This patch modifies the left-shift implementation to closely
align in interface and behaviour to the existing right-shift
method.
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
Compare a single-limb MPI with a multi-limb MPI. This is rather ad hoc, but
will be useful for mbedtls_mpi_core_random.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
The loop ends when there are no more bits to process, with one twist: when
that happens, we need to clear the window one last time. Since the window
does not start empty (E_limbs==0 is not supported), the loop always starts
with a non-empty window and some bits to process. So it's correct to move
the window clearing logic to the end of the loop. This lets us exit the loop
when the end of the exponent is reached.
It would be clearer not to do the final window clearing inside the loop, so
we wouldn't need to repeat the loop termination condition (end of exponent
reached) inside the loop. However, this requires duplicating the code to
clear the window. Empirically, this causes a significant code size increase,
even if the window clearing code is placed into a function.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
We are looking at the exponent at limb granularity and therefore
exponent bits can't go below 32.
The `mpi_` prefix is also removed as it is better not to have prefix at
all than to have just a partial. (Full prefix would be overly long and
would hurt readability.)
Signed-off-by: Janos Follath <janos.follath@arm.com>
Now that we have a function that calls
mbedtls_mpi_core_ct_uint_table_lookup(), the compiler won't complain if
we make it static.
Signed-off-by: Janos Follath <janos.follath@arm.com>
On platforms with size_t different from int, mismatch between size_t and
mpi_uint can cause incorrect results or complaints from the compiler.
Signed-off-by: Janos Follath <janos.follath@arm.com>
mpi_core_exp_mod: Cast local variable explicitly
Signed-off-by: Janos Follath <janos.follath@arm.com>
This will be needed for extracting modular exponentiation from the
prototype. The function signature is kept aligned to the prototype, but
the implementation is new. (The implementation of this function in the
prototype has further optimisations which are out of scope for now.)
The function is not reused in the bignum counterpart as it will become
redundant soon.
This function is meant to be static, but doesn't have the qualifier as
it is not used yet and would cause compiler warnings. The
MBEDTLS_STATIC_TESTABLE macro will be added in a later commit.
Signed-off-by: Janos Follath <janos.follath@arm.com>
