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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 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;
}
|
