[plt-scheme] modulo with real

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Mon May 16 13:42:20 EDT 2005

At Mon, 16 May 2005 18:05:29 +0200 (CEST), Bocdu jonf wrote:
> How can I express  " a modulo b" with dr scheme if  "a"  is a number (real or 
> not) and "b" is a real ?

Assuming that you want something like C's `fmod', you might use the
code in plt/collects/mzscheme/examples, "fmod.c" or "fmod-ez.c".

Here's a quick attempt directly in Scheme:

(define (mod a b)
  (with-handlers ([exn:fail? 
		   (lambda (exn) 
		     ;; Maybe failed because of inf/nan arguments:
		     (if (or (member a '(+inf.0 -inf.0 +nan.0))
			     (member b '(+inf.0 -inf.0 +nan.0)))
			 (raise exn)))])
    (let* ([ae (inexact->exact (abs a))]
	   [be (inexact->exact (abs b))]
	   [k (floor (/ ae be))]
	   [m ((if (negative? a) - +) (- ae (* be k)))])
      (if (or (inexact? a)
	      (inexact? b))
	  (exact->inexact m)


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