Re: [Emacs-diffs] master 37940b3: min and max now return one of their arguments

[Paul Eggert]

Stefan Monnier wrote:
> I'm wondering what is the motivation for this change.

It avoids nonsensical behavior where 'min' and 'max' were inconsistent with '<' 
and '>'. Before the patch, (max A B) could return A even when (< A B) returned 
t. For example:

  (let* ((a 1e16)
         (b (1+ (floor a))))
    (list a b (max a b) (< a b) (if (< a b) b a)))

returned (1e+16 10000000000000001 1e+16 t 10000000000000001) on a 64-bit 
GNU/Linux host just before the patch was applied. In this example, '<' is 
behaving correctly since A is less than B, and 'max' is behaving incorrectly 
since it is returning the lesser of A and B. (Come to think of it, this example 
is clearer than what's in etc/NEWS, so I'll update etc/NEWS.)

In the old days Emacs could assume that every Emacs integer had an exact 
floating-point representation, so it was OK for functions like '<' and 'max' to 
convert integer arguments to floating-point before doing their comparisons since 
these conversions could not lose information. This is no longer true, and the 
low-level code now needs to be more careful when comparing fixnums to floats.