> BTW, although malloc() returns a pointer "suitable aligned", that
> doesn't mean it is fast. The comment refers to the fact that some CPUs
> don't like fetching a long (say) except off a 4-byte boundary.
"Some CPUs"? It should say "all, but Intel", shouldn't it? And secondly
define "like." Even latest Intel CPUs like data being aligned on natural
boundaries. And when it comes to floating point data one should probably
say "love" instead of "like" as performance penalties of 25%-30% are
most common.
> In fact
> an x86 will fetch them on any alignment, so malloc() is not obliged to
> align at all,
I can't tell for all x86 OSes (especially Windows:-), but both Linux and
Solaris malloc()s do return 64 bit aligned pointers. They aren't
obliged, but they do.
> whereas for performance on an x86 you want to align on a
> paragraph boundary (16 bytes?).
??? Do you mean 80 bits floating point variables and SIMD (or whatever
they call it) extensions? Because otherwise just natural alignment (i.e.
short at 2 bytes, long at 4, double at 8, etc.) are as good as 16.
Andy.
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