ieeecvt.c

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/*
 * C O N V E R T   T O   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.
 */

#include "math.h"

#ifndef HUGE_VAL
#ifdef HUGE
#define HUGE_VAL HUGE
#else
/* WARNING: this is machine-dependent and should come from math.h */
#define HUGE_VAL 1.797693134862315e308
#endif /* HUGE */
#endif /*HUGE_VAL*/

# define FloatToUnsigned(f)      ((unsigned long)(((long)(f - 2147483648.0)) + 2147483647L) + 1)

void ConvertToIeeeExtended(double num, char *bytes)
{
    int    sign;
    int expon;
    double fMant, fsMant;
    unsigned long hiMant, loMant;

    if (num < 0) {
        sign = 0x8000;
        num *= -1;
    } else {
        sign = 0;
    }

    if (num == 0) {
        expon = 0; hiMant = 0; loMant = 0;
    }
    else {
        fMant = frexp(num, &expon);
        if ((expon > 16384) || !(fMant < 1)) {    /* Infinity or NaN */
            expon = sign|0x7FFF; hiMant = 0; loMant = 0; /* infinity */
        }
        else {    /* Finite */
            expon += 16382;
            if (expon < 0) {    /* denormalized */
                fMant = ldexp(fMant, expon);
                expon = 0;
            }
            expon |= sign;
            fMant = ldexp(fMant, 32);          
            fsMant = floor(fMant); 
            hiMant = FloatToUnsigned(fsMant);
            fMant = ldexp(fMant - fsMant, 32); 
            fsMant = floor(fMant); 
            loMant = FloatToUnsigned(fsMant);
        }
    }
    
    bytes[0] = (char) (expon >> 8);
    bytes[1] = (char) expon;
    bytes[2] = (char) (hiMant >> 24);
    bytes[3] = (char) (hiMant >> 16);
    bytes[4] = (char) (hiMant >> 8);
    bytes[5] = (char) hiMant;
    bytes[6] = (char) (loMant >> 24);
    bytes[7] = (char) (loMant >> 16);
    bytes[8] = (char) (loMant >> 8);
    bytes[9] = (char) loMant;
}


/*
 * 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(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;
}