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