use arrays instead of vectors

which makes the li2() and li3() functions ~ 7% faster.

src/li2.rs

@@ -24,7 +24,7 @@ impl Li2<f64> for f64 {
         let pi2 = pi*pi;
         let pi3 = pi2/3.;
         let pi6 = pi2/6.;
-        let coeffs = vec![0.42996693560813697, 0.40975987533077105,
+        let coeffs = [0.42996693560813697, 0.40975987533077105,
            -0.01858843665014592, 0.00145751084062268,-0.00014304184442340,
             0.00001588415541880,-0.00000190784959387, 0.00000024195180854,
            -0.00000003193341274, 0.00000000434545063,-0.00000000060578480,
@@ -97,7 +97,7 @@ impl Li2<Complex<f64>> for Complex<f64> {
 
         // bf[1..N-1] are the even Bernoulli numbers / (2 n + 1)!
         // generated by: Table[BernoulliB[2 n]/(2 n + 1)!, {n, 1, 19}]
-        let bf = vec![
+        let bf = [
             - 1./4.,
               1./36.,
             - 1./36.0e2,

src/li3.rs

@@ -28,7 +28,7 @@ impl Li3<Complex<f64>> for Complex<f64> {
         let pi2 = pi*pi;
         let eps = std::f64::EPSILON;
         let z3  = 1.2020569031595942853997381615114;
-        let bf  = vec![
+        let bf  = [
             1., -3./8., 17./216., -5./576.,
              0.00012962962962962962962962962962963,  0.000081018518518518518518518518518519,
             -3.4193571608537594932152755282007e-06, -1.3286564625850340136054421768707e-06 ,
@@ -90,7 +90,7 @@ impl Li3<Complex<f64>> for Complex<f64> {
 
         let mut p = Complex::new(1.,0.);
 
-        for b in bf {
+        for b in bf.iter() {
             p *= u;
             sum += b*p;
         }

tests/li2.rs

@@ -138,7 +138,7 @@ fn identities() {
     let eps = 1e-14;
     let zero = Complex::zero();
     let omega = Complex::new(0.5, (3.).sqrt()/2.);
-    let values = vec![
+    let values = [
         Complex::new(0.,0.),
         Complex::new(0.5,0.),
         Complex::new(1.,0.),