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

Source
/* 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: 2025-11-16 06:46

Line	Count	Source
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	17.7k	{
49	17.7k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	93.7k	{
51	93.7k	if (COMPARE (src1, src2) <= 0)
52	81.4k	{
53	81.4k	dst++ = src1++;
54	81.4k	n1--;
55	81.4k	if (n1 == 0)
56	16.5k	break;
57	81.4k	}
58	12.2k	else
59	12.2k	{
60	12.2k	dst++ = src2++;
61	12.2k	n2--;
62	12.2k	if (n2 == 0)
63	1.19k	break;
64	12.2k	}
65	93.7k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	17.7k	if (n1 > 0)
68	1.19k	{
69	1.19k	if (dst != src1)
70	1.19k	do
71	1.99k	{
72	1.99k	dst++ = src1++;
73	1.99k	n1--;
74	1.99k	}
75	1.99k	while (n1 > 0);
76	1.19k	}
77	16.5k	else /* n2 > 0 */
78	16.5k	{
79	16.5k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	16.5k	}
87	17.7k	}
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	28.3k	{
100	28.3k	switch (n)
101	28.3k	{
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	14.5k	case 2:
109		/* Trivial case. */
110	14.5k	if (COMPARE (&src[0], &src[1]) <= 0)
111	13.8k	{
112		/* src[0] <= src[1] */
113	13.8k	dst[0] = src[0];
114	13.8k	dst[1] = src[1];
115	13.8k	}
116	673	else
117	673	{
118	673	dst[0] = src[1];
119	673	dst[1] = src[0];
120	673	}
121	14.5k	break;
122	3.28k	case 3:
123		/* Simple case. */
124	3.28k	if (COMPARE (&src[0], &src[1]) <= 0)
125	2.73k	{
126	2.73k	if (COMPARE (&src[1], &src[2]) <= 0)
127	2.26k	{
128		/* src[0] <= src[1] <= src[2] */
129	2.26k	dst[0] = src[0];
130	2.26k	dst[1] = src[1];
131	2.26k	dst[2] = src[2];
132	2.26k	}
133	474	else if (COMPARE (&src[0], &src[2]) <= 0)
134	262	{
135		/* src[0] <= src[2] < src[1] */
136	262	dst[0] = src[0];
137	262	dst[1] = src[2];
138	262	dst[2] = src[1];
139	262	}
140	212	else
141	212	{
142		/* src[2] < src[0] <= src[1] */
143	212	dst[0] = src[2];
144	212	dst[1] = src[0];
145	212	dst[2] = src[1];
146	212	}
147	2.73k	}
148	546	else
149	546	{
150	546	if (COMPARE (&src[0], &src[2]) <= 0)
151	235	{
152		/* src[1] < src[0] <= src[2] */
153	235	dst[0] = src[1];
154	235	dst[1] = src[0];
155	235	dst[2] = src[2];
156	235	}
157	311	else if (COMPARE (&src[1], &src[2]) <= 0)
158	231	{
159		/* src[1] <= src[2] < src[0] */
160	231	dst[0] = src[1];
161	231	dst[1] = src[2];
162	231	dst[2] = src[0];
163	231	}
164	80	else
165	80	{
166		/* src[2] < src[1] < src[0] */
167	80	dst[0] = src[2];
168	80	dst[1] = src[1];
169	80	dst[2] = src[0];
170	80	}
171	546	}
172	3.28k	break;
173	10.5k	default:
174	10.5k	{
175	10.5k	size_t n1 = n / 2;
176	10.5k	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	10.5k	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	10.5k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	10.5k	merge (tmp, n1, dst + n1, n2, dst);
184	10.5k	}
185	10.5k	break;
186	28.3k	}
187	28.3k	}
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	19.1k	{
194	19.1k	switch (n)
195	19.1k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	6.87k	case 2:
201		/* Trivial case. */
202	6.87k	if (COMPARE (&src[0], &src[1]) <= 0)
203	6.61k	{
204		/* src[0] <= src[1] */
205	6.61k	}
206	268	else
207	268	{
208	268	ELEMENT t = src[0];
209	268	src[0] = src[1];
210	268	src[1] = t;
211	268	}
212	6.87k	break;
213	4.98k	case 3:
214		/* Simple case. */
215	4.98k	if (COMPARE (&src[0], &src[1]) <= 0)
216	3.54k	{
217	3.54k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.02k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.02k	}
221	522	else if (COMPARE (&src[0], &src[2]) <= 0)
222	236	{
223		/* src[0] <= src[2] < src[1] */
224	236	ELEMENT t = src[1];
225	236	src[1] = src[2];
226	236	src[2] = t;
227	236	}
228	286	else
229	286	{
230		/* src[2] < src[0] <= src[1] */
231	286	ELEMENT t = src[0];
232	286	src[0] = src[2];
233	286	src[2] = src[1];
234	286	src[1] = t;
235	286	}
236	3.54k	}
237	1.44k	else
238	1.44k	{
239	1.44k	if (COMPARE (&src[0], &src[2]) <= 0)
240	521	{
241		/* src[1] < src[0] <= src[2] */
242	521	ELEMENT t = src[0];
243	521	src[0] = src[1];
244	521	src[1] = t;
245	521	}
246	924	else if (COMPARE (&src[1], &src[2]) <= 0)
247	704	{
248		/* src[1] <= src[2] < src[0] */
249	704	ELEMENT t = src[0];
250	704	src[0] = src[1];
251	704	src[1] = src[2];
252	704	src[2] = t;
253	704	}
254	220	else
255	220	{
256		/* src[2] < src[1] < src[0] */
257	220	ELEMENT t = src[0];
258	220	src[0] = src[2];
259	220	src[2] = t;
260	220	}
261	1.44k	}
262	4.98k	break;
263	7.25k	default:
264	7.25k	{
265	7.25k	size_t n1 = n / 2;
266	7.25k	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	7.25k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	7.25k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	7.25k	merge (tmp, n1, src + n1, n2, src);
274	7.25k	}
275	7.25k	break;
276	19.1k	}
277	19.1k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC