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

Source
/* Stable-sorting of an array using mergesort.
   Copyright (C) 2009-2026 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: 2026-01-06 07:18

Line	Count	Source
1		/* Stable-sorting of an array using mergesort.
2		Copyright (C) 2009-2026 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	697k	{
49	697k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	10.2M	{
51	10.2M	if (COMPARE (src1, src2) <= 0)
52	9.14M	{
53	9.14M	dst++ = src1++;
54	9.14M	n1--;
55	9.14M	if (n1 == 0)
56	692k	break;
57	9.14M	}
58	1.08M	else
59	1.08M	{
60	1.08M	dst++ = src2++;
61	1.08M	n2--;
62	1.08M	if (n2 == 0)
63	5.44k	break;
64	1.08M	}
65	10.2M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	697k	if (n1 > 0)
68	5.44k	{
69	5.44k	if (dst != src1)
70	5.44k	do
71	15.9k	{
72	15.9k	dst++ = src1++;
73	15.9k	n1--;
74	15.9k	}
75	15.9k	while (n1 > 0);
76	5.44k	}
77	692k	else /* n2 > 0 */
78	692k	{
79	692k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	692k	}
87	697k	}
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	1.37M	{
100	1.37M	switch (n)
101	1.37M	{
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	634k	case 2:
109		/* Trivial case. */
110	634k	if (COMPARE (&src[0], &src[1]) <= 0)
111	632k	{
112		/* src[0] <= src[1] */
113	632k	dst[0] = src[0];
114	632k	dst[1] = src[1];
115	632k	}
116	2.51k	else
117	2.51k	{
118	2.51k	dst[0] = src[1];
119	2.51k	dst[1] = src[0];
120	2.51k	}
121	634k	break;
122	62.9k	case 3:
123		/* Simple case. */
124	62.9k	if (COMPARE (&src[0], &src[1]) <= 0)
125	59.3k	{
126	59.3k	if (COMPARE (&src[1], &src[2]) <= 0)
127	56.5k	{
128		/* src[0] <= src[1] <= src[2] */
129	56.5k	dst[0] = src[0];
130	56.5k	dst[1] = src[1];
131	56.5k	dst[2] = src[2];
132	56.5k	}
133	2.79k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.79k	{
135		/* src[0] <= src[2] < src[1] */
136	1.79k	dst[0] = src[0];
137	1.79k	dst[1] = src[2];
138	1.79k	dst[2] = src[1];
139	1.79k	}
140	1.00k	else
141	1.00k	{
142		/* src[2] < src[0] <= src[1] */
143	1.00k	dst[0] = src[2];
144	1.00k	dst[1] = src[0];
145	1.00k	dst[2] = src[1];
146	1.00k	}
147	59.3k	}
148	3.65k	else
149	3.65k	{
150	3.65k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.59k	{
152		/* src[1] < src[0] <= src[2] */
153	1.59k	dst[0] = src[1];
154	1.59k	dst[1] = src[0];
155	1.59k	dst[2] = src[2];
156	1.59k	}
157	2.06k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.37k	{
159		/* src[1] <= src[2] < src[0] */
160	1.37k	dst[0] = src[1];
161	1.37k	dst[1] = src[2];
162	1.37k	dst[2] = src[0];
163	1.37k	}
164	697	else
165	697	{
166		/* src[2] < src[1] < src[0] */
167	697	dst[0] = src[2];
168	697	dst[1] = src[1];
169	697	dst[2] = src[0];
170	697	}
171	3.65k	}
172	62.9k	break;
173	673k	default:
174	673k	{
175	673k	size_t n1 = n / 2;
176	673k	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	673k	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	673k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	673k	merge (tmp, n1, dst + n1, n2, dst);
184	673k	}
185	673k	break;
186	1.37M	}
187	1.37M	}
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	1.68M	{
194	1.68M	switch (n)
195	1.68M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.64M	case 2:
201		/* Trivial case. */
202	1.64M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.64M	{
204		/* src[0] <= src[1] */
205	1.64M	}
206	1.05k	else
207	1.05k	{
208	1.05k	ELEMENT t = src[0];
209	1.05k	src[0] = src[1];
210	1.05k	src[1] = t;
211	1.05k	}
212	1.64M	break;
213	17.2k	case 3:
214		/* Simple case. */
215	17.2k	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	2.41k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.19k	{
223		/* src[0] <= src[2] < src[1] */
224	1.19k	ELEMENT t = src[1];
225	1.19k	src[1] = src[2];
226	1.19k	src[2] = t;
227	1.19k	}
228	1.21k	else
229	1.21k	{
230		/* src[2] < src[0] <= src[1] */
231	1.21k	ELEMENT t = src[0];
232	1.21k	src[0] = src[2];
233	1.21k	src[2] = src[1];
234	1.21k	src[1] = t;
235	1.21k	}
236	13.3k	}
237	3.92k	else
238	3.92k	{
239	3.92k	if (COMPARE (&src[0], &src[2]) <= 0)
240	1.13k	{
241		/* src[1] < src[0] <= src[2] */
242	1.13k	ELEMENT t = src[0];
243	1.13k	src[0] = src[1];
244	1.13k	src[1] = t;
245	1.13k	}
246	2.78k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.74k	{
248		/* src[1] <= src[2] < src[0] */
249	1.74k	ELEMENT t = src[0];
250	1.74k	src[0] = src[1];
251	1.74k	src[1] = src[2];
252	1.74k	src[2] = t;
253	1.74k	}
254	1.03k	else
255	1.03k	{
256		/* src[2] < src[1] < src[0] */
257	1.03k	ELEMENT t = src[0];
258	1.03k	src[0] = src[2];
259	1.03k	src[2] = t;
260	1.03k	}
261	3.92k	}
262	17.2k	break;
263	23.7k	default:
264	23.7k	{
265	23.7k	size_t n1 = n / 2;
266	23.7k	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	23.7k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	23.7k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	23.7k	merge (tmp, n1, src + n1, n2, src);
274	23.7k	}
275	23.7k	break;
276	1.68M	}
277	1.68M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC