/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: 2025-08-28 06:41

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	606k	{
49	606k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	8.74M	{
51	8.74M	if (COMPARE (src1, src2) <= 0)
52	7.84M	{
53	7.84M	dst++ = src1++;
54	7.84M	n1--;
55	7.84M	if (n1 == 0)
56	600k	break;
57	7.84M	}
58	904k	else
59	904k	{
60	904k	dst++ = src2++;
61	904k	n2--;
62	904k	if (n2 == 0)
63	6.53k	break;
64	904k	}
65	8.74M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	606k	if (n1 > 0)
68	6.53k	{
69	6.53k	if (dst != src1)
70	6.53k	do
71	17.5k	{
72	17.5k	dst++ = src1++;
73	17.5k	n1--;
74	17.5k	}
75	17.5k	while (n1 > 0);
76	6.53k	}
77	600k	else /* n2 > 0 */
78	600k	{
79	600k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	600k	}
87	606k	}
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	1.18M	{
100	1.18M	switch (n)
101	1.18M	{
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	578k	case 2:
109		/* Trivial case. */
110	578k	if (COMPARE (&src[0], &src[1]) <= 0)
111	575k	{
112		/* src[0] <= src[1] */
113	575k	dst[0] = src[0];
114	575k	dst[1] = src[1];
115	575k	}
116	2.87k	else
117	2.87k	{
118	2.87k	dst[0] = src[1];
119	2.87k	dst[1] = src[0];
120	2.87k	}
121	578k	break;
122	28.1k	case 3:
123		/* Simple case. */
124	28.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	20.9k	{
126	20.9k	if (COMPARE (&src[1], &src[2]) <= 0)
127	17.4k	{
128		/* src[0] <= src[1] <= src[2] */
129	17.4k	dst[0] = src[0];
130	17.4k	dst[1] = src[1];
131	17.4k	dst[2] = src[2];
132	17.4k	}
133	3.52k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	2.11k	{
135		/* src[0] <= src[2] < src[1] */
136	2.11k	dst[0] = src[0];
137	2.11k	dst[1] = src[2];
138	2.11k	dst[2] = src[1];
139	2.11k	}
140	1.40k	else
141	1.40k	{
142		/* src[2] < src[0] <= src[1] */
143	1.40k	dst[0] = src[2];
144	1.40k	dst[1] = src[0];
145	1.40k	dst[2] = src[1];
146	1.40k	}
147	20.9k	}
148	7.20k	else
149	7.20k	{
150	7.20k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.46k	{
152		/* src[1] < src[0] <= src[2] */
153	1.46k	dst[0] = src[1];
154	1.46k	dst[1] = src[0];
155	1.46k	dst[2] = src[2];
156	1.46k	}
157	5.73k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.59k	{
159		/* src[1] <= src[2] < src[0] */
160	1.59k	dst[0] = src[1];
161	1.59k	dst[1] = src[2];
162	1.59k	dst[2] = src[0];
163	1.59k	}
164	4.14k	else
165	4.14k	{
166		/* src[2] < src[1] < src[0] */
167	4.14k	dst[0] = src[2];
168	4.14k	dst[1] = src[1];
169	4.14k	dst[2] = src[0];
170	4.14k	}
171	7.20k	}
172	28.1k	break;
173	582k	default:
174	582k	{
175	582k	size_t n1 = n / 2;
176	582k	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	582k	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	582k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	582k	merge (tmp, n1, dst + n1, n2, dst);
184	582k	}
185	582k	break;
186	1.18M	}
187	1.18M	}
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	1.40M	{
194	1.40M	switch (n)
195	1.40M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.36M	case 2:
201		/* Trivial case. */
202	1.36M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.35M	{
204		/* src[0] <= src[1] */
205	1.35M	}
206	1.40k	else
207	1.40k	{
208	1.40k	ELEMENT t = src[0];
209	1.40k	src[0] = src[1];
210	1.40k	src[1] = t;
211	1.40k	}
212	1.36M	break;
213	18.8k	case 3:
214		/* Simple case. */
215	18.8k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.2k	{
217	14.2k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.1k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.1k	}
221	3.09k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.30k	{
223		/* src[0] <= src[2] < src[1] */
224	1.30k	ELEMENT t = src[1];
225	1.30k	src[1] = src[2];
226	1.30k	src[2] = t;
227	1.30k	}
228	1.79k	else
229	1.79k	{
230		/* src[2] < src[0] <= src[1] */
231	1.79k	ELEMENT t = src[0];
232	1.79k	src[0] = src[2];
233	1.79k	src[2] = src[1];
234	1.79k	src[1] = t;
235	1.79k	}
236	14.2k	}
237	4.61k	else
238	4.61k	{
239	4.61k	if (COMPARE (&src[0], &src[2]) <= 0)
240	978	{
241		/* src[1] < src[0] <= src[2] */
242	978	ELEMENT t = src[0];
243	978	src[0] = src[1];
244	978	src[1] = t;
245	978	}
246	3.63k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	2.08k	{
248		/* src[1] <= src[2] < src[0] */
249	2.08k	ELEMENT t = src[0];
250	2.08k	src[0] = src[1];
251	2.08k	src[1] = src[2];
252	2.08k	src[2] = t;
253	2.08k	}
254	1.55k	else
255	1.55k	{
256		/* src[2] < src[1] < src[0] */
257	1.55k	ELEMENT t = src[0];
258	1.55k	src[0] = src[2];
259	1.55k	src[2] = t;
260	1.55k	}
261	4.61k	}
262	18.8k	break;
263	23.8k	default:
264	23.8k	{
265	23.8k	size_t n1 = n / 2;
266	23.8k	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	23.8k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	23.8k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	23.8k	merge (tmp, n1, src + n1, n2, src);
274	23.8k	}
275	23.8k	break;
276	1.40M	}
277	1.40M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC