/src/libunistring/lib/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: 2025-07-17 06:59

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	658k	{
49	658k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.41M	{
51	9.41M	if (COMPARE (src1, src2) <= 0)
52	8.47M	{
53	8.47M	dst++ = src1++;
54	8.47M	n1--;
55	8.47M	if (n1 == 0)
56	654k	break;
57	8.47M	}
58	947k	else
59	947k	{
60	947k	dst++ = src2++;
61	947k	n2--;
62	947k	if (n2 == 0)
63	4.67k	break;
64	947k	}
65	9.41M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	658k	if (n1 > 0)
68	4.67k	{
69	4.67k	if (dst != src1)
70	4.67k	do
71	15.3k	{
72	15.3k	dst++ = src1++;
73	15.3k	n1--;
74	15.3k	}
75	15.3k	while (n1 > 0);
76	4.67k	}
77	654k	else /* n2 > 0 */
78	654k	{
79	654k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	654k	}
87	658k	}
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	1.29M	{
100	1.29M	switch (n)
101	1.29M	{
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	632k	case 2:
109		/* Trivial case. */
110	632k	if (COMPARE (&src[0], &src[1]) <= 0)
111	630k	{
112		/* src[0] <= src[1] */
113	630k	dst[0] = src[0];
114	630k	dst[1] = src[1];
115	630k	}
116	2.16k	else
117	2.16k	{
118	2.16k	dst[0] = src[1];
119	2.16k	dst[1] = src[0];
120	2.16k	}
121	632k	break;
122	26.1k	case 3:
123		/* Simple case. */
124	26.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	23.4k	{
126	23.4k	if (COMPARE (&src[1], &src[2]) <= 0)
127	21.2k	{
128		/* src[0] <= src[1] <= src[2] */
129	21.2k	dst[0] = src[0];
130	21.2k	dst[1] = src[1];
131	21.2k	dst[2] = src[2];
132	21.2k	}
133	2.24k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.29k	{
135		/* src[0] <= src[2] < src[1] */
136	1.29k	dst[0] = src[0];
137	1.29k	dst[1] = src[2];
138	1.29k	dst[2] = src[1];
139	1.29k	}
140	947	else
141	947	{
142		/* src[2] < src[0] <= src[1] */
143	947	dst[0] = src[2];
144	947	dst[1] = src[0];
145	947	dst[2] = src[1];
146	947	}
147	23.4k	}
148	2.69k	else
149	2.69k	{
150	2.69k	if (COMPARE (&src[0], &src[2]) <= 0)
151	930	{
152		/* src[1] < src[0] <= src[2] */
153	930	dst[0] = src[1];
154	930	dst[1] = src[0];
155	930	dst[2] = src[2];
156	930	}
157	1.76k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	879	{
159		/* src[1] <= src[2] < src[0] */
160	879	dst[0] = src[1];
161	879	dst[1] = src[2];
162	879	dst[2] = src[0];
163	879	}
164	884	else
165	884	{
166		/* src[2] < src[1] < src[0] */
167	884	dst[0] = src[2];
168	884	dst[1] = src[1];
169	884	dst[2] = src[0];
170	884	}
171	2.69k	}
172	26.1k	break;
173	636k	default:
174	636k	{
175	636k	size_t n1 = n / 2;
176	636k	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	636k	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	636k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	636k	merge (tmp, n1, dst + n1, n2, dst);
184	636k	}
185	636k	break;
186	1.29M	}
187	1.29M	}
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	1.42M	{
194	1.42M	switch (n)
195	1.42M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.38M	case 2:
201		/* Trivial case. */
202	1.38M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.38M	{
204		/* src[0] <= src[1] */
205	1.38M	}
206	993	else
207	993	{
208	993	ELEMENT t = src[0];
209	993	src[0] = src[1];
210	993	src[1] = t;
211	993	}
212	1.38M	break;
213	18.2k	case 3:
214		/* Simple case. */
215	18.2k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.0k	{
217	14.0k	if (COMPARE (&src[1], &src[2]) <= 0)
218	12.1k	{
219		/* src[0] <= src[1] <= src[2] */
220	12.1k	}
221	1.92k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	996	{
223		/* src[0] <= src[2] < src[1] */
224	996	ELEMENT t = src[1];
225	996	src[1] = src[2];
226	996	src[2] = t;
227	996	}
228	930	else
229	930	{
230		/* src[2] < src[0] <= src[1] */
231	930	ELEMENT t = src[0];
232	930	src[0] = src[2];
233	930	src[2] = src[1];
234	930	src[1] = t;
235	930	}
236	14.0k	}
237	4.19k	else
238	4.19k	{
239	4.19k	if (COMPARE (&src[0], &src[2]) <= 0)
240	966	{
241		/* src[1] < src[0] <= src[2] */
242	966	ELEMENT t = src[0];
243	966	src[0] = src[1];
244	966	src[1] = t;
245	966	}
246	3.22k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.87k	{
248		/* src[1] <= src[2] < src[0] */
249	1.87k	ELEMENT t = src[0];
250	1.87k	src[0] = src[1];
251	1.87k	src[1] = src[2];
252	1.87k	src[2] = t;
253	1.87k	}
254	1.34k	else
255	1.34k	{
256		/* src[2] < src[1] < src[0] */
257	1.34k	ELEMENT t = src[0];
258	1.34k	src[0] = src[2];
259	1.34k	src[2] = t;
260	1.34k	}
261	4.19k	}
262	18.2k	break;
263	21.7k	default:
264	21.7k	{
265	21.7k	size_t n1 = n / 2;
266	21.7k	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	21.7k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	21.7k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	21.7k	merge (tmp, n1, src + n1, n2, src);
274	21.7k	}
275	21.7k	break;
276	1.42M	}
277	1.42M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC