/src/gnutls/lib/unistring/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: 2026-11-12 06:28

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	87.2k	{
49	87.2k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	506k	{
51	506k	if (COMPARE (src1, src2) <= 0)
52	439k	{
53	439k	dst++ = src1++;
54	439k	n1--;
55	439k	if (n1 == 0)
56	82.6k	break;
57	439k	}
58	66.5k	else
59	66.5k	{
60	66.5k	dst++ = src2++;
61	66.5k	n2--;
62	66.5k	if (n2 == 0)
63	4.61k	break;
64	66.5k	}
65	506k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	87.2k	if (n1 > 0)
68	4.61k	{
69	4.61k	if (dst != src1)
70	4.61k	do
71	8.66k	{
72	8.66k	dst++ = src1++;
73	8.66k	n1--;
74	8.66k	}
75	8.66k	while (n1 > 0);
76	4.61k	}
77	82.6k	else /* n2 > 0 */
78	82.6k	{
79	82.6k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	82.6k	}
87	87.2k	}
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	149k	{
100	149k	switch (n)
101	149k	{
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	74.5k	case 2:
109		/* Trivial case. */
110	74.5k	if (COMPARE (&src[0], &src[1]) <= 0)
111	70.4k	{
112		/* src[0] <= src[1] */
113	70.4k	dst[0] = src[0];
114	70.4k	dst[1] = src[1];
115	70.4k	}
116	4.04k	else
117	4.04k	{
118	4.04k	dst[0] = src[1];
119	4.04k	dst[1] = src[0];
120	4.04k	}
121	74.5k	break;
122	12.7k	case 3:
123		/* Simple case. */
124	12.7k	if (COMPARE (&src[0], &src[1]) <= 0)
125	9.91k	{
126	9.91k	if (COMPARE (&src[1], &src[2]) <= 0)
127	7.31k	{
128		/* src[0] <= src[1] <= src[2] */
129	7.31k	dst[0] = src[0];
130	7.31k	dst[1] = src[1];
131	7.31k	dst[2] = src[2];
132	7.31k	}
133	2.59k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.72k	{
135		/* src[0] <= src[2] < src[1] */
136	1.72k	dst[0] = src[0];
137	1.72k	dst[1] = src[2];
138	1.72k	dst[2] = src[1];
139	1.72k	}
140	868	else
141	868	{
142		/* src[2] < src[0] <= src[1] */
143	868	dst[0] = src[2];
144	868	dst[1] = src[0];
145	868	dst[2] = src[1];
146	868	}
147	9.91k	}
148	2.82k	else
149	2.82k	{
150	2.82k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.20k	{
152		/* src[1] < src[0] <= src[2] */
153	1.20k	dst[0] = src[1];
154	1.20k	dst[1] = src[0];
155	1.20k	dst[2] = src[2];
156	1.20k	}
157	1.62k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	850	{
159		/* src[1] <= src[2] < src[0] */
160	850	dst[0] = src[1];
161	850	dst[1] = src[2];
162	850	dst[2] = src[0];
163	850	}
164	776	else
165	776	{
166		/* src[2] < src[1] < src[0] */
167	776	dst[0] = src[2];
168	776	dst[1] = src[1];
169	776	dst[2] = src[0];
170	776	}
171	2.82k	}
172	12.7k	break;
173	62.2k	default:
174	62.2k	{
175	62.2k	size_t n1 = n / 2;
176	62.2k	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	62.2k	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	62.2k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	62.2k	merge (tmp, n1, dst + n1, n2, dst);
184	62.2k	}
185	62.2k	break;
186	149k	}
187	149k	}
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	34.8k	{
194	34.8k	switch (n)
195	34.8k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	19.8k	case 2:
201		/* Trivial case. */
202	19.8k	if (COMPARE (&src[0], &src[1]) <= 0)
203	19.2k	{
204		/* src[0] <= src[1] */
205	19.2k	}
206	641	else
207	641	{
208	641	ELEMENT t = src[0];
209	641	src[0] = src[1];
210	641	src[1] = t;
211	641	}
212	19.8k	break;
213	5.31k	case 3:
214		/* Simple case. */
215	5.31k	if (COMPARE (&src[0], &src[1]) <= 0)
216	3.84k	{
217	3.84k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.20k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.20k	}
221	634	else if (COMPARE (&src[0], &src[2]) <= 0)
222	260	{
223		/* src[0] <= src[2] < src[1] */
224	260	ELEMENT t = src[1];
225	260	src[1] = src[2];
226	260	src[2] = t;
227	260	}
228	374	else
229	374	{
230		/* src[2] < src[0] <= src[1] */
231	374	ELEMENT t = src[0];
232	374	src[0] = src[2];
233	374	src[2] = src[1];
234	374	src[1] = t;
235	374	}
236	3.84k	}
237	1.47k	else
238	1.47k	{
239	1.47k	if (COMPARE (&src[0], &src[2]) <= 0)
240	544	{
241		/* src[1] < src[0] <= src[2] */
242	544	ELEMENT t = src[0];
243	544	src[0] = src[1];
244	544	src[1] = t;
245	544	}
246	932	else if (COMPARE (&src[1], &src[2]) <= 0)
247	673	{
248		/* src[1] <= src[2] < src[0] */
249	673	ELEMENT t = src[0];
250	673	src[0] = src[1];
251	673	src[1] = src[2];
252	673	src[2] = t;
253	673	}
254	259	else
255	259	{
256		/* src[2] < src[1] < src[0] */
257	259	ELEMENT t = src[0];
258	259	src[0] = src[2];
259	259	src[2] = t;
260	259	}
261	1.47k	}
262	5.31k	break;
263	9.63k	default:
264	9.63k	{
265	9.63k	size_t n1 = n / 2;
266	9.63k	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	9.63k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	9.63k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	9.63k	merge (tmp, n1, src + n1, n2, src);
274	9.63k	}
275	9.63k	break;
276	34.8k	}
277	34.8k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC