/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: 2025-11-02 07:14

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	645k	{
49	645k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	9.54M	{
51	9.54M	if (COMPARE (src1, src2) <= 0)
52	8.55M	{
53	8.55M	dst++ = src1++;
54	8.55M	n1--;
55	8.55M	if (n1 == 0)
56	639k	break;
57	8.55M	}
58	986k	else
59	986k	{
60	986k	dst++ = src2++;
61	986k	n2--;
62	986k	if (n2 == 0)
63	6.26k	break;
64	986k	}
65	9.54M	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	645k	if (n1 > 0)
68	6.26k	{
69	6.26k	if (dst != src1)
70	6.26k	do
71	17.5k	{
72	17.5k	dst++ = src1++;
73	17.5k	n1--;
74	17.5k	}
75	17.5k	while (n1 > 0);
76	6.26k	}
77	639k	else /* n2 > 0 */
78	639k	{
79	639k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	639k	}
87	645k	}
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	1.26M	{
100	1.26M	switch (n)
101	1.26M	{
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	570k	case 2:
109		/* Trivial case. */
110	570k	if (COMPARE (&src[0], &src[1]) <= 0)
111	567k	{
112		/* src[0] <= src[1] */
113	567k	dst[0] = src[0];
114	567k	dst[1] = src[1];
115	567k	}
116	3.11k	else
117	3.11k	{
118	3.11k	dst[0] = src[1];
119	3.11k	dst[1] = src[0];
120	3.11k	}
121	570k	break;
122	75.1k	case 3:
123		/* Simple case. */
124	75.1k	if (COMPARE (&src[0], &src[1]) <= 0)
125	71.1k	{
126	71.1k	if (COMPARE (&src[1], &src[2]) <= 0)
127	67.8k	{
128		/* src[0] <= src[1] <= src[2] */
129	67.8k	dst[0] = src[0];
130	67.8k	dst[1] = src[1];
131	67.8k	dst[2] = src[2];
132	67.8k	}
133	3.24k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.93k	{
135		/* src[0] <= src[2] < src[1] */
136	1.93k	dst[0] = src[0];
137	1.93k	dst[1] = src[2];
138	1.93k	dst[2] = src[1];
139	1.93k	}
140	1.30k	else
141	1.30k	{
142		/* src[2] < src[0] <= src[1] */
143	1.30k	dst[0] = src[2];
144	1.30k	dst[1] = src[0];
145	1.30k	dst[2] = src[1];
146	1.30k	}
147	71.1k	}
148	4.05k	else
149	4.05k	{
150	4.05k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.73k	{
152		/* src[1] < src[0] <= src[2] */
153	1.73k	dst[0] = src[1];
154	1.73k	dst[1] = src[0];
155	1.73k	dst[2] = src[2];
156	1.73k	}
157	2.31k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	1.46k	{
159		/* src[1] <= src[2] < src[0] */
160	1.46k	dst[0] = src[1];
161	1.46k	dst[1] = src[2];
162	1.46k	dst[2] = src[0];
163	1.46k	}
164	855	else
165	855	{
166		/* src[2] < src[1] < src[0] */
167	855	dst[0] = src[2];
168	855	dst[1] = src[1];
169	855	dst[2] = src[0];
170	855	}
171	4.05k	}
172	75.1k	break;
173	619k	default:
174	619k	{
175	619k	size_t n1 = n / 2;
176	619k	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	619k	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	619k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	619k	merge (tmp, n1, dst + n1, n2, dst);
184	619k	}
185	619k	break;
186	1.26M	}
187	1.26M	}
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	1.55M	{
194	1.55M	switch (n)
195	1.55M	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	1.50M	case 2:
201		/* Trivial case. */
202	1.50M	if (COMPARE (&src[0], &src[1]) <= 0)
203	1.50M	{
204		/* src[0] <= src[1] */
205	1.50M	}
206	1.40k	else
207	1.40k	{
208	1.40k	ELEMENT t = src[0];
209	1.40k	src[0] = src[1];
210	1.40k	src[1] = t;
211	1.40k	}
212	1.50M	break;
213	19.3k	case 3:
214		/* Simple case. */
215	19.3k	if (COMPARE (&src[0], &src[1]) <= 0)
216	14.9k	{
217	14.9k	if (COMPARE (&src[1], &src[2]) <= 0)
218	11.4k	{
219		/* src[0] <= src[1] <= src[2] */
220	11.4k	}
221	3.46k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	1.86k	{
223		/* src[0] <= src[2] < src[1] */
224	1.86k	ELEMENT t = src[1];
225	1.86k	src[1] = src[2];
226	1.86k	src[2] = t;
227	1.86k	}
228	1.60k	else
229	1.60k	{
230		/* src[2] < src[0] <= src[1] */
231	1.60k	ELEMENT t = src[0];
232	1.60k	src[0] = src[2];
233	1.60k	src[2] = src[1];
234	1.60k	src[1] = t;
235	1.60k	}
236	14.9k	}
237	4.48k	else
238	4.48k	{
239	4.48k	if (COMPARE (&src[0], &src[2]) <= 0)
240	972	{
241		/* src[1] < src[0] <= src[2] */
242	972	ELEMENT t = src[0];
243	972	src[0] = src[1];
244	972	src[1] = t;
245	972	}
246	3.51k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	1.93k	{
248		/* src[1] <= src[2] < src[0] */
249	1.93k	ELEMENT t = src[0];
250	1.93k	src[0] = src[1];
251	1.93k	src[1] = src[2];
252	1.93k	src[2] = t;
253	1.93k	}
254	1.58k	else
255	1.58k	{
256		/* src[2] < src[1] < src[0] */
257	1.58k	ELEMENT t = src[0];
258	1.58k	src[0] = src[2];
259	1.58k	src[2] = t;
260	1.58k	}
261	4.48k	}
262	19.3k	break;
263	26.8k	default:
264	26.8k	{
265	26.8k	size_t n1 = n / 2;
266	26.8k	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	26.8k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	26.8k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	26.8k	merge (tmp, n1, src + n1, n2, src);
274	26.8k	}
275	26.8k	break;
276	1.55M	}
277	1.55M	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC