Init.

3 files changed, 210 insertions, 0 deletions

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new file mode 100755
index 0000000..3ac932f
--- /dev/null
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diff --git a/meap/meap-code/ch5/ch5-q/Cargo.toml b/meap/meap-code/ch5/ch5-q/Cargo.toml
new file mode 100755
index 0000000..ffd0826
--- /dev/null
+++ b/meap/meap-code/ch5/ch5-q/Cargo.toml
@@ -0,0 +1,7 @@
+[package]

+name = "ch5-q"

+version = "0.1.0"

+authors = ["Tim McNamara <code@timmcnamara.co.nz>"]

+

+[dependencies]

+num = "*"
\ No newline at end of file
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);

+    }

+}