Disable 3-arg pow() function on m0 boards

jepler · jepler · commit c451b2225570 · 2020-11-24T16:54:33.000-06:00
`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.
diff --git a/ports/atmel-samd/mpconfigport.mk b/ports/atmel-samd/mpconfigport.mk
@@ -29,6 +29,10 @@ ifndef CIRCUITPY_AUDIOMP3
 CIRCUITPY_AUDIOMP3 = 0
 endif
 
+ifndef CIRCUITPY_BUILTINS_POW3
+CIRCUITPY_BUILTINS_POW3 = 0
+endif
+
 ifndef CIRCUITPY_FREQUENCYIO
 CIRCUITPY_FREQUENCYIO = 0
 endif
diff --git a/py/circuitpy_mpconfig.h b/py/circuitpy_mpconfig.h
@@ -184,7 +184,7 @@ typedef long mp_off_t;
 // Turning off FULL_BUILD removes some functionality to reduce flash size on tiny SAMD21s
 #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (CIRCUITPY_FULL_BUILD)
 #define MICROPY_CPYTHON_COMPAT                (CIRCUITPY_FULL_BUILD)
-#define MICROPY_PY_BUILTINS_POW3              (CIRCUITPY_FULL_BUILD)
+#define MICROPY_PY_BUILTINS_POW3              (CIRCUITPY_BUILTINS_POW3)
 #define MICROPY_COMP_FSTRING_LITERAL          (MICROPY_CPYTHON_COMPAT)
 #define MICROPY_MODULE_WEAK_LINKS             (0)
 #define MICROPY_PY_ALL_SPECIAL_METHODS        (CIRCUITPY_FULL_BUILD)
diff --git a/py/circuitpy_mpconfig.mk b/py/circuitpy_mpconfig.mk
@@ -90,6 +90,9 @@ CFLAGS += -DCIRCUITPY_BLEIO=$(CIRCUITPY_BLEIO)
 CIRCUITPY_BOARD ?= 1
 CFLAGS += -DCIRCUITPY_BOARD=$(CIRCUITPY_BOARD)
 
+CIRCUITPY_BUILTINS_POW3 ?= $(CIRCUITPY_FULL_BUILD)
+CFLAGS += -DCIRCUITPY_BUILTINS_POW3=$(CIRCUITPY_BUILTINS_POW3)
+
 CIRCUITPY_BUSIO ?= 1
 CFLAGS += -DCIRCUITPY_BUSIO=$(CIRCUITPY_BUSIO)
 
