zum leidigen Thema double

/*

 * C O N V E R T   F R O M   I E E E   E X T E N D E D  

 */

/* 

 * Copyright (C) 1988-1991 Apple Computer, Inc.

 * All rights reserved.

 *

 * Machine-independent I/O routines for IEEE floating-point numbers.

 *

 * NaN's and infinities are converted to HUGE_VAL or HUGE, which

 * happens to be infinity on IEEE machines.  Unfortunately, it is

 * impossible to preserve NaN's in a machine-independent way.

 * Infinities are, however, preserved on IEEE machines.

 *

 * These routines have been tested on the following machines:

 *    Apple Macintosh, MPW 3.1 C compiler

 *    Apple Macintosh, THINK C compiler

 *    Silicon Graphics IRIS, MIPS compiler

 *    Cray X/MP and Y/MP

 *    Digital Equipment VAX

 *

 *

 * Implemented by Malcolm Slaney and Ken Turkowski.

 *

 * Malcolm Slaney contributions during 1988-1990 include big- and little-

 * endian file I/O, conversion to and from Motorola's extended 80-bit

 * floating-point format, and conversions to and from IEEE single-

 * precision floating-point format.

 *

 * In 1991, Ken Turkowski implemented the conversions to and from

 * IEEE double-precision format, added more precision to the extended

 * conversions, and accommodated conversions involving +/- infinity,

 * NaN's, and denormalized numbers.

 */

#ifndef HUGE_VAL

# define HUGE_VAL HUGE

#endif /*HUGE_VAL*/

# define UnsignedToFloat(u)         (((double)((long)(u - 2147483647L - 1))) + 2147483648.0)

/****************************************************************

 * Extended precision IEEE floating-point conversion routine.

 ****************************************************************/

double ConvertFromIeeeExtended(bytes)

unsigned char *bytes;  /* LCN */

{

    double    f;

    int    expon;

    unsigned long hiMant, loMant;

    expon = ((bytes[0] & 0x7F) << 8) | (bytes[1] & 0xFF);

    hiMant    =    ((unsigned long)(bytes[2] & 0xFF) << 24)

            |    ((unsigned long)(bytes[3] & 0xFF) << 16)

            |    ((unsigned long)(bytes[4] & 0xFF) << 8)

            |    ((unsigned long)(bytes[5] & 0xFF));

    loMant    =    ((unsigned long)(bytes[6] & 0xFF) << 24)

            |    ((unsigned long)(bytes[7] & 0xFF) << 16)

            |    ((unsigned long)(bytes[8] & 0xFF) << 8)

            |    ((unsigned long)(bytes[9] & 0xFF));

    if (expon == 0 && hiMant == 0 && loMant == 0) {

        f = 0;

    }

    else {

        if (expon == 0x7FFF) {    /* Infinity or NaN */

            f = HUGE_VAL;

        }

        else {

            expon -= 16383;

            f  = ldexp(UnsignedToFloat(hiMant), expon-=31);

            f += ldexp(UnsignedToFloat(loMant), expon-=32);

        }

    }

    if (bytes[0] & 0x80)

        return -f;

    else

        return f;

}