/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: 2025-09-04 07:15

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	681k	{
49	681k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.77M	{
51	9.77M	if (COMPARE (src1, src2) <= 0)
52	8.85M	{
53	8.85M	dst++ = src1++;
54	8.85M	n1--;
55	8.85M	if (n1 == 0)
56	676k	break;
57	8.85M	}
58	919k	else
59	919k	{
60	919k	dst++ = src2++;
61	919k	n2--;
62	919k	if (n2 == 0)
63	5.53k	break;
64	919k	}
65	9.77M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	681k	if (n1 > 0)
68	5.53k	{
69	5.53k	if (dst != src1)
70	5.53k	do
71	17.6k	{
72	17.6k	dst++ = src1++;
73	17.6k	n1--;
74	17.6k	}
75	17.6k	while (n1 > 0);
76	5.53k	}
77	676k	else /* n2 > 0 */
78	676k	{
79	676k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	676k	}
87	681k	}
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	1.33M	{
100	1.33M	switch (n)
101	1.33M	{
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	639k	case 2:
109		/* Trivial case. */
110	639k	if (COMPARE (&src[0], &src[1]) <= 0)
111	637k	{
112		/* src[0] <= src[1] */
113	637k	dst[0] = src[0];
114	637k	dst[1] = src[1];
115	637k	}
116	2.63k	else
117	2.63k	{
118	2.63k	dst[0] = src[1];
119	2.63k	dst[1] = src[0];
120	2.63k	}
121	639k	break;
122	42.0k	case 3:
123		/* Simple case. */
124	42.0k	if (COMPARE (&src[0], &src[1]) <= 0)
125	38.7k	{
126	38.7k	if (COMPARE (&src[1], &src[2]) <= 0)
127	35.8k	{
128		/* src[0] <= src[1] <= src[2] */
129	35.8k	dst[0] = src[0];
130	35.8k	dst[1] = src[1];
131	35.8k	dst[2] = src[2];
132	35.8k	}
133	2.97k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.86k	{
135		/* src[0] <= src[2] < src[1] */
136	1.86k	dst[0] = src[0];
137	1.86k	dst[1] = src[2];
138	1.86k	dst[2] = src[1];
139	1.86k	}
140	1.10k	else
141	1.10k	{
142		/* src[2] < src[0] <= src[1] */
143	1.10k	dst[0] = src[2];
144	1.10k	dst[1] = src[0];
145	1.10k	dst[2] = src[1];
146	1.10k	}
147	38.7k	}
148	3.25k	else
149	3.25k	{
150	3.25k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.38k	{
152		/* src[1] < src[0] <= src[2] */
153	1.38k	dst[0] = src[1];
154	1.38k	dst[1] = src[0];
155	1.38k	dst[2] = src[2];
156	1.38k	}
157	1.86k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	863	{
159		/* src[1] <= src[2] < src[0] */
160	863	dst[0] = src[1];
161	863	dst[1] = src[2];
162	863	dst[2] = src[0];
163	863	}
164	1.00k	else
165	1.00k	{
166		/* src[2] < src[1] < src[0] */
167	1.00k	dst[0] = src[2];
168	1.00k	dst[1] = src[1];
169	1.00k	dst[2] = src[0];
170	1.00k	}
171	3.25k	}
172	42.0k	break;
173	657k	default:
174	657k	{
175	657k	size_t n1 = n / 2;
176	657k	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	657k	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	657k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	657k	merge (tmp, n1, dst + n1, n2, dst);
184	657k	}
185	657k	break;
186	1.33M	}
187	1.33M	}
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	1.43M	{
194	1.43M	switch (n)
195	1.43M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.39M	case 2:
201		/* Trivial case. */
202	1.39M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.39M	{
204		/* src[0] <= src[1] */
205	1.39M	}
206	1.06k	else
207	1.06k	{
208	1.06k	ELEMENT t = src[0];
209	1.06k	src[0] = src[1];
210	1.06k	src[1] = t;
211	1.06k	}
212	1.39M	break;
213	18.4k	case 3:
214		/* Simple case. */
215	18.4k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.2k	{
217	14.2k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.6k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.6k	}
221	2.65k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.42k	{
223		/* src[0] <= src[2] < src[1] */
224	1.42k	ELEMENT t = src[1];
225	1.42k	src[1] = src[2];
226	1.42k	src[2] = t;
227	1.42k	}
228	1.22k	else
229	1.22k	{
230		/* src[2] < src[0] <= src[1] */
231	1.22k	ELEMENT t = src[0];
232	1.22k	src[0] = src[2];
233	1.22k	src[2] = src[1];
234	1.22k	src[1] = t;
235	1.22k	}
236	14.2k	}
237	4.21k	else
238	4.21k	{
239	4.21k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.02k	{
241		/* src[1] < src[0] <= src[2] */
242	1.02k	ELEMENT t = src[0];
243	1.02k	src[0] = src[1];
244	1.02k	src[1] = t;
245	1.02k	}
246	3.19k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.81k	{
248		/* src[1] <= src[2] < src[0] */
249	1.81k	ELEMENT t = src[0];
250	1.81k	src[0] = src[1];
251	1.81k	src[1] = src[2];
252	1.81k	src[2] = t;
253	1.81k	}
254	1.37k	else
255	1.37k	{
256		/* src[2] < src[1] < src[0] */
257	1.37k	ELEMENT t = src[0];
258	1.37k	src[0] = src[2];
259	1.37k	src[2] = t;
260	1.37k	}
261	4.21k	}
262	18.4k	break;
263	24.4k	default:
264	24.4k	{
265	24.4k	size_t n1 = n / 2;
266	24.4k	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	24.4k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	24.4k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	24.4k	merge (tmp, n1, src + n1, n2, src);
274	24.4k	}
275	24.4k	break;
276	1.43M	}
277	1.43M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC