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| author | Adam Carpenter <gitlab@53hor.net> | 2019-07-09 15:14:04 -0400 |
|---|---|---|
| committer | Adam Carpenter <gitlab@53hor.net> | 2019-07-09 15:14:04 -0400 |
| commit | 7e8ee5ed9cad6484e9f13f81731b102ced58402e (patch) | |
| tree | 5395402ab07bbb5a659dbd68c701e22a1227202f /meap/meap-code/ch5/ch5-q/src | |
| download | learning-rust-7e8ee5ed9cad6484e9f13f81731b102ced58402e.tar.xz learning-rust-7e8ee5ed9cad6484e9f13f81731b102ced58402e.zip | |
Init.
Diffstat (limited to 'meap/meap-code/ch5/ch5-q/src')
| -rwxr-xr-x | meap/meap-code/ch5/ch5-q/src/lib.rs | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/meap/meap-code/ch5/ch5-q/src/lib.rs b/meap/meap-code/ch5/ch5-q/src/lib.rs new file mode 100755 index 0000000..d05ca3a --- /dev/null +++ b/meap/meap-code/ch5/ch5-q/src/lib.rs @@ -0,0 +1,76 @@ +/// Q1_7 - single byte representation of a fixed point number with range [-1, 1].
+/// The name refers to the Texas Instrument representation
+///
+/// References:
+/// - English Wikipedia: "Q (number format)" https://en.wikipedia.org/wiki/Q_(number_format)
+#[derive(Debug,Clone,Copy,PartialEq,Eq)]
+pub struct Q7(i8); // tuple struct holding a i8 value
+
+impl From<f64> for Q7 {
+ fn from (n: f64) -> Self {
+ if n >= 1.0 { // out of bounds numbers are coerced to the maximum of the range
+ Q7(127)
+ } else if n <= -1.0 {
+ Q7(-128)
+ } else {
+ Q7((n * 128.0) as i8) // 128 == (2 ** 7) == pow(2,7)
+ }
+ }
+}
+
+impl From<Q7> for f64 {
+ fn from(n: Q7) -> f64 {
+ (n.0 as f64) * 2f64.powf(-7.0) // 0.0078125// (2 ** -7) // pow(2, -7)
+ }
+}
+
+impl From<f32> for Q7 {
+ fn from (n: f32) -> Self {
+ Q7::from(n as f64) // conversion from f32 to f64 works perfectly
+ }
+}
+
+impl From<Q7> for f32 {
+ fn from(n: Q7) -> f32 {
+ f64::from(n) as f32 // conversion from f64 to f32 can result in undefined behavior,
+ // but not here as f32 can represent all values representable by Q7
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn out_of_bounds() {
+ assert_eq!(Q7::from(10.), Q7::from(1.));
+ assert_eq!(Q7::from(-10.), Q7::from(-1.));
+ }
+
+ #[test]
+ fn f32_to_q7() {
+ let n1: f32 = 0.7;
+ let q1 = Q7::from(n1);
+
+ let n2 = -0.4;
+ let q2 = Q7::from(n2);
+
+ let n3 = 123.0;
+ let q3 = Q7::from(n3);
+
+ assert_eq!(q1, Q7(89));
+ assert_eq!(q2, Q7(-51));
+ assert_eq!(q3, Q7(127));
+ }
+
+ #[test]
+ fn q7_to_f32() {
+ let q1 = Q7::from(0.7);
+ let n1 = f32::from(q1);
+ assert_eq!(n1, 0.6953125);
+
+ let q2 = Q7::from(n1); // numbers that can be represented exactly by Q7
+ let n2 = f32::from(q2); // can survive the transition between Q7 and f32
+ assert_eq!(n1, n2);
+ }
+}
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