212 lines
7.1 KiB
C
212 lines
7.1 KiB
C
/* $NetBSD: fpu_add.c,v 1.1 1995/11/03 04:46:58 briggs Exp $ */
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/*
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* Copyright (c) 1992, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This software was developed by the Computer Systems Engineering group
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* at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
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* contributed to Berkeley.
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*
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* All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Lawrence Berkeley Laboratory.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)fpu_add.c 8.1 (Berkeley) 6/11/93
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*/
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/*
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* Perform an FPU add (return x + y).
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*
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* To subtract, negate y and call add.
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*/
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#include <sys/types.h>
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#include <machine/reg.h>
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#include "fpu_arith.h"
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#include "fpu_emulate.h"
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struct fpn *
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fpu_add(fe)
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register struct fpemu *fe;
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{
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register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r;
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register u_int r0, r1, r2, r3;
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register int rd;
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/*
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* Put the `heavier' operand on the right (see fpu_emu.h).
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* Then we will have one of the following cases, taken in the
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* following order:
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*
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* - y = NaN. Implied: if only one is a signalling NaN, y is.
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* The result is y.
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* - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN
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* case was taken care of earlier).
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* If x = -y, the result is NaN. Otherwise the result
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* is y (an Inf of whichever sign).
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* - y is 0. Implied: x = 0.
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* If x and y differ in sign (one positive, one negative),
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* the result is +0 except when rounding to -Inf. If same:
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* +0 + +0 = +0; -0 + -0 = -0.
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* - x is 0. Implied: y != 0.
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* Result is y.
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* - other. Implied: both x and y are numbers.
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* Do addition a la Hennessey & Patterson.
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*/
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ORDER(x, y);
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if (ISNAN(y))
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return (y);
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if (ISINF(y)) {
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if (ISINF(x) && x->fp_sign != y->fp_sign)
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return (fpu_newnan(fe));
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return (y);
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}
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rd = (fe->fe_fpcr & FPCR_ROUND);
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if (ISZERO(y)) {
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if (rd != FPCR_MINF) /* only -0 + -0 gives -0 */
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y->fp_sign &= x->fp_sign;
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else /* any -0 operand gives -0 */
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y->fp_sign |= x->fp_sign;
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return (y);
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}
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if (ISZERO(x))
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return (y);
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/*
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* We really have two numbers to add, although their signs may
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* differ. Make the exponents match, by shifting the smaller
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* number right (e.g., 1.011 => 0.1011) and increasing its
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* exponent (2^3 => 2^4). Note that we do not alter the exponents
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* of x and y here.
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*/
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r = &fe->fe_f3;
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r->fp_class = FPC_NUM;
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if (x->fp_exp == y->fp_exp) {
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r->fp_exp = x->fp_exp;
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r->fp_sticky = 0;
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} else {
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if (x->fp_exp < y->fp_exp) {
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/*
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* Try to avoid subtract case iii (see below).
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* This also guarantees that x->fp_sticky = 0.
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*/
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SWAP(x, y);
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}
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/* now x->fp_exp > y->fp_exp */
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r->fp_exp = x->fp_exp;
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r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp);
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}
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r->fp_sign = x->fp_sign;
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if (x->fp_sign == y->fp_sign) {
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FPU_DECL_CARRY
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/*
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* The signs match, so we simply add the numbers. The result
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* may be `supernormal' (as big as 1.111...1 + 1.111...1, or
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* 11.111...0). If so, a single bit shift-right will fix it
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* (but remember to adjust the exponent).
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*/
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/* r->fp_mant = x->fp_mant + y->fp_mant */
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FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]);
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FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]);
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FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]);
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FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]);
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if ((r->fp_mant[0] = r0) >= FP_2) {
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(void) fpu_shr(r, 1);
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r->fp_exp++;
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}
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} else {
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FPU_DECL_CARRY
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/*
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* The signs differ, so things are rather more difficult.
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* H&P would have us negate the negative operand and add;
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* this is the same as subtracting the negative operand.
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* This is quite a headache. Instead, we will subtract
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* y from x, regardless of whether y itself is the negative
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* operand. When this is done one of three conditions will
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* hold, depending on the magnitudes of x and y:
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* case i) |x| > |y|. The result is just x - y,
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* with x's sign, but it may need to be normalized.
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* case ii) |x| = |y|. The result is 0 (maybe -0)
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* so must be fixed up.
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* case iii) |x| < |y|. We goofed; the result should
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* be (y - x), with the same sign as y.
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* We could compare |x| and |y| here and avoid case iii,
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* but that would take just as much work as the subtract.
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* We can tell case iii has occurred by an overflow.
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*
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* N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0.
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*/
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/* r->fp_mant = x->fp_mant - y->fp_mant */
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FPU_SET_CARRY(y->fp_sticky);
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FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]);
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FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]);
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FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]);
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FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]);
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if (r0 < FP_2) {
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/* cases i and ii */
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if ((r0 | r1 | r2 | r3) == 0) {
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/* case ii */
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r->fp_class = FPC_ZERO;
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r->fp_sign = (rd == FPCR_MINF);
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return (r);
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}
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} else {
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/*
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* Oops, case iii. This can only occur when the
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* exponents were equal, in which case neither
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* x nor y have sticky bits set. Flip the sign
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* (to y's sign) and negate the result to get y - x.
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*/
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#ifdef DIAGNOSTIC
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if (x->fp_exp != y->fp_exp || r->fp_sticky)
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panic("fpu_add");
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#endif
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r->fp_sign = y->fp_sign;
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FPU_SUBS(r3, 0, r3);
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FPU_SUBCS(r2, 0, r2);
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FPU_SUBCS(r1, 0, r1);
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FPU_SUBC(r0, 0, r0);
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}
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r->fp_mant[3] = r3;
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r->fp_mant[2] = r2;
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r->fp_mant[1] = r1;
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r->fp_mant[0] = r0;
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if (r0 < FP_1)
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fpu_norm(r);
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}
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return (r);
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}
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