/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: 2026-05-16 06:55

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	79.9k	{
49	79.9k	for (;;) /* while (n1 > 0 && n2 > 0) */
50	470k	{
51	470k	if (COMPARE (src1, src2) <= 0)
52	398k	{
53	398k	dst++ = src1++;
54	398k	n1--;
55	398k	if (n1 == 0)
56	74.7k	break;
57	398k	}
58	72.0k	else
59	72.0k	{
60	72.0k	dst++ = src2++;
61	72.0k	n2--;
62	72.0k	if (n2 == 0)
63	5.20k	break;
64	72.0k	}
65	470k	}
66		/* Here n1 == 0 \|\| n2 == 0 but also n1 > 0 \|\| n2 > 0. */
67	79.9k	if (n1 > 0)
68	5.20k	{
69	5.20k	if (dst != src1)
70	5.20k	do
71	9.56k	{
72	9.56k	dst++ = src1++;
73	9.56k	n1--;
74	9.56k	}
75	9.56k	while (n1 > 0);
76	5.20k	}
77	74.7k	else /* n2 > 0 */
78	74.7k	{
79	74.7k	if (dst != src2)
80	0	do
81	0	{
82	0	dst++ = src2++;
83	0	n2--;
84	0	}
85	0	while (n2 > 0);
86	74.7k	}
87	79.9k	}
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	137k	{
100	137k	switch (n)
101	137k	{
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	68.5k	case 2:
109		/* Trivial case. */
110	68.5k	if (COMPARE (&src[0], &src[1]) <= 0)
111	63.1k	{
112		/* src[0] <= src[1] */
113	63.1k	dst[0] = src[0];
114	63.1k	dst[1] = src[1];
115	63.1k	}
116	5.40k	else
117	5.40k	{
118	5.40k	dst[0] = src[1];
119	5.40k	dst[1] = src[0];
120	5.40k	}
121	68.5k	break;
122	11.4k	case 3:
123		/* Simple case. */
124	11.4k	if (COMPARE (&src[0], &src[1]) <= 0)
125	8.69k	{
126	8.69k	if (COMPARE (&src[1], &src[2]) <= 0)
127	6.21k	{
128		/* src[0] <= src[1] <= src[2] */
129	6.21k	dst[0] = src[0];
130	6.21k	dst[1] = src[1];
131	6.21k	dst[2] = src[2];
132	6.21k	}
133	2.48k	else if (COMPARE (&src[0], &src[2]) <= 0)
134	1.49k	{
135		/* src[0] <= src[2] < src[1] */
136	1.49k	dst[0] = src[0];
137	1.49k	dst[1] = src[2];
138	1.49k	dst[2] = src[1];
139	1.49k	}
140	986	else
141	986	{
142		/* src[2] < src[0] <= src[1] */
143	986	dst[0] = src[2];
144	986	dst[1] = src[0];
145	986	dst[2] = src[1];
146	986	}
147	8.69k	}
148	2.74k	else
149	2.74k	{
150	2.74k	if (COMPARE (&src[0], &src[2]) <= 0)
151	1.16k	{
152		/* src[1] < src[0] <= src[2] */
153	1.16k	dst[0] = src[1];
154	1.16k	dst[1] = src[0];
155	1.16k	dst[2] = src[2];
156	1.16k	}
157	1.58k	else if (COMPARE (&src[1], &src[2]) <= 0)
158	846	{
159		/* src[1] <= src[2] < src[0] */
160	846	dst[0] = src[1];
161	846	dst[1] = src[2];
162	846	dst[2] = src[0];
163	846	}
164	735	else
165	735	{
166		/* src[2] < src[1] < src[0] */
167	735	dst[0] = src[2];
168	735	dst[1] = src[1];
169	735	dst[2] = src[0];
170	735	}
171	2.74k	}
172	11.4k	break;
173	58.0k	default:
174	58.0k	{
175	58.0k	size_t n1 = n / 2;
176	58.0k	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	58.0k	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	58.0k	merge_sort_fromto (src, tmp, n1, dst);
182		/* Merge the two half results. */
183	58.0k	merge (tmp, n1, dst + n1, n2, dst);
184	58.0k	}
185	58.0k	break;
186	137k	}
187	137k	}
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	113k	{
194	113k	switch (n)
195	113k	{
196	0	case 0:
197	0	case 1:
198		/* Nothing to do. */
199	0	return;
200	95.1k	case 2:
201		/* Trivial case. */
202	95.1k	if (COMPARE (&src[0], &src[1]) <= 0)
203	94.4k	{
204		/* src[0] <= src[1] */
205	94.4k	}
206	705	else
207	705	{
208	705	ELEMENT t = src[0];
209	705	src[0] = src[1];
210	705	src[1] = t;
211	705	}
212	95.1k	break;
213	7.03k	case 3:
214		/* Simple case. */
215	7.03k	if (COMPARE (&src[0], &src[1]) <= 0)
216	5.29k	{
217	5.29k	if (COMPARE (&src[1], &src[2]) <= 0)
218	4.11k	{
219		/* src[0] <= src[1] <= src[2] */
220	4.11k	}
221	1.17k	else if (COMPARE (&src[0], &src[2]) <= 0)
222	608	{
223		/* src[0] <= src[2] < src[1] */
224	608	ELEMENT t = src[1];
225	608	src[1] = src[2];
226	608	src[2] = t;
227	608	}
228	571	else
229	571	{
230		/* src[2] < src[0] <= src[1] */
231	571	ELEMENT t = src[0];
232	571	src[0] = src[2];
233	571	src[2] = src[1];
234	571	src[1] = t;
235	571	}
236	5.29k	}
237	1.74k	else
238	1.74k	{
239	1.74k	if (COMPARE (&src[0], &src[2]) <= 0)
240	692	{
241		/* src[1] < src[0] <= src[2] */
242	692	ELEMENT t = src[0];
243	692	src[0] = src[1];
244	692	src[1] = t;
245	692	}
246	1.05k	else if (COMPARE (&src[1], &src[2]) <= 0)
247	573	{
248		/* src[1] <= src[2] < src[0] */
249	573	ELEMENT t = src[0];
250	573	src[0] = src[1];
251	573	src[1] = src[2];
252	573	src[2] = t;
253	573	}
254	480	else
255	480	{
256		/* src[2] < src[1] < src[0] */
257	480	ELEMENT t = src[0];
258	480	src[0] = src[2];
259	480	src[2] = t;
260	480	}
261	1.74k	}
262	7.03k	break;
263	10.9k	default:
264	10.9k	{
265	10.9k	size_t n1 = n / 2;
266	10.9k	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	10.9k	merge_sort_inplace (src + n1, n2, tmp);
270		/* Sort src[0..n1-1] into tmp[0..n1-1], scratching tmp[n1..2n1-1]. /
271	10.9k	merge_sort_fromto (src, tmp, n1, tmp + n1);
272		/* Merge the two half results. */
273	10.9k	merge (tmp, n1, src + n1, n2, src);
274	10.9k	}
275	10.9k	break;
276	113k	}
277	113k	}
278
279		#undef ELEMENT
280		#undef COMPARE
281		#undef STATIC