1 /* vi: set sw=4 ts=4: */
2 /*
3 * Utility routines.
4 *
5 * Copyright (C) 2008 Denys Vlasenko
6 *
7 * Licensed under GPLv2, see file LICENSE in this source tree.
8 */
9 #include "libbb.h"
10
11 /* Resize (grow) malloced vector.
12 *
13 * #define magic packed two parameters into one:
14 * sizeof = sizeof_and_shift >> 8
15 * shift = (sizeof_and_shift) & 0xff
16 *
17 * Lets say shift = 4. 1 << 4 == 0x10.
18 * If idx == 0, 0x10, 0x20 etc, vector[] is resized to next higher
19 * idx step, plus one: if idx == 0x20, vector[] is resized to 0x31,
20 * thus last usable element is vector[0x30].
21 *
22 * In other words: after xrealloc_vector(v, 4, idx), with any idx,
23 * it's ok to use at least v[idx] and v[idx+1].
24 * v[idx+2] etc generally are not ok.
25 *
26 * New elements are zeroed out, but only if realloc was done
27 * (not on every call). You can depend on v[idx] and v[idx+1] being
28 * zeroed out if you use it like this:
29 * v = xrealloc_vector(v, 4, idx);
30 * v[idx].some_fields = ...; - the rest stays 0/NULL
31 * idx++;
32 * If you do not advance idx like above, you should be more careful.
33 * Next call to xrealloc_vector(v, 4, idx) may or may not zero out v[idx].
34 */
xrealloc_vector_helper(void * vector,unsigned sizeof_and_shift,int idx)35 void* FAST_FUNC xrealloc_vector_helper(void *vector, unsigned sizeof_and_shift, int idx)
36 {
37 int mask = 1 << (uint8_t)sizeof_and_shift;
38
39 if (!(idx & (mask - 1))) {
40 sizeof_and_shift >>= 8; /* sizeof(vector[0]) */
41 vector = xrealloc(vector, sizeof_and_shift * (idx + mask + 1));
42 memset((char*)vector + (sizeof_and_shift * idx), 0, sizeof_and_shift * (mask + 1));
43 }
44 return vector;
45 }
46