reg_mul.c

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/*---------------------------------------------------------------------------+
 |  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   [email protected]                              |
 |                                                                           |
 | 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;
}