=====Using 32-bit floating point values=====

//by Jon Ripley, August 2006//\\ \\ //BBC BASIC for Windows// stores floating point numbers in 40-bit and 64-bit resolutions and has no built-in support for 32-bit (single precision) floating point numbers. When using the Windows API and functions in third party DLLs it is sometimes necessary to use 32-bit floating point numbers. To ensure that single precision numbers are correctly passed to **SYS** calls they must be stored in integer variables which are also 32-bits wide.\\ \\  The following two functions are required to perform the necessary conversions:\\ \\ 

  * **FN_ConvertToSingle** converts a number to a single precision floating point value
  * **FN_ConvertFromSingle** converts a number from a single precision floating point value
\\ 
<code bb4w>
        DEF FN_ConvertToSingle(A#)
        LOCAL A%,P%
        PRIVATE F%
        IF F%=0 THEN
          DIM P% 10
          [OPT 2
          .F%
          mov esi,[ebp+2]   ; esi = pointer to A#
          mov edi,[ebp+7]   ; edi = pointer to A%
          fld qword [esi]   ; load indirect 64 bit real from esi
          fstp dword [edi]  ; store indirect 32 bit real to edi
          ret
          ]
        ENDIF
        A#*=1.0#
        CALL F%,A#,A%
        =A%

        DEF FN_ConvertFromSingle(A%)
        LOCAL A#,P%
        PRIVATE F%
        IF F%=0 THEN
          DIM P% 10
          [OPT 2
          .F%
          mov esi,[ebp+2]   ; esi = pointer to A%
          mov edi,[ebp+7]   ; edi = pointer to A#
          fld dword [esi]   ; load indirect 32 bit real from esi
          fstp qword [edi]  ; store indirect 64 bit real to edi
          ret
          ]
        ENDIF
        CALL F%,A%,A#
        =A#
</code>
\\ **Note:** **FN_ConvertToSingle** is the same routine as **FN_f4** from the supplied //D3DLIB// library, but the assembly language has been commented and the name has been changed for clarity.\\
----
\\ //by Richard Russell, November 2006//\\ \\  The above routines use assembly language code to perform the conversion. An alternative is to use Windows API functions as follows:\\ \\ 
<code bb4w>
        DEF FN_ConvertToSingle(A#)
        LOCAL A%
        PRIVATE F%
        IF F% = 0 THEN
          SYS "LoadLibrary", "OLEAUT32.DLL" TO F%
          SYS "GetProcAddress", F%, "VarR4FromR8" TO F%
        ENDIF
        A#*=1.0#
        SYS F%,!^A#,!(^A#+4),^A%
        =A%

        DEF FN_ConvertFromSingle(A%)
        LOCAL A#
        PRIVATE F%
        IF F% = 0 THEN
          SYS "LoadLibrary", "OLEAUT32.DLL" TO F%
          SYS "GetProcAddress", F%, "VarR8FromR4" TO F%
        ENDIF
        SYS F%,A%,^A#
        =A#
</code>
If speed is critical, use this conversion function:\\ 
<code bb4w>
        DEF FN_ConvertToSingle(A#)=USR(f4)
</code>
where the routine **f4** has been assembled previously as follows:\\ 
<code bb4w>
          .f4
          mov   ecx,[^A#+4]
          test  ecx,&FFFFFF00
          jnz   f4d
          movzx ecx,cl
          jecxz f4i
          mov   edx,[^A#]
          add   ecx,895
          rol   edx,1
          shld  ecx,edx,21
          shl   edx,20
          btr   edx,20
          rcr   ecx,1
          mov   [^A#],edx
          mov   [^A#+4],ecx
          .f4d
          push  eax
          fld   qword [^A#]
          fstp  dword [esp]
          pop   eax
          ret
          ;
          .f4i
          push  eax
          fild  dword [^A#]
          fstp  dword [esp]
          pop   eax
          ret
</code>
Ensure there is at least a 2048-byte gap between the code and any writable data, to prevent thrashing of the instruction cache.