Previous to this patch bignum division and modulo would temporarily
modify the RHS argument to the operation (eg x/y would modify y), but on
return the RHS would be restored to its original value. This is not
allowed because arguments to binary operations are const, and in
particular might live in ROM. The modification was to normalise the arg
(and then unnormalise before returning), and this patch makes it so the
normalisation is done on the fly and the arg is now accessed as read-only.
This change doesn't increase the order complexity of the operation, and
actually reduces code size.
When DIG_SIZE=32, a uint32_t is used to store limbs, and no normalisation
is needed because the MSB is already set, then there will be left and
right shifts (in C) by 32 of a 32-bit variable, leading to undefined
behaviour. This patch fixes this bug.
This function computes (x**y)%z in an efficient way. For large arguments
this operation is otherwise not computable by doing x**y and then %z.
It's currently not used, but is added in case it's useful one day.
For these 3 bitwise operations there are now fast functions for
positive-only arguments, and general functions for arbitrary sign
arguments (the fast functions are the existing implementation).
By default the fast functions are not used (to save space) and instead
the general functions are used for all operations.
Enable MICROPY_OPT_MPZ_BITWISE to use the fast functions for positive
arguments.
Damien George
Doug Currie
Paul Sokolovsky
David Steinberg