tree 8b4e1f5f0dec87498f12e23e0a64f71c55bd1e82
parent 806c9588ef424af188c5afe3c0932acee131bd63
author Gilles Peskine <Gilles.Peskine@arm.com> 1668024524 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> 1668541627 +0100

Support negative zero as MPI test input

The bignum module does not officially support "negative zero" (an
mbedtls_mpi object with s=-1 and all limbs zero). However, we have a
history of bugs where a function that should produce an official
zero (with s=1), produces a negative zero in some circumstances. So it's
good to check that the bignum functions are robust when passed a negative
zero as input. And for that, we need a way to construct a negative zero
from test case arguments.

There are checks that functions don't produce negative zeros as output in
the test suite. Skip those checks if there's a negative zero input: we
don't want functions to _create_ negative zeros, but we don't mind if
they _propagate_ negative zeros.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>