/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: 2025-07-11 06:23

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	620k	{
49	620k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	8.92M	{
51	8.92M	if (COMPARE (src1, src2) <= 0)
52	7.92M	{
53	7.92M	dst++ = src1++;
54	7.92M	n1--;
55	7.92M	if (n1 == 0)
56	612k	break;
57	7.92M	}
58	998k	else
59	998k	{
60	998k	dst++ = src2++;
61	998k	n2--;
62	998k	if (n2 == 0)
63	7.64k	break;
64	998k	}
65	8.92M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	620k	if (n1 > 0)
68	7.64k	{
69	7.64k	if (dst != src1)
70	7.64k	do
71	18.1k	{
72	18.1k	dst++ = src1++;
73	18.1k	n1--;
74	18.1k	}
75	18.1k	while (n1 > 0);
76	7.64k	}
77	612k	else /* n2 > 0 */
78	612k	{
79	612k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	612k	}
87	620k	}
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	1.21M	{
100	1.21M	switch (n)
101	1.21M	{
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	589k	case 2:
109		/* Trivial case. */
110	589k	if (COMPARE (&src[0], &src[1]) <= 0)
111	583k	{
112		/* src[0] <= src[1] */
113	583k	dst[0] = src[0];
114	583k	dst[1] = src[1];
115	583k	}
116	6.10k	else
117	6.10k	{
118	6.10k	dst[0] = src[1];
119	6.10k	dst[1] = src[0];
120	6.10k	}
121	589k	break;
122	30.0k	case 3:
123		/* Simple case. */
124	30.0k	if (COMPARE (&src[0], &src[1]) <= 0)
125	27.0k	{
126	27.0k	if (COMPARE (&src[1], &src[2]) <= 0)
127	24.5k	{
128		/* src[0] <= src[1] <= src[2] */
129	24.5k	dst[0] = src[0];
130	24.5k	dst[1] = src[1];
131	24.5k	dst[2] = src[2];
132	24.5k	}
133	2.48k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.45k	{
135		/* src[0] <= src[2] < src[1] */
136	1.45k	dst[0] = src[0];
137	1.45k	dst[1] = src[2];
138	1.45k	dst[2] = src[1];
139	1.45k	}
140	1.03k	else
141	1.03k	{
142		/* src[2] < src[0] <= src[1] */
143	1.03k	dst[0] = src[2];
144	1.03k	dst[1] = src[0];
145	1.03k	dst[2] = src[1];
146	1.03k	}
147	27.0k	}
148	3.03k	else
149	3.03k	{
150	3.03k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.04k	{
152		/* src[1] < src[0] <= src[2] */
153	1.04k	dst[0] = src[1];
154	1.04k	dst[1] = src[0];
155	1.04k	dst[2] = src[2];
156	1.04k	}
157	1.99k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	954	{
159		/* src[1] <= src[2] < src[0] */
160	954	dst[0] = src[1];
161	954	dst[1] = src[2];
162	954	dst[2] = src[0];
163	954	}
164	1.04k	else
165	1.04k	{
166		/* src[2] < src[1] < src[0] */
167	1.04k	dst[0] = src[2];
168	1.04k	dst[1] = src[1];
169	1.04k	dst[2] = src[0];
170	1.04k	}
171	3.03k	}
172	30.0k	break;
173	596k	default:
174	596k	{
175	596k	size_t n1 = n / 2;
176	596k	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	596k	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	596k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	596k	merge (tmp, n1, dst + n1, n2, dst);
184	596k	}
185	596k	break;
186	1.21M	}
187	1.21M	}
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	1.34M	{
194	1.34M	switch (n)
195	1.34M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.30M	case 2:
201		/* Trivial case. */
202	1.30M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.30M	{
204		/* src[0] <= src[1] */
205	1.30M	}
206	1.12k	else
207	1.12k	{
208	1.12k	ELEMENT t = src[0];
209	1.12k	src[0] = src[1];
210	1.12k	src[1] = t;
211	1.12k	}
212	1.30M	break;
213	19.2k	case 3:
214		/* Simple case. */
215	19.2k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.6k	{
217	14.6k	if (COMPARE (&src[1], &src[2]) <= 0)
218	12.6k	{
219		/* src[0] <= src[1] <= src[2] */
220	12.6k	}
221	2.03k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.07k	{
223		/* src[0] <= src[2] < src[1] */
224	1.07k	ELEMENT t = src[1];
225	1.07k	src[1] = src[2];
226	1.07k	src[2] = t;
227	1.07k	}
228	965	else
229	965	{
230		/* src[2] < src[0] <= src[1] */
231	965	ELEMENT t = src[0];
232	965	src[0] = src[2];
233	965	src[2] = src[1];
234	965	src[1] = t;
235	965	}
236	14.6k	}
237	4.59k	else
238	4.59k	{
239	4.59k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.03k	{
241		/* src[1] < src[0] <= src[2] */
242	1.03k	ELEMENT t = src[0];
243	1.03k	src[0] = src[1];
244	1.03k	src[1] = t;
245	1.03k	}
246	3.56k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	2.13k	{
248		/* src[1] <= src[2] < src[0] */
249	2.13k	ELEMENT t = src[0];
250	2.13k	src[0] = src[1];
251	2.13k	src[1] = src[2];
252	2.13k	src[2] = t;
253	2.13k	}
254	1.43k	else
255	1.43k	{
256		/* src[2] < src[1] < src[0] */
257	1.43k	ELEMENT t = src[0];
258	1.43k	src[0] = src[2];
259	1.43k	src[2] = t;
260	1.43k	}
261	4.59k	}
262	19.2k	break;
263	23.0k	default:
264	23.0k	{
265	23.0k	size_t n1 = n / 2;
266	23.0k	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	23.0k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	23.0k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	23.0k	merge (tmp, n1, src + n1, n2, src);
274	23.0k	}
275	23.0k	break;
276	1.34M	}
277	1.34M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC