`pow(a, b, c)` can compute `(a ** b) % c` efficiently (in time and memory).
This can be useful for extremely specific applications, like implementing
the RSA cryptosystem. For typical uses of CircuitPython, this is not an
important feature. A survey of the bundle and learn system didn't find
any uses.
Disable it on M0 builds so that we can fit in needed upgrades to the USB
stack.
Instead of unrolling the code 16 times, unroll it 4 times and loop
over it 4 times. This gives the same 16 iterations, but at an expense
of less flash space.
This reclaims over 1kB of flash space by simplifying certain exception
messages. e.g., it will no longer display the requested/actual length
when a fixed list/tuple of N items is needed:
if (MICROPY_ERROR_REPORTING == MICROPY_ERROR_REPORTING_TERSE) {
mp_raise_ValueError(translate("tuple/list has wrong length"));
} else {
mp_raise_ValueError_varg(translate("requested length %d but object has length %d"),
(int)len, (int)seq_len);
Other chip families including samd51 keep their current error reporting
capabilities.
* No weak link for modules. It only impacts _os and _time and is
already disabled for non-full builds.
* Turn off PA00 and PA01 because they are the crystal on the Metro
M0 Express.
* Change ejected default to false to move it to BSS. It is set on
USB connection anyway.
* Set sinc_filter to const. Doesn't help flash but keeps it out of
RAM.
This decreases the link time, especially on desktop machines with many CPU
cores. However, it does come at a slight cost in binary size, making the flash
section about 200 bytes bigger for circuitplayground_express.
Before, linking build-circuitplayground_express/firmware.elf takes
8.8s elapsed time, leaving 3128 bytes free in flash.
After, linking build-circuitplayground_express/firmware.elf takes 2.8s elapsed
time, leaving 2924 bytes free in flash. (-6 seconds, -204 bytes free)
If necessary, we can make this per-board or even per-translation to squeeze full
builds.
