334 lines
8.6 KiB
C
334 lines
8.6 KiB
C
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/*---------------------------------------------------------------------------+
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| reg_add_sub.c |
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| Functions to add or subtract two registers and put the result in a third. |
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| Copyright (C) 1992,1993,1997 |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
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| E-mail billm@suburbia.net |
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+---------------------------------------------------------------------------*/
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/*---------------------------------------------------------------------------+
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| For each function, the destination may be any FPU_REG, including one of |
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| the source FPU_REGs. |
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| Each function returns 0 if the answer is o.k., otherwise a non-zero |
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| value is returned, indicating either an exception condition or an |
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| internal error. |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "reg_constant.h"
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#include "fpu_emu.h"
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#include "control_w.h"
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#include "fpu_system.h"
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static
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int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
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FPU_REG const *b, u_char tagb, u_char signb,
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FPU_REG * dest, int deststnr, int control_w);
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/*
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Operates on st(0) and st(n), or on st(0) and temporary data.
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The destination must be one of the source st(x).
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*/
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int FPU_add(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
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{
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FPU_REG *a = &st(0);
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FPU_REG *dest = &st(deststnr);
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u_char signb = getsign(b);
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u_char taga = FPU_gettag0();
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u_char signa = getsign(a);
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u_char saved_sign = getsign(dest);
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int diff, tag, expa, expb;
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if (!(taga | tagb)) {
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expa = exponent(a);
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expb = exponent(b);
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valid_add:
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/* Both registers are valid */
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if (!(signa ^ signb)) {
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/* signs are the same */
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tag =
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FPU_u_add(a, b, dest, control_w, signa, expa, expb);
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} else {
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/* The signs are different, so do a subtraction */
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diff = expa - expb;
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if (!diff) {
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diff = a->sigh - b->sigh; /* This works only if the ms bits
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are identical. */
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if (!diff) {
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diff = a->sigl > b->sigl;
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if (!diff)
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diff = -(a->sigl < b->sigl);
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}
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}
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if (diff > 0) {
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tag =
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FPU_u_sub(a, b, dest, control_w, signa,
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expa, expb);
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} else if (diff < 0) {
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tag =
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FPU_u_sub(b, a, dest, control_w, signb,
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expb, expa);
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} else {
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FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
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/* sign depends upon rounding mode */
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setsign(dest, ((control_w & CW_RC) != RC_DOWN)
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? SIGN_POS : SIGN_NEG);
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return TAG_Zero;
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}
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}
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if (tag < 0) {
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setsign(dest, saved_sign);
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return tag;
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}
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FPU_settagi(deststnr, tag);
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return tag;
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}
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if (taga == TAG_Special)
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taga = FPU_Special(a);
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if (tagb == TAG_Special)
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tagb = FPU_Special(b);
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if (((taga == TAG_Valid) && (tagb == TW_Denormal))
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|| ((taga == TW_Denormal) && (tagb == TAG_Valid))
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|| ((taga == TW_Denormal) && (tagb == TW_Denormal))) {
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FPU_REG x, y;
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if (denormal_operand() < 0)
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return FPU_Exception;
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FPU_to_exp16(a, &x);
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FPU_to_exp16(b, &y);
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a = &x;
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b = &y;
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expa = exponent16(a);
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expb = exponent16(b);
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goto valid_add;
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}
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if ((taga == TW_NaN) || (tagb == TW_NaN)) {
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if (deststnr == 0)
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return real_2op_NaN(b, tagb, deststnr, a);
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else
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return real_2op_NaN(a, taga, deststnr, a);
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}
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return add_sub_specials(a, taga, signa, b, tagb, signb,
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dest, deststnr, control_w);
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}
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/* Subtract b from a. (a-b) -> dest */
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int FPU_sub(int flags, int rm, int control_w)
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{
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FPU_REG const *a, *b;
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FPU_REG *dest;
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u_char taga, tagb, signa, signb, saved_sign, sign;
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int diff, tag = 0, expa, expb, deststnr;
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a = &st(0);
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taga = FPU_gettag0();
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deststnr = 0;
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if (flags & LOADED) {
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b = (FPU_REG *) rm;
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tagb = flags & 0x0f;
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} else {
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b = &st(rm);
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tagb = FPU_gettagi(rm);
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if (flags & DEST_RM)
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deststnr = rm;
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}
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signa = getsign(a);
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signb = getsign(b);
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if (flags & REV) {
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signa ^= SIGN_NEG;
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signb ^= SIGN_NEG;
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}
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dest = &st(deststnr);
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saved_sign = getsign(dest);
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if (!(taga | tagb)) {
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expa = exponent(a);
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expb = exponent(b);
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valid_subtract:
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/* Both registers are valid */
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diff = expa - expb;
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if (!diff) {
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diff = a->sigh - b->sigh; /* Works only if ms bits are identical */
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if (!diff) {
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diff = a->sigl > b->sigl;
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if (!diff)
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diff = -(a->sigl < b->sigl);
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}
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}
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switch ((((int)signa) * 2 + signb) / SIGN_NEG) {
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case 0: /* P - P */
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case 3: /* N - N */
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if (diff > 0) {
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/* |a| > |b| */
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tag =
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FPU_u_sub(a, b, dest, control_w, signa,
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expa, expb);
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} else if (diff == 0) {
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FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
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/* sign depends upon rounding mode */
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setsign(dest, ((control_w & CW_RC) != RC_DOWN)
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? SIGN_POS : SIGN_NEG);
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return TAG_Zero;
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} else {
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sign = signa ^ SIGN_NEG;
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tag =
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FPU_u_sub(b, a, dest, control_w, sign, expb,
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expa);
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}
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break;
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case 1: /* P - N */
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tag =
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FPU_u_add(a, b, dest, control_w, SIGN_POS, expa,
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expb);
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break;
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case 2: /* N - P */
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tag =
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FPU_u_add(a, b, dest, control_w, SIGN_NEG, expa,
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expb);
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break;
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#ifdef PARANOID
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default:
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EXCEPTION(EX_INTERNAL | 0x111);
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return -1;
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#endif
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}
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if (tag < 0) {
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setsign(dest, saved_sign);
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return tag;
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}
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FPU_settagi(deststnr, tag);
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return tag;
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}
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if (taga == TAG_Special)
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taga = FPU_Special(a);
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if (tagb == TAG_Special)
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tagb = FPU_Special(b);
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if (((taga == TAG_Valid) && (tagb == TW_Denormal))
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|| ((taga == TW_Denormal) && (tagb == TAG_Valid))
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|| ((taga == TW_Denormal) && (tagb == TW_Denormal))) {
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FPU_REG x, y;
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if (denormal_operand() < 0)
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return FPU_Exception;
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FPU_to_exp16(a, &x);
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FPU_to_exp16(b, &y);
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a = &x;
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b = &y;
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expa = exponent16(a);
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expb = exponent16(b);
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goto valid_subtract;
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}
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if ((taga == TW_NaN) || (tagb == TW_NaN)) {
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FPU_REG const *d1, *d2;
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if (flags & REV) {
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d1 = b;
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d2 = a;
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} else {
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d1 = a;
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d2 = b;
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}
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if (flags & LOADED)
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return real_2op_NaN(b, tagb, deststnr, d1);
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if (flags & DEST_RM)
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return real_2op_NaN(a, taga, deststnr, d2);
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else
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return real_2op_NaN(b, tagb, deststnr, d2);
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}
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return add_sub_specials(a, taga, signa, b, tagb, signb ^ SIGN_NEG,
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dest, deststnr, control_w);
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}
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static
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int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
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FPU_REG const *b, u_char tagb, u_char signb,
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FPU_REG * dest, int deststnr, int control_w)
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{
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if (((taga == TW_Denormal) || (tagb == TW_Denormal))
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&& (denormal_operand() < 0))
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return FPU_Exception;
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if (taga == TAG_Zero) {
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if (tagb == TAG_Zero) {
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/* Both are zero, result will be zero. */
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u_char different_signs = signa ^ signb;
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FPU_copy_to_regi(a, TAG_Zero, deststnr);
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if (different_signs) {
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/* Signs are different. */
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/* Sign of answer depends upon rounding mode. */
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setsign(dest, ((control_w & CW_RC) != RC_DOWN)
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? SIGN_POS : SIGN_NEG);
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} else
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setsign(dest, signa); /* signa may differ from the sign of a. */
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return TAG_Zero;
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} else {
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reg_copy(b, dest);
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if ((tagb == TW_Denormal) && (b->sigh & 0x80000000)) {
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/* A pseudoDenormal, convert it. */
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addexponent(dest, 1);
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tagb = TAG_Valid;
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} else if (tagb > TAG_Empty)
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tagb = TAG_Special;
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setsign(dest, signb); /* signb may differ from the sign of b. */
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FPU_settagi(deststnr, tagb);
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return tagb;
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}
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} else if (tagb == TAG_Zero) {
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reg_copy(a, dest);
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if ((taga == TW_Denormal) && (a->sigh & 0x80000000)) {
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/* A pseudoDenormal */
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addexponent(dest, 1);
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taga = TAG_Valid;
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} else if (taga > TAG_Empty)
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taga = TAG_Special;
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setsign(dest, signa); /* signa may differ from the sign of a. */
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FPU_settagi(deststnr, taga);
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return taga;
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} else if (taga == TW_Infinity) {
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if ((tagb != TW_Infinity) || (signa == signb)) {
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FPU_copy_to_regi(a, TAG_Special, deststnr);
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setsign(dest, signa); /* signa may differ from the sign of a. */
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return taga;
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}
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/* Infinity-Infinity is undefined. */
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return arith_invalid(deststnr);
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} else if (tagb == TW_Infinity) {
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FPU_copy_to_regi(b, TAG_Special, deststnr);
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setsign(dest, signb); /* signb may differ from the sign of b. */
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return tagb;
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}
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#ifdef PARANOID
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EXCEPTION(EX_INTERNAL | 0x101);
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#endif
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return FPU_Exception;
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}
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