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47 lines
1.5 KiB
C
47 lines
1.5 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Utility routines.
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*
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* Copyright (C) 2008 Denys Vlasenko
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*
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* Licensed under GPLv2, see file LICENSE in this tarball for details.
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*/
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#include "libbb.h"
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/* Resize (grow) malloced vector.
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*
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* #define magic packed two parameters into one:
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* sizeof = sizeof_and_shift >> 8
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* shift = (sizeof_and_shift) & 0xff
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*
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* Lets say shift = 4. 1 << 4 == 0x10.
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* If idx == 0, 0x10, 0x20 etc, vector[] is resized to next higher
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* idx step, plus one: if idx == 0x20, vector[] is resized to 0x31,
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* thus last usable element is vector[0x30].
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*
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* In other words: after xrealloc_vector(v, 4, idx), with any idx,
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* it's ok to use at least v[idx] and v[idx+1].
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* v[idx+2] etc generally are not ok.
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*
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* New elements are zeroed out, but only if realloc was done
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* (not on every call). You can depend on v[idx] and v[idx+1] being
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* zeroed out if you use it like this:
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* v = xrealloc_vector(v, 4, idx);
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* v[idx].some_fields = ...; - the rest stays 0/NULL
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* idx++;
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* If you do not advance idx like above, you should be more careful.
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* Next call to xrealloc_vector(v, 4, idx) may or may not zero out v[idx].
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*/
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void* FAST_FUNC xrealloc_vector_helper(void *vector, unsigned sizeof_and_shift, int idx)
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{
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int mask = 1 << (uint8_t)sizeof_and_shift;
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if (!(idx & (mask - 1))) {
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sizeof_and_shift >>= 8; /* sizeof(vector[0]) */
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vector = xrealloc(vector, sizeof_and_shift * (idx + mask + 1));
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memset((char*)vector + (sizeof_and_shift * idx), 0, sizeof_and_shift * (mask + 1));
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}
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return vector;
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}
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