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

{
        denormalize(ptr, MIN_EXP);
        if (ptr->type != IFPF_IS_ZERO)
        {
        
                /* clear the extraneous bits */
                ptr->mantissa[3] &= 0xfff8;
/*              for (i=4; i<INTERNAL_FPF_PRECISION; i++)
                {
                        ptr->mantissa[i] = 0;
                }
*/
                /*
                ** Check for overflow
                */
                if ((unsigned)ptr->exp > MAX_EXP)
                {
                        SetInternalFPFInfinity(ptr, ptr->sign);
                }
        }
}
return;
}

/*******************************************************
**  ARITHMETIC OPERATIONS ON INTERNAL REPRESENTATION  **
*******************************************************/

/***************
** choose_nan **
****************
** Called by routines that are forced to perform math on
** a pair of NaN's.  This routine "selects" which NaN is
** to be returned.
*/
static void choose_nan(InternalFPF *x,
                InternalFPF *y,
                InternalFPF *z,
                int intel_flag)
{
int i;

/*
** Compare the two mantissas,
** return the larger.  Note that we will be emulating
** an 80387 in this operation.
*/
for (i=0; i<INTERNAL_FPF_PRECISION; i++)
{
        if (x->mantissa[i] > y->mantissa[i])
        {
                memmove((void *)x,(void *)z,sizeof(InternalFPF));
                return;
        }
        if (x->mantissa[i] < y->mantissa[i])
        {
                memmove((void *)y,(void *)z,sizeof(InternalFPF));
                return;
        }
}

/* 
** They are equal
*/
if (!intel_flag)
        /* if the operation is addition */
        memmove((void *)x,(void *)z,sizeof(InternalFPF));
else
        /* if the operation is multiplication */
        memmove((void *)y,(void *)z,sizeof(InternalFPF));
return;
}


/**********************
** AddSubInternalFPF **
***********************
** Adding or subtracting internal-representation numbers.
** Internal-representation numbers pointed to by x and y are
** added/subtracted and the result returned in z.
*/
static void AddSubInternalFPF(uchar operation,
                InternalFPF *x,
                InternalFPF *y,
                InternalFPF *z)
{
int exponent_difference;
u16 borrow;
u16 carry;
int i;
InternalFPF locx,locy;  /* Needed since we alter them */

/*
** Following big switch statement handles the
** various combinations of operand types.
*/
switch ((x->type * IFPF_TYPE_COUNT) + y->type)
{
case ZERO_ZERO:
        memmove((void *)x,(void *)z,sizeof(InternalFPF));
        if (x->sign ^ y->sign ^ operation)
        {
                z->sign = 0; /* positive */
        }
        break;

case NAN_ZERO:
case NAN_SUBNORMAL:
case NAN_NORMAL:
case NAN_INFINITY:
case SUBNORMAL_ZERO:
case NORMAL_ZERO:
case INFINITY_ZERO:
case INFINITY_SUBNORMAL:
case INFINITY_NORMAL:
        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 ZERO_SUBNORMAL:
case ZERO_NORMAL:
case ZERO_INFINITY:
case SUBNORMAL_INFINITY:
case NORMAL_INFINITY:
        memmove((void *)y,(void *)z,sizeof(InternalFPF));
        z->sign ^= operation;
        break;

case SUBNORMAL_SUBNORMAL:
case SUBNORMAL_NORMAL:
case NORMAL_SUBNORMAL:
case NORMAL_NORMAL:
        /*
        ** Copy x and y to locals, since we may have
        ** to alter them.
        */
        memmove((void *)&locx,(void *)x,sizeof(InternalFPF));
        memmove((void *)&locy,(void *)y,sizeof(InternalFPF));

        /* compute sum/difference */
        exponent_difference = locx.exp-locy.exp;
        if (exponent_difference == 0)
        {
                /* 
                ** locx.exp == locy.exp
                ** so, no shifting required
                */
                if (locx.type == IFPF_IS_SUBNORMAL ||
                  locy.type == IFPF_IS_SUBNORMAL)
                        z->type = IFPF_IS_SUBNORMAL;
                else
                        z->type = IFPF_IS_NORMAL;

                /* 
                ** Assume that locx.mantissa > locy.mantissa
                */
                z->sign = locx.sign;
                z->exp= locx.exp;
        }
        else
                if (exponent_difference > 0)
                {
                        /*
                        ** locx.exp > locy.exp
                        */
                        StickyShiftRightMant(&locy,
                                 exponent_difference);
                        z->type = locx.type;
                        z->sign = locx.sign;
                        z->exp = locx.exp;
                }
                else    /* if (exponent_difference < 0) */
                {
                        /*
                        ** locx.exp < locy.exp
                        */
                        StickyShiftRightMant(&locx,
                                -exponent_difference);
                        z->type = locy.type;
                        z->sign = locy.sign ^ operation;
                        z->exp = locy.exp;
                }

                if (locx.sign ^ locy.sign ^ operation)
                {
                        /* 
                        ** Signs are different, subtract mantissas
                        */
                        borrow = 0;
                        for (i=(INTERNAL_FPF_PRECISION-1); i>=0; i--)
                                Sub16Bits(&borrow,
                                        &z->mantissa[i],
                                        locx.mantissa[i],
                                        locy.mantissa[i]);

                        if (borrow)
                        {
                                /* The y->mantissa was larger than the
                                ** x->mantissa leaving a negative
                                ** result.  Change the result back to
                                ** an unsigned number and flip the
                                ** sign flag.
                                */
                                z->sign = locy.sign ^ operation;
                                borrow = 0;
                                for (i=(INTERNAL_FPF_PRECISION-1); i>=0; i--)
                                {
                                        Sub16Bits(&borrow,
                                                &z->mantissa[i],
                                                0,
                                                z->mantissa[i]);
                                }
                        }
                        else
                        {
                                /* The assumption made above
                                ** (i.e. x->mantissa >= y->mantissa)
                                ** was correct.  Therefore, do nothing.
                                ** z->sign = x->sign;
                                */
                        }

                        if (IsMantissaZero(z->mantissa))
                        {
                                z->type = IFPF_IS_ZERO;
                                z->sign = 0; /* positive */
                        }
                        else
                                if (locx.type == IFPF_IS_NORMAL ||
                                         locy.type == IFPF_IS_NORMAL)
                                {
                                        normalize(z);
                                }
                }
                else
                {
                        /* signs are the same, add mantissas */
                        carry = 0;
                        for (i=(INTERNAL_FPF_PRECISION-1); i>=0; i--)
                        {
                                Add16Bits(&carry,
                                        &z->mantissa[i],
                                        locx.mantissa[i],
                                        locy.mantissa[i]);
                        }

                        if (carry)
                        {
                                z->exp++;
                                carry=0;
                                ShiftMantRight1(&carry,z->mantissa);
                                z->mantissa[0] |= 0x8000;
                                z->type = IFPF_IS_NORMAL;
                        }
                        else
                                if (z->mantissa[0] & 0x8000)
                                        z->type = IFPF_IS_NORMAL;
        }
        break;

case INFINITY_INFINITY:
        SetInternalFPFNaN(z);
        break;

case NAN_NAN:
        choose_nan(x, y, z, 1);
        break;
}

/*
** All the math is done; time to round.
*/
RoundInternalFPF(z);
return;
}


/************************
** MultiplyInternalFPF **
*************************
** Two internal-representation numbers x and y are multiplied; the
** result is returned in z.
*/
static void MultiplyInternalFPF(InternalFPF *x,
                        InternalFPF *y,
                        InternalFPF *z)
{
int i;
int j;
u16 carry;
u16 extra_bits[INTERNAL_FPF_PRECISION];
InternalFPF locy;       /* Needed since this will be altered */
/*
** As in the preceding function, this large switch
** statement selects among the many combinations
** of operands.
*/
switch ((x->type * IFPF_TYPE_COUNT) + y->type)
{
case INFINITY_SUBNORMAL:
case INFINITY_NORMAL:
case INFINITY_INFINITY:
case ZERO_ZERO:
case ZERO_SUBNORMAL:
case ZERO_NORMAL:
        memmove((void *)x,(void *)z,sizeof(InternalFPF));
        z->sign ^= y->sign;
        break;

case SUBNORMAL_INFINITY:
case NORMAL_INFINITY:
case SUBNORMAL_ZERO:
case NORMAL_ZERO:
        memmove((void *)y,(void *)z,sizeof(InternalFPF));
        z->sign ^= x->sign;
        break;

case ZERO_INFINITY:
case INFINITY_ZERO:
        SetInternalFPFNaN(z);
        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 SUBNORMAL_NORMAL:
case NORMAL_SUBNORMAL:
case NORMAL_NORMAL:
        /*
        ** Make a local copy of the y number, since we will be
        ** altering it in the process of multiplying.
        */
        memmove((void *)&locy,(void *)y,sizeof(InternalFPF));

        /*
        ** Check for unnormal zero arguments
        */
        if (IsMantissaZero(x->mantissa) || IsMantissaZero(y->mantissa))
                SetInternalFPFInfinity(z, 0);

        /*
        ** Initialize the result
        */
        if (x->type == IFPF_IS_SUBNORMAL ||
            y->type == IFPF_IS_SUBNORMAL)
                z->type = IFPF_IS_SUBNORMAL;
        else
                z->type = IFPF_IS_NORMAL;

        z->sign = x->sign ^ y->sign;
        z->exp = x->exp + y->exp ;
        for (i=0; i<INTERNAL_FPF_PRECISION; i++)
        {
                z->mantissa[i] = 0;
                extra_bits[i] = 0;
        }

        for (i=0; i<(INTERNAL_FPF_PRECISION*16); i++)
        {
                /*
                ** Get rightmost bit of the multiplier
                */
                carry = 0;
                ShiftMantRight1(&carry, locy.mantissa);
                if (carry)
                {
                        /* 
                        ** Add the multiplicand to the product
                        */
                        carry = 0;
                        for (j=(INTERNAL_FPF_PRECISION-1); j>=0; j--)
                                Add16Bits(&carry,
                                        &z->mantissa[j],
                                        z->mantissa[j],
                                        x->mantissa[j]);
                }
                else
                {
                        carry = 0;
                }

                /* 
                ** Shift the product right.  Overflow bits get
                ** shifted into extra_bits.  We'll use it later
                ** to help with the "sticky" bit.
                */
                ShiftMantRight1(&carry, z->mantissa);
                ShiftMantRight1(&carry, extra_bits);
        }

        /*
        ** Normalize
        ** Note that we use a "special" normalization routine
        ** because we need to use the extra bits. (These are
        ** bits that may have been shifted off the bottom that
        ** we want to reclaim...if we can.
        */
        while ((z->mantissa[0] & 0x8000) == 0)
        {
                carry = 0;
                ShiftMantLeft1(&carry, extra_bits);
                ShiftMantLeft1(&carry, z->mantissa);
                z->exp--;
        }