[Cryptography] Exotic Operations in Primitive Construction
Jonathan Thornburg
jthorn4242 at gmail.com
Thu Oct 1 20:15:48 EDT 2020
John Denker <jsd at av8n.com> writes:
> It is hard to imagine a subtle bug in shift or rotate. (There are
> ways of misusing the instructions, but they're not subtle.)
On Thu, Oct 01, 2020 at 10:21:32AM -0700, Nemo wrote:
> Ever try left-shifting an int by 32 on x86? (Hint: x86 only uses the low
> 5 bits of the shift count.)
Another example: the Digital J-11 (a PDP-11 implementation used in
the PDP-11/73 and PDP-11/83 systems) had a microcode bug in the
arithmetic-shift instructions which caused a "left-shift by 31 bits"
instruction to actually execute a right-shift. See
http://simh.trailing-edge.com/docs/ucode_bugs.pdf
for details.
--
-- "Jonathan Thornburg [remove -animal to reply]" <jthorn at astro.indiana-zebra.edu>
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
currently on the west coast of Canada
Q: What's the differnece between a function and a subroutine?
A: Functions are integers you can call; Subroutines are arrays
that return to main. -- student in an introductory C/Fortran course
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