[Chicken-janitors] #1157: test egg 'approx-equal?' bug?

[Chicken Trac]

#1157: test egg 'approx-equal?' bug?
---------------------+------------------------------------------------------
 Reporter:  retroj   |       Owner:         
     Type:  defect   |      Status:  new    
 Priority:  major    |   Milestone:  someday
Component:  unknown  |     Version:  4.9.x  
 Keywords:           |  
---------------------+------------------------------------------------------
 There may be a bug in 'approx-equal?' in the test egg.

 I was puzzled as to why testing against an expected value of 0.0 always
 seems to fail, even with a large epsilon (1.0).

     (use test)
     (test 0.0 1e-18) => [FAIL]

 Here is the source code of 'approx-equal?' for reference:

     (define (approx-equal? a b epsilon)
       (cond
        ((> (abs a) (abs b))
         (approx-equal? b a epsilon))
        ((zero? b)
         (< (abs a) epsilon))
        (else
         (< (abs (/ (- a b) b)) epsilon))))

 I note that the conditional branch (zero? b), which is apparently a
 special case for testing against 0, will never be reached unless both a
 and b are 0, because if b is 0 the absolute value of any other number is
 greater, so the previous condition will catch it and flip a and b.

 Should that middle condition instead be the following?

        ((zero? a)
         (< (abs b) epsilon))

-- 
Ticket URL: <http://bugs.call-cc.org/ticket/1157>
CHICKEN Scheme <http://www.call-with-current-continuation.org/>
CHICKEN Scheme is a compiler for the Scheme programming language.