tree 64d589f4b4f28cd4cdd892d5b45d6878c5f28db0
parent cfd6d4181b92ab99d3a6024a76a8a2546aebfb74
author Rupert Swarbrick <rswarbrick@lowrisc.org> 1601624598 +0100
committer Rupert Swarbrick <rswarbrick@gmail.com> 1601630113 +0100

[otbn] Fix rounding in bn.addm in ISS

The add_with_carry function truncates its result to 256 bits, which is
what you normally want, but isn't what you want for BN.ADDM, where you
might overflow but then fix it by subtracting MOD.

I've updated the documentation to match. This now matches the RTL.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>