Transform SIGNUM for double-floats

[Michał "phoe" Herda]

I request an implementation of SIGNUM specialized for double-floats.

Simplified example of current behavior (SBCL 2.0.10 on Linux amd64):

(defun foo (qx)
  (declare (optimize speed)
           (double-float qx))
  (signum (* qx qx)))

; file: /tmp/slime7JzwHT
; in: DEFUN FOO
; (SIGNUM (* QX QX))
;
; note: doing float to pointer coercion (cost 13)
;
; compilation unit finished
; printed 1 note

(A non-simplified example processes the result of SIGNUM further, so it's not a matter of boxing it again as a return value.)

Krystof on #sbcl mentioned that a wishlist ticket for a SIGNUM transform would be okay, so here it is.

[Douglas Katzman (dougk)]

https://sourceforge.net/p/sbcl/sbcl/ci/e94b13a00de5830ab2c1ce82c507d223abe2bbee/

[Michał "phoe" Herda (phoe-krk)]

Thanks!