Performing math functionality with #[no_std]

If you want to perform math related functionality like calculating the squareroot or the exponential of a number and you have the full standard library available, your code might look like this:

  1. //! Some mathematical functions with standard support available
  3. fn main() {
  4.     let float: f32 = 4.82832;
  5.     let floored_float = float.floor();
  7.     let sqrt_of_four = floored_float.sqrt();
  9.     let sinus_of_four = floored_float.sin();
  11.     let exponential_of_four = floored_float.exp();
  12.     println!("Floored test float {} to {}", float, floored_float);
  13.     println!("The square root of {} is {}", floored_float, sqrt_of_four);
  14.     println!("The sinus of four is {}", sinus_of_four);
  15.     println!(
  16.         "The exponential of four to the base e is {}",
  17.         exponential_of_four
  18.     )
  19. }

Without standard library support, these functions are not available. An external crate like libm can be used instead. The example code would then look like this:

  1. #![no_main]
  2. #![no_std]
  4. use panic_halt as _;
  6. use cortex_m_rt::entry;
  7. use cortex_m_semihosting::{debug, hprintln};
  8. use libm::{exp, floorf, sin, sqrtf};
  10. #[entry]
  11. fn main() -> ! {
  12.     let float = 4.82832;
  13.     let floored_float = floorf(float);
  15.     let sqrt_of_four = sqrtf(floored_float);
  17.     let sinus_of_four = sin(floored_float.into());
  19.     let exponential_of_four = exp(floored_float.into());
  20.     hprintln!("Floored test float {} to {}", float, floored_float).unwrap();
  21.     hprintln!("The square root of {} is {}", floored_float, sqrt_of_four).unwrap();
  22.     hprintln!("The sinus of four is {}", sinus_of_four).unwrap();
  23.     hprintln!(
  24.         "The exponential of four to the base e is {}",
  25.         exponential_of_four
  26.     )
  27.     .unwrap();
  28.     // exit QEMU
  29.     // NOTE do not run this on hardware; it can corrupt OpenOCD state
  30.     // debug::exit(debug::EXIT_SUCCESS);
  32.     loop {}
  33. }

If you need to perform more complex operations like DSP signal processing or advanced linear algebra on your MCU, the following crates might help you