Bug#324001: overlapping memcpy()
On 5/21/06, Thomas Dickey <dickey@radix.net> wrote:
On Sun, May 21, 2006 at 09:20:17AM +0200, Albert Cahalan wrote:
> That is indeed a serious error.
no - it's a stupid but benign error:
source and destination addresses are the same
Consider this entirely reasonable implementation for PowerPC:
if 32-byte aligned, do fast copy
else if 8-byte aligned do double copy
else if 4-byte aligned do float copy
else do byte copy
Then, for each 32-byte cache line, the "fast copy" code does:
1. prefetch the source cache line
2. allocate the destination cache line as all zeroes
3. fetch the source cache line
4. store the destination cache line
End result: it acts like bzero() when src==dst
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