Merge #308

308: added math chapter r=eldruin a=robamu

See #306 . I tried to gather some more information about available crates if more complex functionality is required and added links to them as well.

Co-authored-by: Robin Mueller <robin.mueller.m@gmail.com>

src/SUMMARY.md

@@ -53,6 +53,7 @@ more information and coordination
     - [A little Rust with your C](./interoperability/rust-with-c.md)
 - [Unsorted topics](./unsorted/index.md)
   - [Optimizations: The speed size tradeoff](./unsorted/speed-vs-size.md)
+  - [Performing Math Functionality](./unsorted/math.md)
 
 ---
 

src/unsorted/math.md

@@ -0,0 +1,75 @@
+# 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:
+
+```rs
+//! Some mathematical functions with standard support available
+
+fn main() {
+    let float: f32 = 4.82832;
+    let floored_float = float.floor();
+
+    let sqrt_of_four = floored_float.sqrt();
+
+    let sinus_of_four = floored_float.sin();
+
+    let exponential_of_four = floored_float.exp();
+    println!("Floored test float {} to {}", float, floored_float);
+    println!("The square root of {} is {}", floored_float, sqrt_of_four);
+    println!("The sinus of four is {}", sinus_of_four);
+    println!(
+        "The exponential of four to the base e is {}",
+        exponential_of_four
+    )
+}
+```
+
+Without standard library support, these functions are not available.
+An external crate like [`libm`](https://crates.io/crates/libm) can be used instead. The example code
+would then look like this:
+
+```rs
+#![no_main]
+#![no_std]
+
+use panic_halt as _;
+
+use cortex_m_rt::entry;
+use cortex_m_semihosting::{debug, hprintln};
+use libm::{exp, floorf, sin, sqrtf};
+
+#[entry]
+fn main() -> ! {
+    let float = 4.82832;
+    let floored_float = floorf(float);
+
+    let sqrt_of_four = sqrtf(floored_float);
+
+    let sinus_of_four = sin(floored_float.into());
+
+    let exponential_of_four = exp(floored_float.into());
+    hprintln!("Floored test float {} to {}", float, floored_float).unwrap();
+    hprintln!("The square root of {} is {}", floored_float, sqrt_of_four).unwrap();
+    hprintln!("The sinus of four is {}", sinus_of_four).unwrap();
+    hprintln!(
+        "The exponential of four to the base e is {}",
+        exponential_of_four
+    )
+    .unwrap();
+    // exit QEMU
+    // NOTE do not run this on hardware; it can corrupt OpenOCD state
+    // debug::exit(debug::EXIT_SUCCESS);
+
+    loop {}
+}
+```
+
+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
+
+- [CMSIS DSP library binding](https://github.com/jacobrosenthal/cmsis-dsp-sys)
+- [`micromath`](https://github.com/tarcieri/micromath)
+- [`microfft`](https://crates.io/crates/microfft)
+- [`nalgebra`](https://github.com/dimforge/nalgebra)