Vector dot product: BLAS accelerated implementation + naive implementation

dot.rs

use std::iter::AdditiveIterator;
use std::num::Zero;

#[link(name = "blas")]
extern {
    fn ddot_(N: *int, x: *f64, inc_x: *int, y: *f64, inc_y: *int) -> f64;
    fn sdot_(N: *int, x: *f32, inc_x: *int, y: *f32, inc_y: *int) -> f32;
}

trait VectorDot<T> {
    fn dot(&self, rhs: &Vec<T>) -> T;
}

// FIXME how to tell the compiler to use the BLAS accelerated implementations
// for f32 and f64, but use this fallback implementation for the rest of cases
impl<
    T: Add<T, T> + Mul<T, T> + Zero
> VectorDot<T>
for Vec<T> {
    fn dot(&self, rhs: &Vec<T>) -> T {
        assert!(self.len() == rhs.len(), "dimension mismatch");

        self.as_slice().iter().zip(rhs.as_slice().iter()).map(|(x, y)| x.mul(y)).sum()
    }
}

// Error: conflicting implementations for trait VectorDot
//impl
//VectorDot<f32>
//for Vec<f32> {
    //fn dot(&self, rhs: &Vec<f32>) -> f32 {
        //assert!(self.len() == rhs.len(), "dimension mismatch");

        //unsafe {
            //sdot_(&(self.len() as int) as *_,
                  //self.as_ptr(),
                  //&1 as *_,
                  //rhs.as_ptr(),
                  //&1 as *_)
        //}
    //}
//}

// Error: conflicting implementations for trait VectorDot
//impl
//VectorDot<f64>
//for Vec<f64> {
    //fn dot(&self, rhs: &Vec<f64>) -> f64 {
        //assert!(self.len() == rhs.len(), "dimension mismatch");

        //unsafe {
            //ddot_(&(self.len() as int) as *_,
                  //self.as_ptr(),
                  //&1 as *_,
                  //rhs.as_ptr(),
                  //&1 as *_)
        //}
    //}
//}

fn main() {
    let x: Vec<f64> = vec!(1.0, 2.0, 3.0);
    let y: Vec<f64> = vec!(3.0, 2.0, 1.0);

    // BLAS
    assert_eq!(x.dot(&y), 10.0);

    let x: Vec<f32> = vec!(1.0, 2.0, 3.0);
    let y: Vec<f32> = vec!(3.0, 2.0, 1.0);

    // BLAS
    assert_eq!(x.dot(&y), 10.0);

    let x = vec!(1, 2, 3);
    let y = vec!(3, 2, 1);

    // fallback
    assert_eq!(x.dot(&y), 10);
}