[Chicken-users] three-way comparison functions in Chicken

[Sven . Hartrumpf]

Hi.

There are many algorithms whose good performance values rely on efficient
three-way comparison functions (e.g. sorting with removing duplicates).
For characters and numbers, the Scheme-only versions are fast enough, I guess:

(define char-compare3 (lambda (a b)
  (- (char->integer a) (char->integer b))))

(define number-compare3 (lambda (a b)
  (- a b)))

But for strings - I think - I would need support from the Scheme system
because the 1st implementation is very slow and the 2nd is still not optimal:
; 1st implementation

(define string-compare3 (lambda (a b)
  (let ((a-length (string-length a))
        (b-length (string-length b)))
    (or (string-compare32 a b 0 (min a-length b-length))
        (- a-length b-length)))
   ))

(define string-compare32 (lambda (a b pos l)
  (if (= pos l)
      #f
      (let ((result (- (char->integer (string-ref a pos)) (char->integer 
(string-ref b pos)))))
        (if (zero? result)
            (string-compare32 a b (+ pos 1) l)
            result)))))


; 2nd implementation

(define string-compare3 (lambda (a b)
  (if (string<? a b)
      -1
      (if (string=? a b)
          0
          1))
   ))

Would it make sense to have a new Chicken function, like string-compare3 ?
(Maybe not much more than a call to memcmp is needed.)

Background: I am trying to provide some more feedback for the sorting SRFI-32
(http://srfi.schemers.org/srfi-32/ ), including some experimental data.
(Especially in the area of two-way comparison functions vs. three-way
comparison functions.)

Greetings
Sven