Fixed up nostd support, verified that sqrt and cbrt routines work to within 1ULP

firmware/jerk_control/src/executor.rs

@@ -36,7 +36,7 @@ impl CommandQueue {
     // Returns true if step signal should be high. This does the first, constant time part of stepping.
     // Note that step_late needs to be called as well to advance the segment.
     pub fn step_early(&mut self) -> bool {
-
+        
         let cur_segment = &mut self.segments[self.cur_segment as usize];
 
         self.p.0 = (self.p + cur_segment.delta[0]).0.rem_euclid(self.step_size);

firmware/jerk_control/src/lib.rs

@@ -1,4 +1,4 @@
-// #![no_std]
+#![no_std]
 
 pub mod planner;
 pub mod executor;

firmware/jerk_control/src/math_ext.rs

@@ -41,12 +41,22 @@ fn sqrt_approx(value: f32) -> f32 {
 pub fn cbrt_approx(value: f32) -> f32 {
     let value = value.to_bits();
 
-	const EXP_BIAS: i32 = 0x3f80_0000;
+	//const EXP_BIAS: i32 = 0x3f80_0000;
 
 	f32::from_bits((value & 0x8000_0000) |
-					   (((value as i32 & 0x7fff_ffff) - EXP_BIAS) / 3 + EXP_BIAS) as u32)
+					   (((value & 0x7fff_ffff) / 3).wrapping_add(0x2a5119f2)))
 }
 
+fn frexp(value: f32) -> (i32, f32) {
+    let value = value.to_bits();
+    (((value >> 23) & 0xff) as i32 - 126, // we go to [0.5,1), whereas the mantissa represents [1,2)
+     f32::from_bits(value & 0x7f_ffff | (126 << 23)))
+}
+fn ldexp(exp: i32, mantissa: f32) -> f32 {
+    f32::from_bits(mantissa.to_bits().wrapping_add((exp as u32) << 23))
+}
+
+
 impl Roots for f32 {
     fn sqrt(self) -> Self {
 	let mut estimate = sqrt_approx(self);
@@ -56,16 +66,18 @@ impl Roots for f32 {
 	estimate
     }
 
+    //#[cfg(ignore)]
     fn cbrt(self) -> Self {
-	let mut estimate = cbrt_approx(self); // TODO: improve this with bit twiddling
-
+	let mut estimate = cbrt_approx(self) as f64; // TODO: improve this with bit twiddling
+	let a = self as f64;
+	
 	// Use halley's method to refine the approximation.
-	for _ in 0..3 {
+	for _ in 0..2 {
 	    let e3 = estimate * estimate * estimate;
-	    estimate = estimate * (e3 + self + self) / ( e3 + e3 + self);
+	    estimate = estimate * (e3 + a + a) / ( e3 + e3 + a);
 	}
 	
-	estimate
+	estimate as f32
     }
 }
 

firmware/jerk_control/src/planner.rs

@@ -5,6 +5,7 @@
 
 use core::num::Wrapping;
 use core::option::Option;
+use crate::math_ext::Roots as _;
 
 pub struct Config {
     /// Max jerk, in mm/s^3