/src/libunistring/lib/array-mergesort.h

Source (jump to first uncovered line)
/* Stable-sorting of an array using mergesort.
   Copyright (C) 2009-2024 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: 2025-07-23 06:43

Line	Count	Source (jump to first uncovered line)
1		/* Stable-sorting of an array using mergesort.
2		Copyright (C) 2009-2024 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	16.1k	{
49	16.1k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	84.0k	{
51	84.0k	if (COMPARE (src1, src2) <= 0)
52	71.6k	{
53	71.6k	dst++ = src1++;
54	71.6k	n1--;
55	71.6k	if (n1 == 0)
56	14.9k	break;
57	71.6k	}
58	12.3k	else
59	12.3k	{
60	12.3k	dst++ = src2++;
61	12.3k	n2--;
62	12.3k	if (n2 == 0)
63	1.24k	break;
64	12.3k	}
65	84.0k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	16.1k	if (n1 > 0)
68	1.24k	{
69	1.24k	if (dst != src1)
70	1.24k	do
71	2.04k	{
72	2.04k	dst++ = src1++;
73	2.04k	n1--;
74	2.04k	}
75	2.04k	while (n1 > 0);
76	1.24k	}
77	14.9k	else /* n2 > 0 */
78	14.9k	{
79	14.9k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	14.9k	}
87	16.1k	}
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	25.3k	{
100	25.3k	switch (n)
101	25.3k	{
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	12.9k	case 2:
109		/* Trivial case. */
110	12.9k	if (COMPARE (&src[0], &src[1]) <= 0)
111	12.5k	{
112		/* src[0] <= src[1] */
113	12.5k	dst[0] = src[0];
114	12.5k	dst[1] = src[1];
115	12.5k	}
116	431	else
117	431	{
118	431	dst[0] = src[1];
119	431	dst[1] = src[0];
120	431	}
121	12.9k	break;
122	3.16k	case 3:
123		/* Simple case. */
124	3.16k	if (COMPARE (&src[0], &src[1]) <= 0)
125	2.51k	{
126	2.51k	if (COMPARE (&src[1], &src[2]) <= 0)
127	2.15k	{
128		/* src[0] <= src[1] <= src[2] */
129	2.15k	dst[0] = src[0];
130	2.15k	dst[1] = src[1];
131	2.15k	dst[2] = src[2];
132	2.15k	}
133	358	else if (COMPARE (&src[0], &src[2]) <= 0)
134	260	{
135		/* src[0] <= src[2] < src[1] */
136	260	dst[0] = src[0];
137	260	dst[1] = src[2];
138	260	dst[2] = src[1];
139	260	}
140	98	else
141	98	{
142		/* src[2] < src[0] <= src[1] */
143	98	dst[0] = src[2];
144	98	dst[1] = src[0];
145	98	dst[2] = src[1];
146	98	}
147	2.51k	}
148	651	else
149	651	{
150	651	if (COMPARE (&src[0], &src[2]) <= 0)
151	264	{
152		/* src[1] < src[0] <= src[2] */
153	264	dst[0] = src[1];
154	264	dst[1] = src[0];
155	264	dst[2] = src[2];
156	264	}
157	387	else if (COMPARE (&src[1], &src[2]) <= 0)
158	311	{
159		/* src[1] <= src[2] < src[0] */
160	311	dst[0] = src[1];
161	311	dst[1] = src[2];
162	311	dst[2] = src[0];
163	311	}
164	76	else
165	76	{
166		/* src[2] < src[1] < src[0] */
167	76	dst[0] = src[2];
168	76	dst[1] = src[1];
169	76	dst[2] = src[0];
170	76	}
171	651	}
172	3.16k	break;
173	9.20k	default:
174	9.20k	{
175	9.20k	size_t n1 = n / 2;
176	9.20k	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	9.20k	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	9.20k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	9.20k	merge (tmp, n1, dst + n1, n2, dst);
184	9.20k	}
185	9.20k	break;
186	25.3k	}
187	25.3k	}
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	21.8k	{
194	21.8k	switch (n)
195	21.8k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	8.95k	case 2:
201		/* Trivial case. */
202	8.95k	if (COMPARE (&src[0], &src[1]) <= 0)
203	8.63k	{
204		/* src[0] <= src[1] */
205	8.63k	}
206	313	else
207	313	{
208	313	ELEMENT t = src[0];
209	313	src[0] = src[1];
210	313	src[1] = t;
211	313	}
212	8.95k	break;
213	5.92k	case 3:
214		/* Simple case. */
215	5.92k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.50k	{
217	4.50k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.90k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.90k	}
221	604	else if (COMPARE (&src[0], &src[2]) <= 0)
222	286	{
223		/* src[0] <= src[2] < src[1] */
224	286	ELEMENT t = src[1];
225	286	src[1] = src[2];
226	286	src[2] = t;
227	286	}
228	318	else
229	318	{
230		/* src[2] < src[0] <= src[1] */
231	318	ELEMENT t = src[0];
232	318	src[0] = src[2];
233	318	src[2] = src[1];
234	318	src[1] = t;
235	318	}
236	4.50k	}
237	1.42k	else
238	1.42k	{
239	1.42k	if (COMPARE (&src[0], &src[2]) <= 0)
240	454	{
241		/* src[1] < src[0] <= src[2] */
242	454	ELEMENT t = src[0];
243	454	src[0] = src[1];
244	454	src[1] = t;
245	454	}
246	968	else if (COMPARE (&src[1], &src[2]) <= 0)
247	753	{
248		/* src[1] <= src[2] < src[0] */
249	753	ELEMENT t = src[0];
250	753	src[0] = src[1];
251	753	src[1] = src[2];
252	753	src[2] = t;
253	753	}
254	215	else
255	215	{
256		/* src[2] < src[1] < src[0] */
257	215	ELEMENT t = src[0];
258	215	src[0] = src[2];
259	215	src[2] = t;
260	215	}
261	1.42k	}
262	5.92k	break;
263	6.96k	default:
264	6.96k	{
265	6.96k	size_t n1 = n / 2;
266	6.96k	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	6.96k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	6.96k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	6.96k	merge (tmp, n1, src + n1, n2, src);
274	6.96k	}
275	6.96k	break;
276	21.8k	}
277	21.8k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC