Validating (Invalid) Floating-Point

When a floating-point value becomes invalid due to overflows, etc., the easiest way to make it valid is stretch the value into a larger floating- point form, which becomes valid, and then store it back out as a valid form. Confusing?

The following is a code snippet that detects single-precision floating-point overflows. In this case, the value is radians.

 OFLOW_FIXUP fRads ; Overflow fixup 

Listing 8-6: incx86\vmp3DX86M.inc

 OFLOW_FIXUP    MACRO    arg1    mov   eax,DWORD PTR arg1    ; 03F800000h = 1.0f   0BF800000h=1.0    and   eax,07F800000h    cmp   eax,07F800000h        ;Check for an non-zero exponent!    jne   $ok    mov   eax,DWORD PTR arg1    call FixupReal4 $ok:                           ; ST(0)= value endm 

 

To fix the overflow of a single-precision floating-point value, it can be expanded to double extended-precision floating-point or double-precision floating-point, such as in the following code snippet.

Listing 8-7: FixupReal4

 ;  Fixup Real4 (float) ;        eax=bad float ; NOTE: ST(0) already contains the float!!!     FixupReal4 proc near    fstp  qword ptr [esp810]        ; Save Real8 (double) & pop ST(0)     ; Build a Real10        mov     eax,[esp810+4]          ; Hi    or      eax,7FFF0000h             ; Set Real8 (Double)    mov     dword ptr [esp10+6],eax  ; 7FFFXXXX????????????        mov     eax,[esp810+4]          ; Real8 Hi    mov     ecx,[esp810+0]          ; Real8 Lo    shld    eax,ecx,11    shl     ecx,11    mov     dword ptr [esp10+4],eax  ; 7FFFHHHHHHHH????????    mov     dword ptr [esp10+0],ecx  ; FFFHHHHHHHHLLLLLLLL    fld     tbyte ptr [esp10+0]      ; Load Real10        ret    ; ST(0)=value FixupReal4 endp