root/arch/x86/math-emu/reg_mul.c

DEFINITIONS

1. FPU_mul

/*---------------------------------------------------------------------------+
 |  reg_mul.c                                                                |
 |                                                                           |
 | Multiply one FPU_REG by another, put the result in a destination FPU_REG. |
 |                                                                           |
 | Copyright (C) 1992,1993,1997                                              |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   billm@suburbia.net                              |
 |                                                                           |
 | Returns the tag of the result if no exceptions or errors occurred.        |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 | The destination may be any FPU_REG, including one of the source FPU_REGs. |
 +---------------------------------------------------------------------------*/

#include "fpu_emu.h"
#include "exception.h"
#include "reg_constant.h"
#include "fpu_system.h"

/*
  Multiply two registers to give a register result.
  The sources are st(deststnr) and (b,tagb,signb).
  The destination is st(deststnr).
  */
/* This routine must be called with non-empty source registers */
int FPU_mul(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
{
        FPU_REG *a = &st(deststnr);
        FPU_REG *dest = a;
        u_char taga = FPU_gettagi(deststnr);
        u_char saved_sign = getsign(dest);
        u_char sign = (getsign(a) ^ getsign(b));
        int tag;

        if (!(taga | tagb)) {
                /* Both regs Valid, this should be the most common case. */

                tag =
                    FPU_u_mul(a, b, dest, control_w, sign,
                              exponent(a) + exponent(b));
                if (tag < 0) {
                        setsign(dest, saved_sign);
                        return tag;
                }
                FPU_settagi(deststnr, tag);
                return tag;
        }

        if (taga == TAG_Special)
                taga = FPU_Special(a);
        if (tagb == TAG_Special)
                tagb = FPU_Special(b);

        if (((taga == TAG_Valid) && (tagb == TW_Denormal))
            || ((taga == TW_Denormal) && (tagb == TAG_Valid))
            || ((taga == TW_Denormal) && (tagb == TW_Denormal))) {
                FPU_REG x, y;
                if (denormal_operand() < 0)
                        return FPU_Exception;

                FPU_to_exp16(a, &x);
                FPU_to_exp16(b, &y);
                tag = FPU_u_mul(&x, &y, dest, control_w, sign,
                                exponent16(&x) + exponent16(&y));
                if (tag < 0) {
                        setsign(dest, saved_sign);
                        return tag;
                }
                FPU_settagi(deststnr, tag);
                return tag;
        } else if ((taga <= TW_Denormal) && (tagb <= TW_Denormal)) {
                if (((tagb == TW_Denormal) || (taga == TW_Denormal))
                    && (denormal_operand() < 0))
                        return FPU_Exception;

                /* Must have either both arguments == zero, or
                   one valid and the other zero.
                   The result is therefore zero. */
                FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
                /* The 80486 book says that the answer is +0, but a real
                   80486 behaves this way.
                   IEEE-754 apparently says it should be this way. */
                setsign(dest, sign);
                return TAG_Zero;
        }
        /* Must have infinities, NaNs, etc */
        else if ((taga == TW_NaN) || (tagb == TW_NaN)) {
                return real_2op_NaN(b, tagb, deststnr, &st(0));
        } else if (((taga == TW_Infinity) && (tagb == TAG_Zero))
                   || ((tagb == TW_Infinity) && (taga == TAG_Zero))) {
                return arith_invalid(deststnr); /* Zero*Infinity is invalid */
        } else if (((taga == TW_Denormal) || (tagb == TW_Denormal))
                   && (denormal_operand() < 0)) {
                return FPU_Exception;
        } else if (taga == TW_Infinity) {
                FPU_copy_to_regi(a, TAG_Special, deststnr);
                setsign(dest, sign);
                return TAG_Special;
        } else if (tagb == TW_Infinity) {
                FPU_copy_to_regi(b, TAG_Special, deststnr);
                setsign(dest, sign);
                return TAG_Special;
        }
#ifdef PARANOID
        else {
                EXCEPTION(EX_INTERNAL | 0x102);
                return FPU_Exception;
        }
#endif /* PARANOID */

        return 0;
}