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-rw-r--r--libbb/xrealloc_vector.c14
1 files changed, 12 insertions, 2 deletions
diff --git a/libbb/xrealloc_vector.c b/libbb/xrealloc_vector.c
index ccc961b..342ae53 100644
--- a/libbb/xrealloc_vector.c
+++ b/libbb/xrealloc_vector.c
@@ -14,7 +14,6 @@
* #define magic packed two parameters into one:
* sizeof = sizeof_and_shift >> 8
* shift = (sizeof_and_shift) & 0xff
- * (TODO: encode "I want it zeroed" in lowest bit?)
*
* Lets say shift = 4. 1 << 4 == 0x10.
* If idx == 0, 0x10, 0x20 etc, vector[] is resized to next higher
@@ -23,14 +22,25 @@
*
* In other words: after xrealloc_vector(v, 4, idx) it's ok to use
* at least v[idx] and v[idx+1], for all idx values.
+ *
+ * New elements are zeroed out, but only if realloc was done
+ * (not on every call). You can depend on v[idx] and v[idx+1] being
+ * zeroed out if you use it like this:
+ * v = xrealloc_vector(v, 4, idx);
+ * v[idx].some_fields = ...; - the rest stays 0/NULL
+ * idx++;
+ * If you do not advance idx like above, you should be more careful.
+ * Next call to xrealloc_vector(v, 4, idx) may or may not zero out v[idx].
*/
void* FAST_FUNC xrealloc_vector_helper(void *vector, unsigned sizeof_and_shift, int idx)
{
int mask = 1 << (uint8_t)sizeof_and_shift;
if (!(idx & (mask - 1))) {
- sizeof_and_shift >>= 8;
+ sizeof_and_shift >>= 8; /* sizeof(vector[0]) */
vector = xrealloc(vector, sizeof_and_shift * (idx + mask + 1));
+ vector += idx;
+ memset(vector, 0, sizeof_and_shift * (mask + 1));
}
return vector;
}