Comment 0 for bug 1712697

1. Not sure if this is intended or not, but comparing two (quiet) NaN using "=" throws floating-point-invalid-operation; I would expect the result to be NIL, based on IEEE-754.

2. (= (sb-kernel:make-single-float #x7FFFFFFF) (sb-kernel:make-single-float #x7FFFFFFF))
; Evaluation aborted on #<FLOATING-POINT-INVALID-OPERATION {1006900C03}>.

3. sbcl --version
   SBCL 1.3.13.7.master.75-b464cda

4. *FEATURES*

(:EOS ALEXANDRIA.0.DEV::SEQUENCE-EMPTYP :SWANK :QUICKLISP
 :SB-BSD-SOCKETS-ADDRINFO :ASDF-PACKAGE-SYSTEM :ASDF3.1 :ASDF3 :ASDF2 :ASDF
 :OS-UNIX :NON-BASE-CHARS-EXIST-P :ASDF-UNICODE :64-BIT :64-BIT-REGISTERS
 :ALIEN-CALLBACKS :ANSI-CL :ASH-RIGHT-VOPS :C-STACK-IS-CONTROL-STACK
 :COMMON-LISP :COMPACT-INSTANCE-HEADER :COMPARE-AND-SWAP-VOPS
 :COMPLEX-FLOAT-VOPS :CYCLE-COUNTER :ELF :FLOAT-EQL-VOPS
 :FP-AND-PC-STANDARD-SAVE :GENCGC :IEEE-FLOATING-POINT :IMMOBILE-CODE
 :IMMOBILE-SPACE :INLINE-CONSTANTS :INTEGER-EQL-VOP :LARGEFILE :LINKAGE-TABLE
 :LINUX :LITTLE-ENDIAN :MEMORY-BARRIER-VOPS :MULTIPLY-HIGH-VOPS
 :OS-PROVIDES-BLKSIZE-T :OS-PROVIDES-DLADDR :OS-PROVIDES-DLOPEN
 :OS-PROVIDES-GETPROTOBY-R :OS-PROVIDES-POLL :OS-PROVIDES-PUTWC
 :OS-PROVIDES-SUSECONDS-T :PACKAGE-LOCAL-NICKNAMES :PRECISE-ARG-COUNT-ERROR
 :RAW-INSTANCE-INIT-VOPS :RAW-SIGNED-WORD :SB-AFTER-XC-CORE
 :SB-CORE-COMPRESSION :SB-DOC :SB-EVAL :SB-FUTEX :SB-LDB :SB-PACKAGE-LOCKS
 :SB-SIMD-PACK :SB-SOURCE-LOCATIONS :SB-TEST :SB-THREAD :SB-UNICODE
 :SB-XREF-FOR-INTERNALS :SBCL :STACK-ALLOCATABLE-CLOSURES
 :STACK-ALLOCATABLE-FIXED-OBJECTS :STACK-ALLOCATABLE-LISTS
 :STACK-ALLOCATABLE-VECTORS :STACK-GROWS-DOWNWARD-NOT-UPWARD :SYMBOL-INFO-VOPS
 :UNBIND-N-VOP :UNIX :UNWIND-TO-FRAME-AND-CALL-VOP :X86-64)

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I am in a Yak shaving process: I was using the IEEE-FLOATS library and noticed that SBCL defines custom floating-point operations in SB-EXT; I generated a NaN with MAKE-SINGLE-FLOAT and wanted to see what Slime's fancy inspector would do with that value. An exception occurred instead, which leads me to send a pull request (see commit https://github.com/slime/slime/commit/925dd2d85e6f0aadee78c9c08b51991bad8b12ca).

Now, I am wondering if this is really necessary: shouldn't TWO-ARG-= simply returns NIL when given two NaNs?