source (jump to first uncovered line)
/* 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: 2025-07-12 06:18

Line	Count	Source (jump to first uncovered line)
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	44.2k	{
49	44.2k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	312k	{
51	312k	if (COMPARE (src1, src2) <= 0)
52	246k	{
53	246k	dst++ = src1++;
54	246k	n1--;
55	246k	if (n1 == 0)
56	41.2k	break;
57	246k	}
58	65.7k	else
59	65.7k	{
60	65.7k	dst++ = src2++;
61	65.7k	n2--;
62	65.7k	if (n2 == 0)
63	3.02k	break;
64	65.7k	}
65	312k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	44.2k	if (n1 > 0)
68	3.02k	{
69	3.02k	if (dst != src1)
70	3.02k	do
71	6.26k	{
72	6.26k	dst++ = src1++;
73	6.26k	n1--;
74	6.26k	}
75	6.26k	while (n1 > 0);
76	3.02k	}
77	41.2k	else /* n2 > 0 */
78	41.2k	{
79	41.2k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	41.2k	}
87	44.2k	}
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	77.2k	{
100	77.2k	switch (n)
101	77.2k	{
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	34.8k	case 2:
109		/* Trivial case. */
110	34.8k	if (COMPARE (&src[0], &src[1]) <= 0)
111	31.4k	{
112		/* src[0] <= src[1] */
113	31.4k	dst[0] = src[0];
114	31.4k	dst[1] = src[1];
115	31.4k	}
116	3.37k	else
117	3.37k	{
118	3.37k	dst[0] = src[1];
119	3.37k	dst[1] = src[0];
120	3.37k	}
121	34.8k	break;
122	9.43k	case 3:
123		/* Simple case. */
124	9.43k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.45k	{
126	7.45k	if (COMPARE (&src[1], &src[2]) <= 0)
127	5.37k	{
128		/* src[0] <= src[1] <= src[2] */
129	5.37k	dst[0] = src[0];
130	5.37k	dst[1] = src[1];
131	5.37k	dst[2] = src[2];
132	5.37k	}
133	2.08k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.71k	{
135		/* src[0] <= src[2] < src[1] */
136	1.71k	dst[0] = src[0];
137	1.71k	dst[1] = src[2];
138	1.71k	dst[2] = src[1];
139	1.71k	}
140	367	else
141	367	{
142		/* src[2] < src[0] <= src[1] */
143	367	dst[0] = src[2];
144	367	dst[1] = src[0];
145	367	dst[2] = src[1];
146	367	}
147	7.45k	}
148	1.98k	else
149	1.98k	{
150	1.98k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.24k	{
152		/* src[1] < src[0] <= src[2] */
153	1.24k	dst[0] = src[1];
154	1.24k	dst[1] = src[0];
155	1.24k	dst[2] = src[2];
156	1.24k	}
157	742	else if (COMPARE (&src[1], &src[2]) <= 0)
158	431	{
159		/* src[1] <= src[2] < src[0] */
160	431	dst[0] = src[1];
161	431	dst[1] = src[2];
162	431	dst[2] = src[0];
163	431	}
164	311	else
165	311	{
166		/* src[2] < src[1] < src[0] */
167	311	dst[0] = src[2];
168	311	dst[1] = src[1];
169	311	dst[2] = src[0];
170	311	}
171	1.98k	}
172	9.43k	break;
173	32.9k	default:
174	32.9k	{
175	32.9k	size_t n1 = n / 2;
176	32.9k	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	32.9k	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	32.9k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	32.9k	merge (tmp, n1, dst + n1, n2, dst);
184	32.9k	}
185	32.9k	break;
186	77.2k	}
187	77.2k	}
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	35.6k	{
194	35.6k	switch (n)
195	35.6k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	16.1k	case 2:
201		/* Trivial case. */
202	16.1k	if (COMPARE (&src[0], &src[1]) <= 0)
203	15.4k	{
204		/* src[0] <= src[1] */
205	15.4k	}
206	708	else
207	708	{
208	708	ELEMENT t = src[0];
209	708	src[0] = src[1];
210	708	src[1] = t;
211	708	}
212	16.1k	break;
213	8.14k	case 3:
214		/* Simple case. */
215	8.14k	if (COMPARE (&src[0], &src[1]) <= 0)
216	6.89k	{
217	6.89k	if (COMPARE (&src[1], &src[2]) <= 0)
218	6.06k	{
219		/* src[0] <= src[1] <= src[2] */
220	6.06k	}
221	828	else if (COMPARE (&src[0], &src[2]) <= 0)
222	474	{
223		/* src[0] <= src[2] < src[1] */
224	474	ELEMENT t = src[1];
225	474	src[1] = src[2];
226	474	src[2] = t;
227	474	}
228	354	else
229	354	{
230		/* src[2] < src[0] <= src[1] */
231	354	ELEMENT t = src[0];
232	354	src[0] = src[2];
233	354	src[2] = src[1];
234	354	src[1] = t;
235	354	}
236	6.89k	}
237	1.25k	else
238	1.25k	{
239	1.25k	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	734	else if (COMPARE (&src[1], &src[2]) <= 0)
247	435	{
248		/* src[1] <= src[2] < src[0] */
249	435	ELEMENT t = src[0];
250	435	src[0] = src[1];
251	435	src[1] = src[2];
252	435	src[2] = t;
253	435	}
254	299	else
255	299	{
256		/* src[2] < src[1] < src[0] */
257	299	ELEMENT t = src[0];
258	299	src[0] = src[2];
259	299	src[2] = t;
260	299	}
261	1.25k	}
262	8.14k	break;
263	11.3k	default:
264	11.3k	{
265	11.3k	size_t n1 = n / 2;
266	11.3k	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	11.3k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	11.3k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	11.3k	merge (tmp, n1, src + n1, n2, src);
274	11.3k	}
275	11.3k	break;
276	35.6k	}
277	35.6k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC