/src/gnutls/lib/unistring/array-mergesort.h

Source (jump to first uncovered line)
/* 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: 2025-07-23 07:18

Line	Count	Source (jump to first uncovered line)
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	73.9k	{
49	73.9k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	439k	{
51	439k	if (COMPARE (src1, src2) <= 0)
52	379k	{
53	379k	dst++ = src1++;
54	379k	n1--;
55	379k	if (n1 == 0)
56	70.2k	break;
57	379k	}
58	59.1k	else
59	59.1k	{
60	59.1k	dst++ = src2++;
61	59.1k	n2--;
62	59.1k	if (n2 == 0)
63	3.68k	break;
64	59.1k	}
65	439k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	73.9k	if (n1 > 0)
68	3.68k	{
69	3.68k	if (dst != src1)
70	3.68k	do
71	6.32k	{
72	6.32k	dst++ = src1++;
73	6.32k	n1--;
74	6.32k	}
75	6.32k	while (n1 > 0);
76	3.68k	}
77	70.2k	else /* n2 > 0 */
78	70.2k	{
79	70.2k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	70.2k	}
87	73.9k	}
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	128k	{
100	128k	switch (n)
101	128k	{
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	63.6k	case 2:
109		/* Trivial case. */
110	63.6k	if (COMPARE (&src[0], &src[1]) <= 0)
111	59.4k	{
112		/* src[0] <= src[1] */
113	59.4k	dst[0] = src[0];
114	59.4k	dst[1] = src[1];
115	59.4k	}
116	4.15k	else
117	4.15k	{
118	4.15k	dst[0] = src[1];
119	4.15k	dst[1] = src[0];
120	4.15k	}
121	63.6k	break;
122	10.3k	case 3:
123		/* Simple case. */
124	10.3k	if (COMPARE (&src[0], &src[1]) <= 0)
125	7.75k	{
126	7.75k	if (COMPARE (&src[1], &src[2]) <= 0)
127	5.56k	{
128		/* src[0] <= src[1] <= src[2] */
129	5.56k	dst[0] = src[0];
130	5.56k	dst[1] = src[1];
131	5.56k	dst[2] = src[2];
132	5.56k	}
133	2.18k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.39k	{
135		/* src[0] <= src[2] < src[1] */
136	1.39k	dst[0] = src[0];
137	1.39k	dst[1] = src[2];
138	1.39k	dst[2] = src[1];
139	1.39k	}
140	789	else
141	789	{
142		/* src[2] < src[0] <= src[1] */
143	789	dst[0] = src[2];
144	789	dst[1] = src[0];
145	789	dst[2] = src[1];
146	789	}
147	7.75k	}
148	2.58k	else
149	2.58k	{
150	2.58k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.10k	{
152		/* src[1] < src[0] <= src[2] */
153	1.10k	dst[0] = src[1];
154	1.10k	dst[1] = src[0];
155	1.10k	dst[2] = src[2];
156	1.10k	}
157	1.47k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	761	{
159		/* src[1] <= src[2] < src[0] */
160	761	dst[0] = src[1];
161	761	dst[1] = src[2];
162	761	dst[2] = src[0];
163	761	}
164	710	else
165	710	{
166		/* src[2] < src[1] < src[0] */
167	710	dst[0] = src[2];
168	710	dst[1] = src[1];
169	710	dst[2] = src[0];
170	710	}
171	2.58k	}
172	10.3k	break;
173	54.2k	default:
174	54.2k	{
175	54.2k	size_t n1 = n / 2;
176	54.2k	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	54.2k	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	54.2k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	54.2k	merge (tmp, n1, dst + n1, n2, dst);
184	54.2k	}
185	54.2k	break;
186	128k	}
187	128k	}
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	39.7k	{
194	39.7k	switch (n)
195	39.7k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	24.7k	case 2:
201		/* Trivial case. */
202	24.7k	if (COMPARE (&src[0], &src[1]) <= 0)
203	24.2k	{
204		/* src[0] <= src[1] */
205	24.2k	}
206	502	else
207	502	{
208	502	ELEMENT t = src[0];
209	502	src[0] = src[1];
210	502	src[1] = t;
211	502	}
212	24.7k	break;
213	5.77k	case 3:
214		/* Simple case. */
215	5.77k	if (COMPARE (&src[0], &src[1]) <= 0)
216	4.50k	{
217	4.50k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.92k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.92k	}
221	583	else if (COMPARE (&src[0], &src[2]) <= 0)
222	258	{
223		/* src[0] <= src[2] < src[1] */
224	258	ELEMENT t = src[1];
225	258	src[1] = src[2];
226	258	src[2] = t;
227	258	}
228	325	else
229	325	{
230		/* src[2] < src[0] <= src[1] */
231	325	ELEMENT t = src[0];
232	325	src[0] = src[2];
233	325	src[2] = src[1];
234	325	src[1] = t;
235	325	}
236	4.50k	}
237	1.27k	else
238	1.27k	{
239	1.27k	if (COMPARE (&src[0], &src[2]) <= 0)
240	535	{
241		/* src[1] < src[0] <= src[2] */
242	535	ELEMENT t = src[0];
243	535	src[0] = src[1];
244	535	src[1] = t;
245	535	}
246	738	else if (COMPARE (&src[1], &src[2]) <= 0)
247	492	{
248		/* src[1] <= src[2] < src[0] */
249	492	ELEMENT t = src[0];
250	492	src[0] = src[1];
251	492	src[1] = src[2];
252	492	src[2] = t;
253	492	}
254	246	else
255	246	{
256		/* src[2] < src[1] < src[0] */
257	246	ELEMENT t = src[0];
258	246	src[0] = src[2];
259	246	src[2] = t;
260	246	}
261	1.27k	}
262	5.77k	break;
263	9.30k	default:
264	9.30k	{
265	9.30k	size_t n1 = n / 2;
266	9.30k	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	9.30k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	9.30k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	9.30k	merge (tmp, n1, src + n1, n2, src);
274	9.30k	}
275	9.30k	break;
276	39.7k	}
277	39.7k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC