[rc5] Risc speedup?

Carsten Jacobi carsten at jakes.kawo1.rwth-aachen.de
Sat Jul 19 20:09:44 EDT 1997


On 19-Jul-97 Remi Guyomarch wrote:
>Same for PowerPC : 601 is one-way but 603, 604 & 620 are two or three
>ways chips.

Small correction: 603 is one way too (ok, except a separate unit to load and
store). The 604 comes with two Integer Units for single-cycle instructions, and
one more for multiple-cycle instructions ... but surely it is not wrong to
compute two keys in one loop and interleave the instructions for the keys.

The problem with the rc5-algorithm is just, that it eats really many registers
on the RISC-machines. Also if the processor has 32 registers, almost all of them
are used up by the expanded key with 26 words. And than it is difficult to find
room for the second key to compute in the same loop (yes, there is still the
AMD 29k with 192 registers, but has someone a computer with this chip?).
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