OS X / PowerPC failing test: remainder return -0.0

[cellularmitosis]

I recently added CHICKEN 5.3.0 to my package manager for OS X Tiger/PowerPC and Leopard/PowerPC: ​https://github.com/cellularmitosis/leopard.sh/commit/192014b920692434337783199742ceb217694f27

When I ran the tests, there was only one failure:

(FAIL) remainder: flo/flo: expected 0.0 but got -0.0

I also verified it by hand:

$ csi
CHICKEN
(c) 2008-2021, The CHICKEN Team
(c) 2000-2007, Felix L. Winkelmann
Version 5.3.0 (rev e31bbee5)
macosx-unix-gnu-ppc [ 32bit dload ]

Type ,? for help.
#;1> (remainder 1.0 1.0)
-0.0
#;2> 

Thanks for all of your work on CHICKEN!

[cellularmitosis]

Interestingly, 0.0 and -0.0 compare equal, so I'm not sure if this can actually cause a problem.

#;1> (= 0.0 -0.0)
#t

[sjamaan]

It shouldn't cause a problem in practice, I think. For dividing flonums we rely on the libc modf() function which is according to the standard is supposed to return the same sign as its input.

Perhaps you can test in a simple C function what modf(1.0, &x) returns and what it stores in x?

[cellularmitosis]

Surprisingly, modf(1.0, &x) puts 0.000000 in x.

[sjamaan]

Since I don't have access to a PPC machine anymore, I'm afraid you're on your own for debugging this. Perhaps you can add some printfs to C_s_a_i_remainder in runtime.c. It's the most-indented code for flonums - check what the values of dx, dy and tmp are, and what the result is of the calculation it does in the call to C_flonum, i.e. dx - tmp * dy.

[cellularmitosis]

thanks for the pointers!