/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: 2025-10-26 06:49

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	672k	{
49	672k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.81M	{
51	9.81M	if (COMPARE (src1, src2) <= 0)
52	8.86M	{
53	8.86M	dst++ = src1++;
54	8.86M	n1--;
55	8.86M	if (n1 == 0)
56	666k	break;
57	8.86M	}
58	946k	else
59	946k	{
60	946k	dst++ = src2++;
61	946k	n2--;
62	946k	if (n2 == 0)
63	5.91k	break;
64	946k	}
65	9.81M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	672k	if (n1 > 0)
68	5.91k	{
69	5.91k	if (dst != src1)
70	5.91k	do
71	17.1k	{
72	17.1k	dst++ = src1++;
73	17.1k	n1--;
74	17.1k	}
75	17.1k	while (n1 > 0);
76	5.91k	}
77	666k	else /* n2 > 0 */
78	666k	{
79	666k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	666k	}
87	672k	}
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	1.31M	{
100	1.31M	switch (n)
101	1.31M	{
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	605k	case 2:
109		/* Trivial case. */
110	605k	if (COMPARE (&src[0], &src[1]) <= 0)
111	602k	{
112		/* src[0] <= src[1] */
113	602k	dst[0] = src[0];
114	602k	dst[1] = src[1];
115	602k	}
116	3.10k	else
117	3.10k	{
118	3.10k	dst[0] = src[1];
119	3.10k	dst[1] = src[0];
120	3.10k	}
121	605k	break;
122	66.1k	case 3:
123		/* Simple case. */
124	66.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	62.1k	{
126	62.1k	if (COMPARE (&src[1], &src[2]) <= 0)
127	58.9k	{
128		/* src[0] <= src[1] <= src[2] */
129	58.9k	dst[0] = src[0];
130	58.9k	dst[1] = src[1];
131	58.9k	dst[2] = src[2];
132	58.9k	}
133	3.18k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.88k	{
135		/* src[0] <= src[2] < src[1] */
136	1.88k	dst[0] = src[0];
137	1.88k	dst[1] = src[2];
138	1.88k	dst[2] = src[1];
139	1.88k	}
140	1.30k	else
141	1.30k	{
142		/* src[2] < src[0] <= src[1] */
143	1.30k	dst[0] = src[2];
144	1.30k	dst[1] = src[0];
145	1.30k	dst[2] = src[1];
146	1.30k	}
147	62.1k	}
148	4.01k	else
149	4.01k	{
150	4.01k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.68k	{
152		/* src[1] < src[0] <= src[2] */
153	1.68k	dst[0] = src[1];
154	1.68k	dst[1] = src[0];
155	1.68k	dst[2] = src[2];
156	1.68k	}
157	2.32k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.46k	{
159		/* src[1] <= src[2] < src[0] */
160	1.46k	dst[0] = src[1];
161	1.46k	dst[1] = src[2];
162	1.46k	dst[2] = src[0];
163	1.46k	}
164	856	else
165	856	{
166		/* src[2] < src[1] < src[0] */
167	856	dst[0] = src[2];
168	856	dst[1] = src[1];
169	856	dst[2] = src[0];
170	856	}
171	4.01k	}
172	66.1k	break;
173	646k	default:
174	646k	{
175	646k	size_t n1 = n / 2;
176	646k	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	646k	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	646k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	646k	merge (tmp, n1, dst + n1, n2, dst);
184	646k	}
185	646k	break;
186	1.31M	}
187	1.31M	}
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	1.45M	{
194	1.45M	switch (n)
195	1.45M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.41M	case 2:
201		/* Trivial case. */
202	1.41M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.41M	{
204		/* src[0] <= src[1] */
205	1.41M	}
206	1.25k	else
207	1.25k	{
208	1.25k	ELEMENT t = src[0];
209	1.25k	src[0] = src[1];
210	1.25k	src[1] = t;
211	1.25k	}
212	1.41M	break;
213	18.3k	case 3:
214		/* Simple case. */
215	18.3k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.3k	{
217	14.3k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.3k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.3k	}
221	3.04k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.53k	{
223		/* src[0] <= src[2] < src[1] */
224	1.53k	ELEMENT t = src[1];
225	1.53k	src[1] = src[2];
226	1.53k	src[2] = t;
227	1.53k	}
228	1.51k	else
229	1.51k	{
230		/* src[2] < src[0] <= src[1] */
231	1.51k	ELEMENT t = src[0];
232	1.51k	src[0] = src[2];
233	1.51k	src[2] = src[1];
234	1.51k	src[1] = t;
235	1.51k	}
236	14.3k	}
237	3.95k	else
238	3.95k	{
239	3.95k	if (COMPARE (&src[0], &src[2]) <= 0)
240	978	{
241		/* src[1] < src[0] <= src[2] */
242	978	ELEMENT t = src[0];
243	978	src[0] = src[1];
244	978	src[1] = t;
245	978	}
246	2.97k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.62k	{
248		/* src[1] <= src[2] < src[0] */
249	1.62k	ELEMENT t = src[0];
250	1.62k	src[0] = src[1];
251	1.62k	src[1] = src[2];
252	1.62k	src[2] = t;
253	1.62k	}
254	1.35k	else
255	1.35k	{
256		/* src[2] < src[1] < src[0] */
257	1.35k	ELEMENT t = src[0];
258	1.35k	src[0] = src[2];
259	1.35k	src[2] = t;
260	1.35k	}
261	3.95k	}
262	18.3k	break;
263	25.6k	default:
264	25.6k	{
265	25.6k	size_t n1 = n / 2;
266	25.6k	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	25.6k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	25.6k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	25.6k	merge (tmp, n1, src + n1, n2, src);
274	25.6k	}
275	25.6k	break;
276	1.45M	}
277	1.45M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC