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|
/*---------------------------------------------------------------------------+
| reg_add_sub.c |
| |
| Functions to add or subtract two registers and put the result in a third. |
| |
| Copyright (C) 1992,1993,1997 |
| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
| E-mail billm@suburbia.net |
| |
| |
+---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------+
| For each function, the destination may be any FPU_REG, including one of |
| the source FPU_REGs. |
| Each function returns 0 if the answer is o.k., otherwise a non-zero |
| value is returned, indicating either an exception condition or an |
| internal error. |
+---------------------------------------------------------------------------*/
#include "exception.h"
#include "reg_constant.h"
#include "fpu_emu.h"
#include "control_w.h"
#include "fpu_system.h"
static
int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
FPU_REG const *b, u_char tagb, u_char signb,
FPU_REG *dest, int deststnr, int control_w);
/*
Operates on st(0) and st(n), or on st(0) and temporary data.
The destination must be one of the source st(x).
*/
int FPU_add(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
{
FPU_REG *a = &st(0);
FPU_REG *dest = &st(deststnr);
u_char signb = getsign(b);
u_char taga = FPU_gettag0();
u_char signa = getsign(a);
u_char saved_sign = getsign(dest);
int diff, tag, expa, expb;
if ( !(taga | tagb) )
{
expa = exponent(a);
expb = exponent(b);
valid_add:
/* Both registers are valid */
if (!(signa ^ signb))
{
/* signs are the same */
tag = FPU_u_add(a, b, dest, control_w, signa, expa, expb);
}
else
{
/* The signs are different, so do a subtraction */
diff = expa - expb;
if (!diff)
{
diff = a->sigh - b->sigh; /* This works only if the ms bits
are identical. */
if (!diff)
{
diff = a->sigl > b->sigl;
if (!diff)
diff = -(a->sigl < b->sigl);
}
}
if (diff > 0)
{
tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
}
else if ( diff < 0 )
{
tag = FPU_u_sub(b, a, dest, control_w, signb, expb, expa);
}
else
{
FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
/* sign depends upon rounding mode */
setsign(dest, ((control_w & CW_RC) != RC_DOWN)
? SIGN_POS : SIGN_NEG);
return TAG_Zero;
}
}
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);
a = &x;
b = &y;
expa = exponent16(a);
expb = exponent16(b);
goto valid_add;
}
if ( (taga == TW_NaN) || (tagb == TW_NaN) )
{
if ( deststnr == 0 )
return real_2op_NaN(b, tagb, deststnr, a);
else
return real_2op_NaN(a, taga, deststnr, a);
}
return add_sub_specials(a, taga, signa, b, tagb, signb,
dest, deststnr, control_w);
}
/* Subtract b from a. (a-b) -> dest */
int FPU_sub(int flags, int rm, int control_w)
{
FPU_REG const *a, *b;
FPU_REG *dest;
u_char taga, tagb, signa, signb, saved_sign, sign;
int diff, tag = 0, expa, expb, deststnr;
a = &st(0);
taga = FPU_gettag0();
deststnr = 0;
if ( flags & LOADED )
{
b = (FPU_REG *)rm;
tagb = flags & 0x0f;
}
else
{
b = &st(rm);
tagb = FPU_gettagi(rm);
if ( flags & DEST_RM )
deststnr = rm;
}
signa = getsign(a);
signb = getsign(b);
if ( flags & REV )
{
signa ^= SIGN_NEG;
signb ^= SIGN_NEG;
}
dest = &st(deststnr);
saved_sign = getsign(dest);
if ( !(taga | tagb) )
{
expa = exponent(a);
expb = exponent(b);
valid_subtract:
/* Both registers are valid */
diff = expa - expb;
if (!diff)
{
diff = a->sigh - b->sigh; /* Works only if ms bits are identical */
if (!diff)
{
diff = a->sigl > b->sigl;
if (!diff)
diff = -(a->sigl < b->sigl);
}
}
switch ( (((int)signa)*2 + signb) / SIGN_NEG )
{
case 0: /* P - P */
case 3: /* N - N */
if (diff > 0)
{
/* |a| > |b| */
tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
}
else if ( diff == 0 )
{
FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
/* sign depends upon rounding mode */
setsign(dest, ((control_w & CW_RC) != RC_DOWN)
? SIGN_POS : SIGN_NEG);
return TAG_Zero;
}
else
{
sign = signa ^ SIGN_NEG;
tag = FPU_u_sub(b, a, dest, control_w, sign, expb, expa);
}
break;
case 1: /* P - N */
tag = FPU_u_add(a, b, dest, control_w, SIGN_POS, expa, expb);
break;
case 2: /* N - P */
tag = FPU_u_add(a, b, dest, control_w, SIGN_NEG, expa, expb);
break;
#ifdef PARANOID
default:
EXCEPTION(EX_INTERNAL|0x111);
return -1;
#endif
}
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);
a = &x;
b = &y;
expa = exponent16(a);
expb = exponent16(b);
goto valid_subtract;
}
if ( (taga == TW_NaN) || (tagb == TW_NaN) )
{
FPU_REG const *d1, *d2;
if ( flags & REV )
{
d1 = b;
d2 = a;
}
else
{
d1 = a;
d2 = b;
}
if ( flags & LOADED )
return real_2op_NaN(b, tagb, deststnr, d1);
if ( flags & DEST_RM )
return real_2op_NaN(a, taga, deststnr, d2);
else
return real_2op_NaN(b, tagb, deststnr, d2);
}
return add_sub_specials(a, taga, signa, b, tagb, signb ^ SIGN_NEG,
dest, deststnr, control_w);
}
static
int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
FPU_REG const *b, u_char tagb, u_char signb,
FPU_REG *dest, int deststnr, int control_w)
{
if ( ((taga == TW_Denormal) || (tagb == TW_Denormal))
&& (denormal_operand() < 0) )
return FPU_Exception;
if (taga == TAG_Zero)
{
if (tagb == TAG_Zero)
{
/* Both are zero, result will be zero. */
u_char different_signs = signa ^ signb;
FPU_copy_to_regi(a, TAG_Zero, deststnr);
if ( different_signs )
{
/* Signs are different. */
/* Sign of answer depends upon rounding mode. */
setsign(dest, ((control_w & CW_RC) != RC_DOWN)
? SIGN_POS : SIGN_NEG);
}
else
setsign(dest, signa); /* signa may differ from the sign of a. */
return TAG_Zero;
}
else
{
reg_copy(b, dest);
if ( (tagb == TW_Denormal) && (b->sigh & 0x80000000) )
{
/* A pseudoDenormal, convert it. */
addexponent(dest, 1);
tagb = TAG_Valid;
}
else if ( tagb > TAG_Empty )
tagb = TAG_Special;
setsign(dest, signb); /* signb may differ from the sign of b. */
FPU_settagi(deststnr, tagb);
return tagb;
}
}
else if (tagb == TAG_Zero)
{
reg_copy(a, dest);
if ( (taga == TW_Denormal) && (a->sigh & 0x80000000) )
{
/* A pseudoDenormal */
addexponent(dest, 1);
taga = TAG_Valid;
}
else if ( taga > TAG_Empty )
taga = TAG_Special;
setsign(dest, signa); /* signa may differ from the sign of a. */
FPU_settagi(deststnr, taga);
return taga;
}
else if (taga == TW_Infinity)
{
if ( (tagb != TW_Infinity) || (signa == signb) )
{
FPU_copy_to_regi(a, TAG_Special, deststnr);
setsign(dest, signa); /* signa may differ from the sign of a. */
return taga;
}
/* Infinity-Infinity is undefined. */
return arith_invalid(deststnr);
}
else if (tagb == TW_Infinity)
{
FPU_copy_to_regi(b, TAG_Special, deststnr);
setsign(dest, signb); /* signb may differ from the sign of b. */
return tagb;
}
#ifdef PARANOID
EXCEPTION(EX_INTERNAL|0x101);
#endif
return FPU_Exception;
}
|
