histogram   xtlang

(bind-func histogram
  (lambda (hist:HistBin* buf:float* len lower upper nbins)
    (let ((current_bin:HistBin* null)
          (range (- upper lower)))
      (if (not (> range 0.))
          (begin
            (println "Error in histogram: range (- upper lower) must be greater than 0.0")
            null)
          (begin
            ;; setup the bins
            (doloop (i nbins)
              (tset! (pref-ptr hist i)
                     0
                     (+ lower (* (convert i) (/ range (convert nbins)))))
              (tset! (pref-ptr hist i)
                     1
                     0.))
            (doloop (i len)
              (set! current_bin
                    ;; use "mod nbins" to make sure it always goes
                    ;; into a valid slot in memory
                    (pref-ptr hist (% (convert (* (convert nbins float) (/ (- (pref buf i) lower) range)) i64) nbins)))
              (tset! current_bin 1 (+ (tref current_bin 1) 1.0)))
            hist)))))