docs by Matt K

firmware/Makefile

@@ -30,6 +30,7 @@ endif
 
 # C++ specific options here (added to USE_OPT).
 ifeq ($(USE_CPPOPT),)
+  # constexpr float expf_taylor_impl probably needs just c++14 but why not go with 17?
   USE_CPPOPT = -std=c++17 -Wno-register -fno-rtti -fno-exceptions -fno-use-cxa-atexit -Werror=write-strings -Werror=type-limits
 endif
 

firmware/util/efilib.cpp

@@ -318,6 +318,10 @@ float limitRateOfChange(float newValue, float oldValue, float incrLimitPerSec, f
 
 constexpr float constant_e = 2.71828f;
 
+// 'constexpr' is a keyword that tells the compiler
+// "yes, this thing, it's a 'pure function' that only depends on its inputs and has no side effects"
+// like how const is a constant value, constexpr is a constant expression
+// so if somewhere you used it in a way that it could determine the exact arguments to the function at compile time, it will _run_ the function at compile time, and cook in the result as a constant
 constexpr float expf_taylor_impl(float x, uint8_t n)
 {
 	if (x < -2)