INFO: Detecting x86 Floating Point Coprocessor in Win32

MORE INFORMATION

One approach you can use to detect whether a coprocessor is present is to read the CR0 (System Control Register). This is not possible from Ring 3 application code under Windows NT, so a different approach is outlined below.

To determine whether a coprocessor is present on a computer using the x86 platform running Windows NT, you need to determine if the registry entry HKEY_LOCAL_MACHINE\\HARDWARE\\DESCRIPTION\\System\\FloatingPointProcessor is present. If this key is present, a numeric coprocessor is present.

On the MIPS and Alpha platforms, this registry key is not present because floating point support is built-in. The following function indicates whether a numeric coprocessor is present on Windows NT. If the function returns TRUE, a coprocessor is present. If the function returns FALSE, and GetLastError() indicates ERROR_RESOURCE_DATA_NOT_FOUND, a coprocessor is not present. Otherwise, an error occured while attempting to detect for a coprocessor. Some error checking is omitted, for brevity.

BOOL IsCoProcessorPresent(void)
{
    #define MY_ERROR_WRONG_OS 0x20000000
    HKEY hKey;
    SYSTEM_INFO SystemInfo;

    // return FALSE if we are not running under Windows NT
    // this should be expanded to cover alternative Win32 platforms

    if(!(GetVersion() & 0x7FFFFFFF))
    {
        SetLastError(MY_ERROR_WRONG_OS);
        return(FALSE);
    }

    // we return TRUE if we're not running on x86
    // other CPUs have built in floating-point, with no registry entry

    GetSystemInfo(&SystemInfo);

    if((SystemInfo.dwProcessorType != PROCESSOR_INTEL_386) &&
       (SystemInfo.dwProcessorType != PROCESSOR_INTEL_486) &&
       (SystemInfo.dwProcessorType != PROCESSOR_INTEL_PENTIUM))
    {
        return(TRUE);
    }

    if(RegOpenKeyEx(HKEY_LOCAL_MACHINE,

"HARDWARE\\DESCRIPTION\\System\\FloatingPointProcessor",

                    0,
                    KEY_EXECUTE,
                    &hKey) != ERROR_SUCCESS)
    {
        // GetLastError() will indicate ERROR_RESOURCE_DATA_NOT_FOUND
        // if we can't find the key.  This indicates no coprocessor present
        return(FALSE);
    }

    RegCloseKey(hKey);
    return(TRUE);
}