Split transform into forward and inverse

src/lib.rs

@@ -1,25 +1,23 @@
 #![feature(step_by)]
 
-/// A direction of the Fourier transform.
-pub enum Direction {
-    /// From the time domain to the frequency domain.
-    Forward,
-    /// From the frequency domain to the time domain.
-    Inverse,
+/// Perform the Fourier transform.
+#[inline(always)]
+pub fn forward(data: &mut [f64]) {
+    transform(data, 1.0);
 }
 
-/// Perform the Fourier transform.
-pub fn transform(data: &mut [f64], direction: Direction) {
+/// Perform the inverse Fourier transform.
+#[inline(always)]
+pub fn inverse(data: &mut [f64]) {
+    transform(data, -1.0);
+}
+
+fn transform(data: &mut [f64], isign: f64) {
     use std::f64::consts::PI;
 
     let n = data.len() / 2;
     let nn = n << 1;
 
-    let isign = match direction {
-        Direction::Forward => 1.0,
-        Direction::Inverse => -1.0,
-    };
-
     let mut j = 1;
     for i in (1..nn).step_by(2) {
         if j > i {
@@ -60,7 +58,7 @@ pub fn transform(data: &mut [f64], direction: Direction) {
         mmax = istep;
     }
 
-    if let Direction::Inverse = direction {
+    if isign == -1.0 {
         let scale = 1.0 / n as f64;
         for i in 0..(2 * n) {
             data[i] *= scale;

tests/lib.rs

@@ -4,15 +4,15 @@ extern crate fft;
 mod fixtures;
 
 #[test]
-fn transform_forward() {
+fn forward() {
     let mut data = fixtures::TIME_DATA.to_vec();
-    fft::transform(&mut data, fft::Direction::Forward);
+    fft::forward(&mut data);
     assert::close(&data, &fixtures::FREQUENCY_DATA[..], 1e-13);
 }
 
 #[test]
-fn transform_inverse() {
+fn inverse() {
     let mut data = fixtures::FREQUENCY_DATA.to_vec();
-    fft::transform(&mut data, fft::Direction::Inverse);
+    fft::inverse(&mut data);
     assert::close(&data, &fixtures::TIME_DATA[..], 1e-13);
 }