Rustify some code.

src/math.rs

@@ -88,41 +88,38 @@ fn p1evl(x: f64, coef: &[f64], n: usize) -> f64 {
 }
 
 fn ndtri(y0: f64) -> f64 {
-    let mut code = 1;
     let mut y = y0;
 
-    if y > (1.0 - 0.13533528323661269189) {
+    let code = if y > (1.0 - 0.13533528323661269189) {
         y = 1.0 - y;
-        code = 0;
-    }
+
+        false
+    } else {
+        true
+    };
 
     if y > 0.13533528323661269189 {
         y = y - 0.5;
         let y2 = y * y;
-        let x = y + y * (y2 * polevl(y2, &P0, 4) / p1evl(y2, &Q0, 8));
-        let x = x * S2PI;
 
-        return x;
+        return (y + y * (y2 * polevl(y2, &P0, 4) / p1evl(y2, &Q0, 8))) * S2PI;
     }
 
     let x = (-2.0 * y.ln()).sqrt();
-    let x0 = x - x.ln() / x;
-
     let z = 1.0 / x;
 
+    let x0 = x - x.ln() / x;
     let x1 = if x < 8.0 {
         z * polevl(z, &P1, 8) / p1evl(z, &Q1, 8)
     } else {
         z * polevl(z, &P2, 8) / p1evl(z, &Q2, 8)
     };
 
-    let mut x = x0 - x1;
-
-    if code != 0 {
-        x = -x;
+    if code {
+        x1 - x0
+    } else {
+        x0 - x1
     }
-
-    x
 }
 
 pub fn cdf(x: f64) -> f64 {