diff --git a/src/complex.rs b/src/complex.rs
new file mode 100644
index 0000000..1e07b21
--- /dev/null
+++ b/src/complex.rs
@@ -0,0 +1,42 @@
+use std::ops::{Add, Mul, Sub};
+
+/// A complex number.
+#[allow(non_camel_case_types)]
+#[derive(Clone, Copy, Debug)]
+pub struct c64(pub f64, pub f64);
+
+impl Add for c64 {
+    type Output = Self;
+
+    #[inline(always)]
+    fn add(self, rhs: c64) -> c64 {
+        c64(self.0 + rhs.0, self.1 + rhs.1)
+    }
+}
+
+impl Mul for c64 {
+    type Output = Self;
+
+    #[inline(always)]
+    fn mul(self, rhs: c64) -> c64 {
+        c64(self.0 * rhs.0 - self.1 * rhs.1, self.0 * rhs.1 + self.1 * rhs.0)
+    }
+}
+
+impl Mul<f64> for c64 {
+    type Output = Self;
+
+    #[inline(always)]
+    fn mul(self, rhs: f64) -> c64 {
+        c64(self.0 * rhs, self.1 * rhs)
+    }
+}
+
+impl Sub for c64 {
+    type Output = Self;
+
+    #[inline(always)]
+    fn sub(self, rhs: c64) -> c64 {
+        c64(self.0 - rhs.0, self.1 - rhs.1)
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 6334796..7f57964 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,96 +1,139 @@
-#![feature(step_by)]
+use std::slice;
+
+mod complex;
+pub use complex::c64;
+
+/// A means of obtaining a slice of mutable complex numbers.
+pub trait AsMutComplex<'l> {
+    fn as_mut_complex(self) -> &'l mut [c64];
+}
+
+impl<'l> AsMutComplex<'l> for &'l mut [c64] {
+    #[inline(always)]
+    fn as_mut_complex(self) -> &'l mut [c64] {
+        self
+    }
+}
+
+impl<'l> AsMutComplex<'l> for &'l mut [f64] {
+    /// Treat the slice as a collection of pairs of real and imaginary parts and
+    /// reinterpret it as a slice of complex numbers.
+    ///
+    /// ## Panics
+    ///
+    /// The function panics if the number of elements is not even.
+    #[inline]
+    fn as_mut_complex(self) -> &'l mut [c64] {
+        unsafe {
+            let length = self.len();
+            assert!(length % 2 == 0, "the number of elements should be even");
+            slice::from_raw_parts_mut(self.as_mut_ptr() as *mut _, length / 2)
+        }
+    }
+}
+
+impl<'l> AsMutComplex<'l> for &'l mut Vec<f64> {
+    #[inline]
+    fn as_mut_complex(self) -> &'l mut [c64] {
+        <&mut [f64]>::as_mut_complex(&mut *self)
+    }
+}
 
 /// Perform the Fourier transform.
 ///
-/// `data` should contain `n` complex numbers where `n` is a power of two. Each
-/// complex number is stored as a pair of `f64`s so that the first is the real
-/// part and the second is the corresponding imaginary part. Hence, the total
-/// length of `data` should be `2 × n`.
-///
-/// # Panics
-///
-/// The function panics if `data.len()` is not even or `data.len() / 2` is not a
-/// power of two.
+/// The number of points should be a power of two.
 #[inline(always)]
-pub fn forward(data: &mut [f64]) {
-    transform(data, 1.0);
+pub fn forward<'l, T: AsMutComplex<'l>>(data: T) {
+    let data = data.as_mut_complex();
+
+    let n = data.len();
+    if n < 1 || n & (n - 1) != 0 {
+        panic!("expected the number of points to be a power of two");
+    }
+
+    rearrange(data, n);
+    perform(data, n, false);
 }
 
 /// Perform the inverse Fourier transform.
 ///
-/// `data` should contain `n` complex numbers where `n` is a power of two. Each
-/// complex number is stored as a pair of `f64`s so that the first is the real
-/// part and the second is the corresponding imaginary part. Hence, the total
-/// length of `data` should be `2 × n`.
-///
-/// # Panics
-///
-/// The function panics if `data.len()` is not even or `data.len() / 2` is not a
-/// power of two.
+/// The number of points should be a power of two.
 #[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 l = data.len();
-    if l % 2 != 0 {
-        panic!("expected the length of the data to be even");
-    }
+pub fn inverse<'l, T: AsMutComplex<'l>>(data: T, scaling: bool) {
+    let data = data.as_mut_complex();
 
-    let n = l / 2;
+    let n = data.len();
     if n < 1 || n & (n - 1) != 0 {
         panic!("expected the number of points to be a power of two");
     }
 
-    let nn = n << 1;
+    rearrange(data, n);
+    perform(data, n, true);
+    if scaling {
+        scale(data, n);
+    }
+}
 
-    let mut j = 1;
-    for i in (1..nn).step_by(2) {
-        if j > i {
-            data.swap(j - 1, i - 1);
-            data.swap(j, i);
+#[inline(always)]
+fn rearrange(data: &mut [c64], n: usize) {
+    let mut target = 0;
+    for position in 0..n {
+        if target > position {
+            data.swap(position, target);
         }
-        let mut m = n;
-        while m >= 2 && j > m {
-            j -= m;
-            m >>= 1;
+        let mut mask = n >> 1;
+        while target & mask != 0 {
+            target &= !mask;
+            mask >>= 1;
         }
-        j += m;
+        target |= mask;
     }
+}
 
-    let mut mmax = 2;
-    while nn > mmax {
-        let istep = mmax << 1;
-        let theta = isign * (2.0 * PI / mmax as f64);
-        let wtemp = (0.5 * theta).sin();
-        let wpr = -2.0 * wtemp * wtemp;
-        let wpi = theta.sin();
-        let mut wr = 1.0;
-        let mut wi = 0.0;
-        for m in (1..mmax).step_by(2) {
-            for i in (m..(nn + 1)).step_by(istep) {
-                let j = i + mmax;
-                let tempr = wr * data[j - 1] - wi * data[j];
-                let tempi = wr * data[j] + wi * data[j - 1];
-                data[j - 1] = data[i - 1] - tempr;
-                data[j] = data[i] - tempi;
-                data[i - 1] += tempr;
-                data[i] += tempi;
+#[inline(always)]
+fn perform(data: &mut [c64], n: usize, inverse: bool) {
+    use std::f64::consts::PI;
+
+    let pi = if inverse { PI } else { -PI };
+
+    let mut step = 1;
+    while step < n {
+        let jump = step << 1;
+        let delta = pi / step as f64;
+        let sine = (0.5 * delta).sin();
+        let multiplier = c64(-2.0 * sine * sine, delta.sin());
+        let mut factor = c64(1.0, 0.0);
+        for group in 0..step {
+            let mut pair = group;
+            while pair < n {
+                let match_pair = pair + step;
+                let product = factor * data[match_pair];
+                data[match_pair] = data[pair] - product;
+                data[pair] = data[pair] + product;
+                pair += jump;
             }
-            let wtemp = wr;
-            wr = wr * wpr - wi * wpi + wr;
-            wi = wi * wpr + wtemp * wpi + wi;
+            factor = multiplier * factor + factor;
         }
-        mmax = istep;
+        step <<= 1;
     }
+}
 
-    if isign == -1.0 {
-        let scale = 1.0 / n as f64;
-        for i in 0..l {
-            data[i] *= scale;
-        }
+#[inline(always)]
+fn scale(data: &mut [c64], n: usize) {
+    let factor = 1.0 / n as f64;
+    for position in 0..n {
+        data[position] = data[position] * factor;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use c64;
+    use std::mem;
+
+    #[test]
+    fn size_of() {
+        assert_eq!(mem::size_of::<c64>(), 2 * mem::size_of::<f64>());
+        assert_eq!(mem::size_of::<[c64; 42]>(), 2 * mem::size_of::<[f64; 42]>());
     }
 }
diff --git a/tests/fixtures.rs b/tests/fixtures.rs
index 43a464a..cc8793a 100644
--- a/tests/fixtures.rs
+++ b/tests/fixtures.rs
@@ -130,132 +130,132 @@ pub const TIME_DATA: [f64; 256] = [
 ];
 
 pub const FREQUENCY_DATA: [f64; 256] = [
-    67.506562667203411, 62.798747687506840,
-    -2.916435892389177,  2.258137395096745,
-    -1.213411748796466, -2.824305441697990,
-    -3.884636396852776, -6.613971933163763,
-     5.049316157478026,  0.456883084114653,
-    -0.466361441955149, -5.481824322589378,
-     0.803910676769211,  0.147054274059631,
-    -6.749332581521054,  4.840407656923564,
-    -0.262756329494097,  3.254410744830774,
-    -6.973431206318843,  1.575164194822261,
-    -5.636666719031166, -3.624154259337717,
-    -1.286794839414061, -3.596629452384591,
-    -1.949442402686498, -1.250892366300883,
-    -2.956509867164284, -3.563268353779529,
-    -1.629751417352084,  4.497170521285449,
-     1.320095075374985, -2.156073489574812,
-    -2.002497059929997, -3.607915605047517,
-     2.554697843376545, -2.629716248632329,
-     2.398999344465010, -0.074112453018754,
-     1.495969367959889,  1.905315704750475,
-    -2.236600417683027,  0.738926830782050,
-    -0.048604481554162, -2.372949299902079,
-     3.012458946272938, -6.457540983540477,
-    -0.751768100557872,  2.124100304630884,
-    -1.792775263985138,  0.264154836959835,
-    -0.307176194080528, -5.087687483603743,
-    -1.005151880556302,  2.902422614798144,
-     0.724987856799877, -2.068196780758698,
-    -0.342018034885117,  2.522012423589103,
-    -0.434808099354017,  2.147158479497558,
-    -2.674474141084141, -2.563372692380105,
-    -6.632075418392929, -1.685124294109070,
-    -2.699185197567189, -5.897826029871508,
-    -0.241335159541328,  3.101405290332420,
-     2.979104548159058, -1.160028660033103,
-     4.840508528923102, -3.204368559739159,
-    -3.399157829092539,  2.161358937350348,
-     4.878539287722978, -1.459376706664861,
-    -0.426496319168839,  3.030254700260016,
-     5.146915245537944,  0.282061559224328,
-    -0.008414044119338, -3.991754204800235,
-     3.638877999600389,  1.258926814764483,
-     1.909130437842078,  0.995539872732337,
-     6.414605960628886, -5.679739832207080,
-     3.905872946117078, -2.826501461749101,
-     0.967386492473095, -5.576552424605286,
-    -2.853890281653033, -3.715099310600197,
-    -0.998730499887771, -1.368332585830762,
-     0.539665253171003,  0.702327760413163,
-    -2.202133267022090,  1.329217526808806,
-     0.923776499928182,  2.150735454872208,
-     2.473335187775022, -0.373719659978438,
-    -2.253868990511847, -2.913770876062729,
-    -0.368246167526135, -1.498059975229275,
-    -0.075789241425793,  1.719766675858378,
-    -6.249259838595410,  6.001167756824215,
-    -4.027346047616200,  5.509694798065765,
-    -3.923350081315725, -0.896137928694981,
-    -0.923595644189471, -1.735427210626094,
-    -3.429327683732347,  0.363408609675781,
-    -2.276214983007463, -0.860532742279556,
-     2.965000493451818,  5.042549679265357,
-     2.949752700932401,  2.757985604650260,
-    -7.551126038911468, -1.253320876553430,
-    -3.991693675979835, -2.395612192990079,
-    -3.231893261005089, -3.499165263231712,
-    -1.385547239860866,  4.278296734710755,
-    -2.521465228517418, -1.483012583302978,
-     2.166953458666462,  3.698992188846230,
-    -1.718586561803937, -2.848378813769423,
-     2.356251252889540,  3.100152502890587,
-    -1.680667450021412, -5.672119730229592,
-     3.266763808523838, -4.939142356746459,
-    -0.677140885336755,  7.689403378304775,
-     0.714397029389201, -1.027012942409025,
-     4.548911919541158, -3.110338786263284,
-     0.963824257168846, -1.315676780411989,
-    -0.630783224843193, -1.040038800556799,
-     0.051441799174254,  8.187374675121179,
-     2.897552781182147,  4.424347873913396,
-     3.813912169625594,  1.672124644400444,
-    -1.849780677085411, -6.075332676660434,
-    -3.451402723746721, -0.201945959802337,
-    -2.768891360840025,  1.367687274872978,
-    -1.559401743047184, -2.563598701770972,
-    -1.874383165372955, -1.816379942063397,
-     4.841738890983525,  4.304535776881384,
-    -1.617862103749635,  4.505029568623651,
-     3.144799926493496,  0.532041249412581,
-    -3.772195284223951,  2.554683615488583,
-     1.466063738740647,  0.328554468964208,
-     2.211012545853337, -3.584550392170861,
-    -5.848019862181538, -1.853688693742572,
-    -1.310659972997355, -4.744849190522960,
-     2.553617632271563, -2.515247887047404,
-     4.482138368790012, -8.618372361868635,
-     0.884305207470568,  1.209832476084043,
-     0.983852564385845, -1.970780039723666,
-    -4.755886984684762, -2.371006165743844,
-    -2.386952673947499, -0.380046032794893,
-     8.202058412989162, -1.912136722291743,
-     1.303130356713501,  0.110408680312637,
-     4.396893371992936, -1.781029123711262,
-    -5.653027779602041, -4.457764259327377,
-     2.344622479665089,  0.978245756031540,
-     0.085165407317421,  1.846582481253430,
-     2.305750958010686,  0.037116571959843,
-     2.090636515202623, -2.544058986903603,
-    -1.098781173708802, -4.976387399730235,
-     3.116401263119525,  0.806086033998370,
-    -7.921745368568139, -7.472969089954924,
-     1.411453345272358, -1.449094611132407,
-    -0.804853562658514,  4.667294297528407,
-     4.288737227223235, -3.968319162458097,
-    -2.972572998085656,  5.831133886072563,
-     0.840509623087476,  4.498605610210712,
-     2.983076467939862, -3.013246639835036,
-     3.880468387697881,  1.634838899334426,
-    -4.944656692463916,  5.315462183419951,
-     4.133604334208203, -3.445364011535503,
-    -3.599237215989622, -1.105183198676706,
-    -3.458371226842255,  8.013344593032475,
-    -5.278077778941197, -4.066322943629892,
-     0.772765865031132, -8.707366039824819,
-    -0.108445528881629, -0.965343418118287,
-     4.308501796277244, -0.278006225941031,
-    -5.303978155417413, -0.288754984960703,
-     0.077148388378536,  5.819389938527753,
+     6.750656266720340e+01,  6.279874768750683e+01,
+     7.714838837855442e-02,  5.819389938527752e+00,
+    -5.303978155417409e+00, -2.887549849606836e-01,
+     4.308501796277235e+00, -2.780062259410463e-01,
+    -1.084455288816293e-01, -9.653434181182980e-01,
+     7.727658650311002e-01, -8.707366039824819e+00,
+    -5.278077778941212e+00, -4.066322943629877e+00,
+    -3.458371226842232e+00,  8.013344593032468e+00,
+    -3.599237215989637e+00, -1.105183198676696e+00,
+     4.133604334208186e+00, -3.445364011535524e+00,
+    -4.944656692463901e+00,  5.315462183419959e+00,
+     3.880468387697888e+00,  1.634838899334416e+00,
+     2.983076467939860e+00, -3.013246639835038e+00,
+     8.405096230874929e-01,  4.498605610210712e+00,
+    -2.972572998085648e+00,  5.831133886072569e+00,
+     4.288737227223233e+00, -3.968319162458111e+00,
+    -8.048535626585105e-01,  4.667294297528397e+00,
+     1.411453345272351e+00, -1.449094611132408e+00,
+    -7.921745368568175e+00, -7.472969089954909e+00,
+     3.116401263119543e+00,  8.060860339983653e-01,
+    -1.098781173708808e+00, -4.976387399730230e+00,
+     2.090636515202629e+00, -2.544058986903604e+00,
+     2.305750958010683e+00,  3.711657195983209e-02,
+     8.516540731741751e-02,  1.846582481253431e+00,
+     2.344622479665092e+00,  9.782457560315421e-01,
+    -5.653027779602048e+00, -4.457764259327358e+00,
+     4.396893371992927e+00, -1.781029123711273e+00,
+     1.303130356713504e+00,  1.104086803126383e-01,
+     8.202058412989162e+00, -1.912136722291750e+00,
+    -2.386952673947501e+00, -3.800460327948856e-01,
+    -4.755886984684770e+00, -2.371006165743835e+00,
+     9.838525643858385e-01, -1.970780039723673e+00,
+     8.843052074705682e-01,  1.209832476084040e+00,
+     4.482138368789980e+00, -8.618372361868662e+00,
+     2.553617632271545e+00, -2.515247887047421e+00,
+    -1.310659972997361e+00, -4.744849190522960e+00,
+    -5.848019862181545e+00, -1.853688693742562e+00,
+     2.211012545853336e+00, -3.584550392170881e+00,
+     1.466063738740644e+00,  3.285544689641922e-01,
+    -3.772195284223943e+00,  2.554683615488591e+00,
+     3.144799926493497e+00,  5.320412494125712e-01,
+    -1.617862103749616e+00,  4.505029568623644e+00,
+     4.841738890983537e+00,  4.304535776881372e+00,
+    -1.874383165372953e+00, -1.816379942063393e+00,
+    -1.559401743047192e+00, -2.563598701770973e+00,
+    -2.768891360840021e+00,  1.367687274872984e+00,
+    -3.451402723746730e+00, -2.019459598023322e-01,
+    -1.849780677085415e+00, -6.075332676660432e+00,
+     3.813912169625591e+00,  1.672124644400447e+00,
+     2.897552781182169e+00,  4.424347873913383e+00,
+     5.144179917427660e-02,  8.187374675121173e+00,
+    -6.307832248431945e-01, -1.040038800556793e+00,
+     9.638242571688409e-01, -1.315676780411990e+00,
+     4.548911919541162e+00, -3.110338786263292e+00,
+     7.143970293892079e-01, -1.027012942409028e+00,
+    -6.771408853367402e-01,  7.689403378304775e+00,
+     3.266763808523832e+00, -4.939142356746464e+00,
+    -1.680667450021413e+00, -5.672119730229586e+00,
+     2.356251252889546e+00,  3.100152502890580e+00,
+    -1.718586561803939e+00, -2.848378813769422e+00,
+     2.166953458666474e+00,  3.698992188846235e+00,
+    -2.521465228517406e+00, -1.483012583302976e+00,
+    -1.385547239860872e+00,  4.278296734710759e+00,
+    -3.231893261005089e+00, -3.499165263231714e+00,
+    -3.991693675979821e+00, -2.395612192990072e+00,
+    -7.551126038911470e+00, -1.253320876553413e+00,
+     2.949752700932412e+00,  2.757985604650246e+00,
+     2.965000493451835e+00,  5.042549679265349e+00,
+    -2.276214983007470e+00, -8.605327422795508e-01,
+    -3.429327683732336e+00,  3.634086096757940e-01,
+    -9.235956441894744e-01, -1.735427210626094e+00,
+    -3.923350081315737e+00, -8.961379286949720e-01,
+    -4.027346047616183e+00,  5.509694798065775e+00,
+    -6.249259838595390e+00,  6.001167756824247e+00,
+    -7.578924142578991e-02,  1.719766675858380e+00,
+    -3.682461675261361e-01, -1.498059975229270e+00,
+    -2.253868990511852e+00, -2.913770876062722e+00,
+     2.473335187775014e+00, -3.737196599784345e-01,
+     9.237764999281854e-01,  2.150735454872202e+00,
+    -2.202133267022083e+00,  1.329217526808811e+00,
+     5.396652531710098e-01,  7.023277604131626e-01,
+    -9.987304998877746e-01, -1.368332585830754e+00,
+    -2.853890281653036e+00, -3.715099310600182e+00,
+     9.673864924730763e-01, -5.576552424605284e+00,
+     3.905872946117088e+00, -2.826501461749119e+00,
+     6.414605960628869e+00, -5.679739832207091e+00,
+     1.909130437842080e+00,  9.955398727323348e-01,
+     3.638877999600390e+00,  1.258926814764474e+00,
+    -8.414044119346986e-03, -3.991754204800230e+00,
+     5.146915245537949e+00,  2.820615592243083e-01,
+    -4.264963191688312e-01,  3.030254700260019e+00,
+     4.878539287722978e+00, -1.459376706664878e+00,
+    -3.399157829092533e+00,  2.161358937350359e+00,
+     4.840508528923103e+00, -3.204368559739170e+00,
+     2.979104548159062e+00, -1.160028660033101e+00,
+    -2.413351595413149e-01,  3.101405290332420e+00,
+    -2.699185197567189e+00, -5.897826029871508e+00,
+    -6.632075418392930e+00, -1.685124294109047e+00,
+    -2.674474141084143e+00, -2.563372692380101e+00,
+    -4.348080993540033e-01,  2.147158479497566e+00,
+    -3.420180348851098e-01,  2.522012423589093e+00,
+     7.249878567998773e-01, -2.068196780758695e+00,
+    -1.005151880556292e+00,  2.902422614798151e+00,
+    -3.071761940805398e-01, -5.087687483603752e+00,
+    -1.792775263985136e+00,  2.641548369598412e-01,
+    -7.517681005578722e-01,  2.124100304630884e+00,
+     3.012458946272915e+00, -6.457540983540484e+00,
+    -4.860448155416430e-02, -2.372949299902082e+00,
+    -2.236600417683022e+00,  7.389268307820533e-01,
+     1.495969367959897e+00,  1.905315704750479e+00,
+     2.398999344465012e+00, -7.411245301876057e-02,
+     2.554697843376545e+00, -2.629716248632333e+00,
+    -2.002497059929998e+00, -3.607915605047513e+00,
+     1.320095075374978e+00, -2.156073489574819e+00,
+    -1.629751417352065e+00,  4.497170521285455e+00,
+    -2.956509867164297e+00, -3.563268353779526e+00,
+    -1.949442402686502e+00, -1.250892366300881e+00,
+    -1.286794839414063e+00, -3.596629452384589e+00,
+    -5.636666719031170e+00, -3.624154259337708e+00,
+    -6.973431206318839e+00,  1.575164194822264e+00,
+    -2.627563294940978e-01,  3.254410744830774e+00,
+    -6.749332581521038e+00,  4.840407656923577e+00,
+     8.039106767692121e-01,  1.470542740596267e-01,
+    -4.663614419551561e-01, -5.481824322589377e+00,
+     5.049316157478017e+00,  4.568830841146547e-01,
+    -3.884636396852787e+00, -6.613971933163752e+00,
+    -1.213411748796469e+00, -2.824305441697994e+00,
+    -2.916435892389174e+00,  2.258137395096740e+00,
 ];
diff --git a/tests/lib.rs b/tests/lib.rs
index 453e8c1..1aa55e3 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -13,6 +13,6 @@ fn forward() {
 #[test]
 fn inverse() {
     let mut data = fixtures::FREQUENCY_DATA.to_vec();
-    fft::inverse(&mut data);
+    fft::inverse(&mut data, true);
     assert::close(&data, &fixtures::TIME_DATA[..], 1e-13);
 }