/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: 2025-11-08 07:07

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	660k	{
49	660k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.70M	{
51	9.70M	if (COMPARE (src1, src2) <= 0)
52	8.76M	{
53	8.76M	dst++ = src1++;
54	8.76M	n1--;
55	8.76M	if (n1 == 0)
56	655k	break;
57	8.76M	}
58	940k	else
59	940k	{
60	940k	dst++ = src2++;
61	940k	n2--;
62	940k	if (n2 == 0)
63	4.82k	break;
64	940k	}
65	9.70M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	660k	if (n1 > 0)
68	4.82k	{
69	4.82k	if (dst != src1)
70	4.82k	do
71	15.9k	{
72	15.9k	dst++ = src1++;
73	15.9k	n1--;
74	15.9k	}
75	15.9k	while (n1 > 0);
76	4.82k	}
77	655k	else /* n2 > 0 */
78	655k	{
79	655k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	655k	}
87	660k	}
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	1.29M	{
100	1.29M	switch (n)
101	1.29M	{
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	602k	case 2:
109		/* Trivial case. */
110	602k	if (COMPARE (&src[0], &src[1]) <= 0)
111	600k	{
112		/* src[0] <= src[1] */
113	600k	dst[0] = src[0];
114	600k	dst[1] = src[1];
115	600k	}
116	1.95k	else
117	1.95k	{
118	1.95k	dst[0] = src[1];
119	1.95k	dst[1] = src[0];
120	1.95k	}
121	602k	break;
122	58.5k	case 3:
123		/* Simple case. */
124	58.5k	if (COMPARE (&src[0], &src[1]) <= 0)
125	55.6k	{
126	55.6k	if (COMPARE (&src[1], &src[2]) <= 0)
127	53.1k	{
128		/* src[0] <= src[1] <= src[2] */
129	53.1k	dst[0] = src[0];
130	53.1k	dst[1] = src[1];
131	53.1k	dst[2] = src[2];
132	53.1k	}
133	2.50k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.63k	{
135		/* src[0] <= src[2] < src[1] */
136	1.63k	dst[0] = src[0];
137	1.63k	dst[1] = src[2];
138	1.63k	dst[2] = src[1];
139	1.63k	}
140	870	else
141	870	{
142		/* src[2] < src[0] <= src[1] */
143	870	dst[0] = src[2];
144	870	dst[1] = src[0];
145	870	dst[2] = src[1];
146	870	}
147	55.6k	}
148	2.89k	else
149	2.89k	{
150	2.89k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.25k	{
152		/* src[1] < src[0] <= src[2] */
153	1.25k	dst[0] = src[1];
154	1.25k	dst[1] = src[0];
155	1.25k	dst[2] = src[2];
156	1.25k	}
157	1.64k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	829	{
159		/* src[1] <= src[2] < src[0] */
160	829	dst[0] = src[1];
161	829	dst[1] = src[2];
162	829	dst[2] = src[0];
163	829	}
164	813	else
165	813	{
166		/* src[2] < src[1] < src[0] */
167	813	dst[0] = src[2];
168	813	dst[1] = src[1];
169	813	dst[2] = src[0];
170	813	}
171	2.89k	}
172	58.5k	break;
173	637k	default:
174	637k	{
175	637k	size_t n1 = n / 2;
176	637k	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	637k	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	637k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	637k	merge (tmp, n1, dst + n1, n2, dst);
184	637k	}
185	637k	break;
186	1.29M	}
187	1.29M	}
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	1.53M	{
194	1.53M	switch (n)
195	1.53M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.49M	case 2:
201		/* Trivial case. */
202	1.49M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.49M	{
204		/* src[0] <= src[1] */
205	1.49M	}
206	989	else
207	989	{
208	989	ELEMENT t = src[0];
209	989	src[0] = src[1];
210	989	src[1] = t;
211	989	}
212	1.49M	break;
213	17.0k	case 3:
214		/* Simple case. */
215	17.0k	if (COMPARE (&src[0], &src[1]) <= 0)
216	13.3k	{
217	13.3k	if (COMPARE (&src[1], &src[2]) <= 0)
218	10.9k	{
219		/* src[0] <= src[1] <= src[2] */
220	10.9k	}
221	2.35k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.30k	{
223		/* src[0] <= src[2] < src[1] */
224	1.30k	ELEMENT t = src[1];
225	1.30k	src[1] = src[2];
226	1.30k	src[2] = t;
227	1.30k	}
228	1.05k	else
229	1.05k	{
230		/* src[2] < src[0] <= src[1] */
231	1.05k	ELEMENT t = src[0];
232	1.05k	src[0] = src[2];
233	1.05k	src[2] = src[1];
234	1.05k	src[1] = t;
235	1.05k	}
236	13.3k	}
237	3.73k	else
238	3.73k	{
239	3.73k	if (COMPARE (&src[0], &src[2]) <= 0)
240	957	{
241		/* src[1] < src[0] <= src[2] */
242	957	ELEMENT t = src[0];
243	957	src[0] = src[1];
244	957	src[1] = t;
245	957	}
246	2.77k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.60k	{
248		/* src[1] <= src[2] < src[0] */
249	1.60k	ELEMENT t = src[0];
250	1.60k	src[0] = src[1];
251	1.60k	src[1] = src[2];
252	1.60k	src[2] = t;
253	1.60k	}
254	1.16k	else
255	1.16k	{
256		/* src[2] < src[1] < src[0] */
257	1.16k	ELEMENT t = src[0];
258	1.16k	src[0] = src[2];
259	1.16k	src[2] = t;
260	1.16k	}
261	3.73k	}
262	17.0k	break;
263	22.6k	default:
264	22.6k	{
265	22.6k	size_t n1 = n / 2;
266	22.6k	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	22.6k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	22.6k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	22.6k	merge (tmp, n1, src + n1, n2, src);
274	22.6k	}
275	22.6k	break;
276	1.53M	}
277	1.53M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC