picomath

(define (erf x)
    ; constants
    (let* ((a1  0.254829592)
           (a2 -0.284496736)
           (a3  1.421413741)
           (a4 -1.453152027)
           (a5  1.061405429)
           (p   0.3275911)

           ; Save the sign of x
           (sign (if (< x 0) -1 1))
           (a (abs x))

           ; A&S formula 7.1.26
           (t (/ 1.0 (+ 1.0 (* p a))))
           (y (- 1.0 (* (+ (* (+ (* (+ (* (+ (* a5 t) a4) t) a3) t) a2) t) a1) t (exp (* (- a) a))))))

        (* sign y)))