+++ /dev/null
-/*---------------------------------------------------------------------------+
- | 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;
-}
-
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