package blas

// Compute the sum Y = \alpha X + Y for the vectors X and Y 
func Daxpy(N int, alpha float64, X []float64, incX int, Y []float64, incY int)

func daxpy(N int, alpha float64, X []float64, incX int, Y []float64, incY int) {
	var xi, yi int
	switch alpha {
	case 0:
	case 1:
		for ; N >= 2; N -= 2 {
			Y[yi] += X[xi]
			xi += incX
			yi += incY

			Y[yi] += X[xi]
			xi += incX
			yi += incY
		}
		if N != 0 {
			Y[yi] += alpha * X[xi]
		}
	case -1:
		for ; N >= 2; N -= 2 {
			Y[yi] -= X[xi]
			xi += incX
			yi += incY

			Y[yi] -= X[xi]
			xi += incX
			yi += incY
		}
		if N != 0 {
			Y[yi] -= X[xi]
		}
	default:
		for ; N >= 2; N -= 2 {
			Y[yi] += alpha * X[xi]
			xi += incX
			yi += incY

			Y[yi] += alpha * X[xi]
			xi += incX
			yi += incY
		}
		if N != 0 {
			Y[yi] += alpha * X[xi]
		}
	}
}