vsum   xtlang

(bind-func vsum
  (lambda (buf:double* len:i64)
    (let ((tot:double 0.) (i 0))
      (if (> len 1)
        (let ((chunks (/ len 2)) (vbuf:/2,double/* (cast buf)) (vtot:/2,double/* (salloc)))
          (vfill! vtot 0. 0.)
          (let ((totref (pref vtot 0)))
            (dotimes (i chunks)
                (set! totref (+ totref (pref-ptr vbuf i))))
            (set! tot (+ (vref totref 0) (vref totref 1))))
        (set! len (& len 1))
        (set! buf (pref-ptr buf (* i 2)))))
      (dotimes (i len)
        (set! tot (+ tot (pref buf i))))
      tot)))