emfloat.c

来自「开放源码的编译器open watcom 1.6.0版的源代码」· C语言 代码 · 共 1,275 行 · 第 1/3 页

        /*
        ** Set the sticky bit if any bits set in extra bits.
        */
        if (IsMantissaZero(extra_bits))
        {
                z->mantissa[INTERNAL_FPF_PRECISION-1] |= 1;
        }
        break;

case NAN_NAN:
        choose_nan(x, y, z, 0);
        break;
}

/*
** All math done...do rounding.
*/
RoundInternalFPF(z);
return;
}


/**********************
** DivideInternalFPF **
***********************
** Divide internal FPF number x by y.  Return result in z.
*/
static void DivideInternalFPF(InternalFPF *x, 
                        InternalFPF *y, 
                        InternalFPF *z)
{
int i;
int j;
u16 carry;
u16 extra_bits[INTERNAL_FPF_PRECISION];
InternalFPF locx;       /* Local for x number */

/*
** As with preceding function, the following switch
** statement selects among the various possible
** operands.
*/
switch ((x->type * IFPF_TYPE_COUNT) + y->type)
{
case ZERO_ZERO:
case INFINITY_INFINITY:
        SetInternalFPFNaN(z);
        break;

case ZERO_SUBNORMAL:
case ZERO_NORMAL:
        if (IsMantissaZero(y->mantissa))
        {
                SetInternalFPFNaN(z);
                break;
        }

case ZERO_INFINITY:
case SUBNORMAL_INFINITY:
case NORMAL_INFINITY:
        SetInternalFPFZero(z, x->sign ^ y->sign);
        break;

case SUBNORMAL_ZERO:
case NORMAL_ZERO:
        if (IsMantissaZero(x->mantissa))
        {
                SetInternalFPFNaN(z);
                break;
        }

case INFINITY_ZERO:
case INFINITY_SUBNORMAL:
case INFINITY_NORMAL:
        SetInternalFPFInfinity(z, 0);
        z->sign = x->sign ^ y->sign;
        break;

case NAN_ZERO:
case NAN_SUBNORMAL:
case NAN_NORMAL:
case NAN_INFINITY:
        memmove((void *)x,(void *)z,sizeof(InternalFPF));
        break;

case ZERO_NAN:
case SUBNORMAL_NAN:
case NORMAL_NAN:
case INFINITY_NAN:
        memmove((void *)y,(void *)z,sizeof(InternalFPF));
        break;

case SUBNORMAL_SUBNORMAL:
case NORMAL_SUBNORMAL:
case SUBNORMAL_NORMAL:
case NORMAL_NORMAL:
        /*
        ** Make local copy of x number, since we'll be
        ** altering it in the process of dividing.
        */
        memmove((void *)&locx,(void *)x,sizeof(InternalFPF));

        /* 
        ** Check for unnormal zero arguments
        */
        if (IsMantissaZero(locx.mantissa))
        {
                if (IsMantissaZero(y->mantissa))
                        SetInternalFPFNaN(z);
                else
                        SetInternalFPFZero(z, 0);
                break;
        }
        if (IsMantissaZero(y->mantissa))
        {
                SetInternalFPFInfinity(z, 0);
                break;
        }

        /* 
        ** Initialize the result
        */
        z->type = x->type;
        z->sign = x->sign ^ y->sign;
        z->exp = x->exp - y->exp +
                        ((INTERNAL_FPF_PRECISION * 16 * 2));
        for (i=0; i<INTERNAL_FPF_PRECISION; i++)
        {
                z->mantissa[i] = 0;
                extra_bits[i] = 0;
        }

        while ((z->mantissa[0] & 0x8000) == 0)
        {
                carry = 0;
                ShiftMantLeft1(&carry, locx.mantissa);
                ShiftMantLeft1(&carry, extra_bits);

                /* 
                ** Time to subtract yet?
                */
                if (carry == 0)
                        for (j=0; j<INTERNAL_FPF_PRECISION; j++)
                        {
                                if (y->mantissa[j] > extra_bits[j])
                                {
                                        carry = 0;
                                        goto no_subtract;
                                }
                                if (y->mantissa[j] < extra_bits[j])
                                        break;
                        }
                /* 
                ** Divisor (y) <= dividend (x), subtract
                */
                carry = 0;
                for (j=(INTERNAL_FPF_PRECISION-1); j>=0; j--)
                        Sub16Bits(&carry,
                                &extra_bits[j],
                                extra_bits[j],
                                y->mantissa[j]);
                carry = 1;      /* 1 shifted into quotient */
        no_subtract:
                ShiftMantLeft1(&carry, z->mantissa);
                z->exp--;
        }
        break;

case NAN_NAN:
        choose_nan(x, y, z, 0);
        break;
}

/*
** Math complete...do rounding
*/
RoundInternalFPF(z);
}

/**********************
** LongToInternalFPF **
***********************
** Convert a signed long integer into an internal FPF number.
*/
static void LongToInternalFPF(long mylong,
                InternalFPF *dest)
{
int i;          /* Index */
u16 myword;     /* Used to hold converted stuff */
/*
** Save the sign and get the absolute value.  This will help us
** with 64-bit machines, since we use only the lower 32
** bits just in case.
*/
if(mylong<0L)
{       dest->sign=1;
        mylong=0L-mylong;
}
else
        dest->sign=0;
/*
** Prepare the destination floating point number
*/
dest->type=IFPF_IS_NORMAL;
for(i=0;i<INTERNAL_FPF_PRECISION;i++)
        dest->mantissa[i]=0;

/*
** See if we've got a zero.  If so, make the resultant FP
** number a true zero and go home.
*/
if(mylong==0)
{       dest->type=IFPF_IS_ZERO;
        dest->exp=0;
        return;
}

/*
** Not a true zero.  Set the exponent to 32 (internal FPFs have
** no bias) and load the low and high words into their proper
** locations in the mantissa.  Then normalize.  The action of
** normalizing slides the mantissa bits into place and sets
** up the exponent properly.
*/
dest->exp=32;
myword=(u16)((mylong >> 16) & 0xFFFFL);
dest->mantissa[0]=myword;
myword=(u16)(mylong & 0xFFFFL);
dest->mantissa[1]=myword;
normalize(dest);
return;
}

#if 0
/************************
** InternalFPFToString **
*************************
** FOR DEBUG PURPOSES
** This routine converts an internal floating point representation
** number to a string.  Used in debugging the package.
** Returns length of converted number.
** NOTE: dest must point to a buffer big enough to hold the
**  result.  Also, this routine does append a null (an effect
**  of using the sprintf() function).  It also returns
**  a length count.
** NOTE: This routine returns 5 significant digits.  Thats
**  about all I feel safe with, given the method of
**  conversion.  It should be more than enough for programmers
**  to determine whether the package is properly ported.
*/
static int InternalFPFToString(char *dest,
                InternalFPF *src)
{
InternalFPF locFPFNum;          /* Local for src (will be altered) */
InternalFPF IFPF10;             /* Floating-point 10 */
InternalFPF IFPFComp;           /* For doing comparisons */
int msign;                      /* Holding for mantissa sign */
int expcount;                   /* Exponent counter */
int ccount;                     /* Character counter */
int i,j,k;                      /* Index */
u16 carryaccum;                 /* Carry accumulator */
u16 mycarry;                    /* Local for carry */

/*
** Check first for the simple things...Nan, Infinity, Zero.
** If found, copy the proper string in and go home.
*/
switch(src->type)
{
        case IFPF_IS_NAN:
                memcpy(dest,"NaN",3);
                return(3);

        case IFPF_IS_INFINITY:
                if(src->sign==0)
                        memcpy(dest,"+Inf",4);
                else
                        memcpy(dest,"-Inf",4);
                return(4);

        case IFPF_IS_ZERO:
                if(src->sign==0)
                        memcpy(dest,"+0",2);
                else
                        memcpy(dest,"-0",2);
                return(2);
}

/*
** Move the internal number into our local holding area, since
** we'll be altering it to print it out.
*/
memcpy((void *)&locFPFNum,(void *)src,sizeof(InternalFPF));

/*
** Set up a floating-point 10...which we'll use a lot in a minute.
*/
LongToInternalFPF(10L,&IFPF10);

/*
** Save the mantissa sign and make it positive.
*/
msign=src->sign;
src->sign=0;

expcount=0;             /* Init exponent counter */

/*
** See if the number is less than 10.  If so, multiply
** the number repeatedly by 10 until it's not.   For each
** multiplication, decrement a counter so we can keep track
** of the exponent.
*/
while(1)
{       AddSubInternalFPF(1,&locFPFNum,&IFPF10,&IFPFComp);
        if(IFPFComp.sign==0) break;
        MultiplyInternalFPF(&locFPFNum,&IFPF10,&IFPFComp);
        expcount--;
        memcpy((void *)&locFPFNum,(void *)&IFPFComp,sizeof(InternalFPF));
}

/*
** Do the reverse of the above.  As long as the number is
** greater than or equal to 10, divide it by 10.  Increment the
** exponent counter for each multiplication.
*/
while(1)
{
        AddSubInternalFPF(1,&locFPFNum,&IFPF10,&IFPFComp);
        if(IFPFComp.sign!=0) break;
        DivideInternalFPF(&locFPFNum,&IFPF10,&IFPFComp);
        expcount++;
        memcpy((void *)&locFPFNum,(void *)&IFPFComp,sizeof(InternalFPF));
}

/*
** About time to start storing things.  First, store the
** mantissa sign.
*/
ccount=1;               /* Init character counter */
if(msign==0)
        *dest++='+';
else
        *dest++='-';

/*
** At this point we know that the number is in the range
** 10 > n >=1.  We need to "strip digits" out of the
** mantissa.  We do this by treating the mantissa as
** an integer and multiplying by 10. (Not a floating-point
** 10, but an integer 10.  Since this is debug code and we
** could care less about speed, we'll do it the stupid
** way and simply add the number to itself 10 times.
** Anything that makes it to the left of the implied binary point
** gets stripped off and emitted.  We'll do this for
** 5 significant digits (which should be enough to
** verify things).
*/
/*
** Re-position radix point
*/
carryaccum=0;
while(locFPFNum.exp>0)
{
        mycarry=0;
        ShiftMantLeft1(&mycarry,locFPFNum.mantissa);
        carryaccum=(carryaccum<<1);
        if(mycarry) carryaccum++;
        locFPFNum.exp--;
}

while(locFPFNum.exp<0)
{
        mycarry=0;
        ShiftMantRight1(&mycarry,locFPFNum.mantissa);
        locFPFNum.exp++;
}

for(i=0;i<6;i++)
        if(i==1)
        {       /* Emit decimal point */
                *dest++='.';
                ccount++;
        }
        else
        {       /* Emit a digit */
                *dest++=('0'+carryaccum);
                ccount++;

                carryaccum=0;
                memcpy((void *)&IFPF10,
                        (void *)&locFPFNum,
                        sizeof(InternalFPF));

                /* Do multiply via repeated adds */
                for(j=0;j<9;j++)
                {
                        mycarry=0;
                        for(k=(INTERNAL_FPF_PRECISION-1);k>=0;k--)              
                                Add16Bits(&mycarry,&(IFPFComp.mantissa[k]),
                                        locFPFNum.mantissa[k],
                                        IFPF10.mantissa[k]);
                        carryaccum+=mycarry ? 1 : 0;
                        memcpy((void *)&locFPFNum,
                                (void *)&IFPFComp,
                                sizeof(InternalFPF));
                }
        }
        
/*
** Now move the 'E', the exponent sign, and the exponent
** into the string.
*/
*dest++='E';

ccount+=sprintf(dest,"%4d",expcount);

/*
** All done, go home.
*/
return(ccount);

}
#endif