Contents of /tags/mkinitrd-6_1_8/busybox/libbb/xrealloc_vector.c
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Wed Oct 28 00:17:50 2009 UTC (14 years, 11 months ago) by niro
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Wed Oct 28 00:17:50 2009 UTC (14 years, 11 months ago) by niro
File MIME type: text/plain
File size: 1501 byte(s)
tagged 'mkinitrd-6_1_8'
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 tarball for details. |
8 | */ |
9 | |
10 | #include "libbb.h" |
11 | |
12 | /* Resize (grow) malloced vector. |
13 | * |
14 | * #define magic packed two parameters into one: |
15 | * sizeof = sizeof_and_shift >> 8 |
16 | * shift = (sizeof_and_shift) & 0xff |
17 | * |
18 | * Lets say shift = 4. 1 << 4 == 0x10. |
19 | * If idx == 0, 0x10, 0x20 etc, vector[] is resized to next higher |
20 | * idx step, plus one: if idx == 0x20, vector[] is resized to 0x31, |
21 | * thus last usable element is vector[0x30]. |
22 | * |
23 | * In other words: after xrealloc_vector(v, 4, idx) it's ok to use |
24 | * at least v[idx] and v[idx+1], for all idx values. |
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 | */ |
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 | } |