/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: 2025-01-28 06:58

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	77.9k	{
49	77.9k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	459k	{
51	459k	if (COMPARE (src1, src2) <= 0)
52	399k	{
53	399k	dst++ = src1++;
54	399k	n1--;
55	399k	if (n1 == 0)
56	74.1k	break;
57	399k	}
58	60.3k	else
59	60.3k	{
60	60.3k	dst++ = src2++;
61	60.3k	n2--;
62	60.3k	if (n2 == 0)
63	3.83k	break;
64	60.3k	}
65	459k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	77.9k	if (n1 > 0)
68	3.83k	{
69	3.83k	if (dst != src1)
70	3.83k	do
71	6.25k	{
72	6.25k	dst++ = src1++;
73	6.25k	n1--;
74	6.25k	}
75	6.25k	while (n1 > 0);
76	3.83k	}
77	74.1k	else /* n2 > 0 */
78	74.1k	{
79	74.1k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	74.1k	}
87	77.9k	}
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	134k	{
100	134k	switch (n)
101	134k	{
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	67.1k	case 2:
109		/* Trivial case. */
110	67.1k	if (COMPARE (&src[0], &src[1]) <= 0)
111	63.3k	{
112		/* src[0] <= src[1] */
113	63.3k	dst[0] = src[0];
114	63.3k	dst[1] = src[1];
115	63.3k	}
116	3.84k	else
117	3.84k	{
118	3.84k	dst[0] = src[1];
119	3.84k	dst[1] = src[0];
120	3.84k	}
121	67.1k	break;
122	10.8k	case 3:
123		/* Simple case. */
124	10.8k	if (COMPARE (&src[0], &src[1]) <= 0)
125	8.27k	{
126	8.27k	if (COMPARE (&src[1], &src[2]) <= 0)
127	6.00k	{
128		/* src[0] <= src[1] <= src[2] */
129	6.00k	dst[0] = src[0];
130	6.00k	dst[1] = src[1];
131	6.00k	dst[2] = src[2];
132	6.00k	}
133	2.27k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.42k	{
135		/* src[0] <= src[2] < src[1] */
136	1.42k	dst[0] = src[0];
137	1.42k	dst[1] = src[2];
138	1.42k	dst[2] = src[1];
139	1.42k	}
140	848	else
141	848	{
142		/* src[2] < src[0] <= src[1] */
143	848	dst[0] = src[2];
144	848	dst[1] = src[0];
145	848	dst[2] = src[1];
146	848	}
147	8.27k	}
148	2.52k	else
149	2.52k	{
150	2.52k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.00k	{
152		/* src[1] < src[0] <= src[2] */
153	1.00k	dst[0] = src[1];
154	1.00k	dst[1] = src[0];
155	1.00k	dst[2] = src[2];
156	1.00k	}
157	1.52k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	809	{
159		/* src[1] <= src[2] < src[0] */
160	809	dst[0] = src[1];
161	809	dst[1] = src[2];
162	809	dst[2] = src[0];
163	809	}
164	716	else
165	716	{
166		/* src[2] < src[1] < src[0] */
167	716	dst[0] = src[2];
168	716	dst[1] = src[1];
169	716	dst[2] = src[0];
170	716	}
171	2.52k	}
172	10.8k	break;
173	56.6k	default:
174	56.6k	{
175	56.6k	size_t n1 = n / 2;
176	56.6k	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	56.6k	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	56.6k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	56.6k	merge (tmp, n1, dst + n1, n2, dst);
184	56.6k	}
185	56.6k	break;
186	134k	}
187	134k	}
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	37.1k	{
194	37.1k	switch (n)
195	37.1k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	21.7k	case 2:
201		/* Trivial case. */
202	21.7k	if (COMPARE (&src[0], &src[1]) <= 0)
203	21.3k	{
204		/* src[0] <= src[1] */
205	21.3k	}
206	465	else
207	465	{
208	465	ELEMENT t = src[0];
209	465	src[0] = src[1];
210	465	src[1] = t;
211	465	}
212	21.7k	break;
213	5.43k	case 3:
214		/* Simple case. */
215	5.43k	if (COMPARE (&src[0], &src[1]) <= 0)
216	3.94k	{
217	3.94k	if (COMPARE (&src[1], &src[2]) <= 0)
218	3.40k	{
219		/* src[0] <= src[1] <= src[2] */
220	3.40k	}
221	545	else if (COMPARE (&src[0], &src[2]) <= 0)
222	265	{
223		/* src[0] <= src[2] < src[1] */
224	265	ELEMENT t = src[1];
225	265	src[1] = src[2];
226	265	src[2] = t;
227	265	}
228	280	else
229	280	{
230		/* src[2] < src[0] <= src[1] */
231	280	ELEMENT t = src[0];
232	280	src[0] = src[2];
233	280	src[2] = src[1];
234	280	src[1] = t;
235	280	}
236	3.94k	}
237	1.48k	else
238	1.48k	{
239	1.48k	if (COMPARE (&src[0], &src[2]) <= 0)
240	709	{
241		/* src[1] < src[0] <= src[2] */
242	709	ELEMENT t = src[0];
243	709	src[0] = src[1];
244	709	src[1] = t;
245	709	}
246	778	else if (COMPARE (&src[1], &src[2]) <= 0)
247	528	{
248		/* src[1] <= src[2] < src[0] */
249	528	ELEMENT t = src[0];
250	528	src[0] = src[1];
251	528	src[1] = src[2];
252	528	src[2] = t;
253	528	}
254	250	else
255	250	{
256		/* src[2] < src[1] < src[0] */
257	250	ELEMENT t = src[0];
258	250	src[0] = src[2];
259	250	src[2] = t;
260	250	}
261	1.48k	}
262	5.43k	break;
263	9.88k	default:
264	9.88k	{
265	9.88k	size_t n1 = n / 2;
266	9.88k	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	9.88k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	9.88k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	9.88k	merge (tmp, n1, src + n1, n2, src);
274	9.88k	}
275	9.88k	break;
276	37.1k	}
277	37.1k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC