/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: 2025-08-23 06:26

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	619k	{
49	619k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	8.82M	{
51	8.82M	if (COMPARE (src1, src2) <= 0)
52	7.92M	{
53	7.92M	dst++ = src1++;
54	7.92M	n1--;
55	7.92M	if (n1 == 0)
56	613k	break;
57	7.92M	}
58	903k	else
59	903k	{
60	903k	dst++ = src2++;
61	903k	n2--;
62	903k	if (n2 == 0)
63	5.27k	break;
64	903k	}
65	8.82M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	619k	if (n1 > 0)
68	5.27k	{
69	5.27k	if (dst != src1)
70	5.27k	do
71	16.8k	{
72	16.8k	dst++ = src1++;
73	16.8k	n1--;
74	16.8k	}
75	16.8k	while (n1 > 0);
76	5.27k	}
77	613k	else /* n2 > 0 */
78	613k	{
79	613k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	613k	}
87	619k	}
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	596k	case 2:
109		/* Trivial case. */
110	596k	if (COMPARE (&src[0], &src[1]) <= 0)
111	594k	{
112		/* src[0] <= src[1] */
113	594k	dst[0] = src[0];
114	594k	dst[1] = src[1];
115	594k	}
116	2.58k	else
117	2.58k	{
118	2.58k	dst[0] = src[1];
119	2.58k	dst[1] = src[0];
120	2.58k	}
121	596k	break;
122	22.3k	case 3:
123		/* Simple case. */
124	22.3k	if (COMPARE (&src[0], &src[1]) <= 0)
125	19.1k	{
126	19.1k	if (COMPARE (&src[1], &src[2]) <= 0)
127	16.7k	{
128		/* src[0] <= src[1] <= src[2] */
129	16.7k	dst[0] = src[0];
130	16.7k	dst[1] = src[1];
131	16.7k	dst[2] = src[2];
132	16.7k	}
133	2.37k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.44k	{
135		/* src[0] <= src[2] < src[1] */
136	1.44k	dst[0] = src[0];
137	1.44k	dst[1] = src[2];
138	1.44k	dst[2] = src[1];
139	1.44k	}
140	930	else
141	930	{
142		/* src[2] < src[0] <= src[1] */
143	930	dst[0] = src[2];
144	930	dst[1] = src[0];
145	930	dst[2] = src[1];
146	930	}
147	19.1k	}
148	3.14k	else
149	3.14k	{
150	3.14k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.03k	{
152		/* src[1] < src[0] <= src[2] */
153	1.03k	dst[0] = src[1];
154	1.03k	dst[1] = src[0];
155	1.03k	dst[2] = src[2];
156	1.03k	}
157	2.11k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.13k	{
159		/* src[1] <= src[2] < src[0] */
160	1.13k	dst[0] = src[1];
161	1.13k	dst[1] = src[2];
162	1.13k	dst[2] = src[0];
163	1.13k	}
164	981	else
165	981	{
166		/* src[2] < src[1] < src[0] */
167	981	dst[0] = src[2];
168	981	dst[1] = src[1];
169	981	dst[2] = src[0];
170	981	}
171	3.14k	}
172	22.3k	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	1.38M	{
194	1.38M	switch (n)
195	1.38M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.34M	case 2:
201		/* Trivial case. */
202	1.34M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.34M	{
204		/* src[0] <= src[1] */
205	1.34M	}
206	965	else
207	965	{
208	965	ELEMENT t = src[0];
209	965	src[0] = src[1];
210	965	src[1] = t;
211	965	}
212	1.34M	break;
213	17.7k	case 3:
214		/* Simple case. */
215	17.7k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.4k	{
217	13.4k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.2k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.2k	}
221	2.17k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.15k	{
223		/* src[0] <= src[2] < src[1] */
224	1.15k	ELEMENT t = src[1];
225	1.15k	src[1] = src[2];
226	1.15k	src[2] = t;
227	1.15k	}
228	1.01k	else
229	1.01k	{
230		/* src[2] < src[0] <= src[1] */
231	1.01k	ELEMENT t = src[0];
232	1.01k	src[0] = src[2];
233	1.01k	src[2] = src[1];
234	1.01k	src[1] = t;
235	1.01k	}
236	13.4k	}
237	4.30k	else
238	4.30k	{
239	4.30k	if (COMPARE (&src[0], &src[2]) <= 0)
240	780	{
241		/* src[1] < src[0] <= src[2] */
242	780	ELEMENT t = src[0];
243	780	src[0] = src[1];
244	780	src[1] = t;
245	780	}
246	3.52k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	2.04k	{
248		/* src[1] <= src[2] < src[0] */
249	2.04k	ELEMENT t = src[0];
250	2.04k	src[0] = src[1];
251	2.04k	src[1] = src[2];
252	2.04k	src[2] = t;
253	2.04k	}
254	1.47k	else
255	1.47k	{
256		/* src[2] < src[1] < src[0] */
257	1.47k	ELEMENT t = src[0];
258	1.47k	src[0] = src[2];
259	1.47k	src[2] = t;
260	1.47k	}
261	4.30k	}
262	17.7k	break;
263	22.7k	default:
264	22.7k	{
265	22.7k	size_t n1 = n / 2;
266	22.7k	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	22.7k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	22.7k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	22.7k	merge (tmp, n1, src + n1, n2, src);
274	22.7k	}
275	22.7k	break;
276	1.38M	}
277	1.38M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC