235 lines
6.1 KiB
C
235 lines
6.1 KiB
C
/* $NetBSD: fpu_rem.c,v 1.6 2005/12/11 12:17:52 christos Exp $ */
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/*
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* Copyright (c) 1995 Ken Nakata
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* All rights reserved.
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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. Neither the name of the author 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 AUTHOR 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 AUTHOR 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_rem.c 10/24/95
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: fpu_rem.c,v 1.6 2005/12/11 12:17:52 christos Exp $");
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#include <sys/types.h>
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#include <sys/signal.h>
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#include <machine/frame.h>
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#include "fpu_emulate.h"
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/*
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* ALGORITHM
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*
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* Step 1. Save and strip signs of X and Y: signX := sign(X),
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* signY := sign(Y), X := *X*, Y := *Y*,
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* signQ := signX EOR signY. Record whether MOD or REM
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* is requested.
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*
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* Step 2. Set L := expo(X)-expo(Y), k := 0, Q := 0.
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* If (L < 0) then
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* R := X, go to Step 4.
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* else
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* R := 2^(-L)X, j := L.
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* endif
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*
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* Step 3. Perform MOD(X,Y)
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* 3.1 If R = Y, go to Step 9.
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* 3.2 If R > Y, then { R := R - Y, Q := Q + 1}
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* 3.3 If j = 0, go to Step 4.
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* 3.4 k := k + 1, j := j - 1, Q := 2Q, R := 2R. Go to
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* Step 3.1.
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*
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* Step 4. At this point, R = X - QY = MOD(X,Y). Set
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* Last_Subtract := false (used in Step 7 below). If
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* MOD is requested, go to Step 6.
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*
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* Step 5. R = MOD(X,Y), but REM(X,Y) is requested.
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* 5.1 If R < Y/2, then R = MOD(X,Y) = REM(X,Y). Go to
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* Step 6.
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* 5.2 If R > Y/2, then { set Last_Subtract := true,
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* Q := Q + 1, Y := signY*Y }. Go to Step 6.
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* 5.3 This is the tricky case of R = Y/2. If Q is odd,
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* then { Q := Q + 1, signX := -signX }.
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*
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* Step 6. R := signX*R.
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*
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* Step 7. If Last_Subtract = true, R := R - Y.
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*
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* Step 8. Return signQ, last 7 bits of Q, and R as required.
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*
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* Step 9. At this point, R = 2^(-j)*X - Q Y = Y. Thus,
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* X = 2^(j)*(Q+1)Y. set Q := 2^(j)*(Q+1),
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* R := 0. Return signQ, last 7 bits of Q, and R.
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*/
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static struct fpn * __fpu_modrem __P((struct fpemu *fe, int modrem));
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static struct fpn *
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__fpu_modrem(fe, modrem)
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struct fpemu *fe;
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int modrem;
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{
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static struct fpn X, Y;
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struct fpn *x, *y, *r;
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u_int signX, signY, signQ;
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int j, k, l, q;
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int Last_Subtract;
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CPYFPN(&X, &fe->fe_f1);
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CPYFPN(&Y, &fe->fe_f2);
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x = &X;
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y = &Y;
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r = &fe->fe_f2;
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/*
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* Step 1
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*/
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signX = x->fp_sign;
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signY = y->fp_sign;
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signQ = (signX ^ signY);
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x->fp_sign = y->fp_sign = 0;
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/*
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* Step 2
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*/
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l = x->fp_exp - y->fp_exp;
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k = 0;
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q = 0;
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if (l >= 0) {
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CPYFPN(r, x);
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r->fp_exp -= l;
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j = l;
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/*
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* Step 3
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*/
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while (y->fp_exp != r->fp_exp || y->fp_mant[0] != r->fp_mant[0] ||
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y->fp_mant[1] != r->fp_mant[1] ||
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y->fp_mant[2] != r->fp_mant[2]) {
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/* Step 3.2 */
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if (y->fp_exp < r->fp_exp || y->fp_mant[0] < r->fp_mant[0] ||
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y->fp_mant[1] < r->fp_mant[1] ||
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y->fp_mant[2] < r->fp_mant[2]) {
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CPYFPN(&fe->fe_f1, r);
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CPYFPN(&fe->fe_f2, y);
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fe->fe_f2.fp_sign = 1;
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r = fpu_add(fe);
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q++;
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}
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/* Step 3.3 */
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if (j == 0)
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goto Step4;
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/* Step 3.4 */
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k++;
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j--;
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q += q;
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r->fp_exp++;
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}
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/* Step 9 */
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goto Step9;
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}
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Step4:
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Last_Subtract = 0;
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if (modrem == 0)
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goto Step6;
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/*
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* Step 5
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*/
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/* Step 5.1 */
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if (r->fp_exp + 1 < y->fp_exp ||
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(r->fp_exp + 1 == y->fp_exp &&
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(r->fp_mant[0] < y->fp_mant[0] || r->fp_mant[1] < y->fp_mant[1] ||
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r->fp_mant[2] < y->fp_mant[2])))
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/* if r < y/2 */
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goto Step6;
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/* Step 5.2 */
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if (r->fp_exp + 1 != y->fp_exp ||
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r->fp_mant[0] != y->fp_mant[0] || r->fp_mant[1] != y->fp_mant[1] ||
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r->fp_mant[2] != y->fp_mant[2]) {
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/* if (!(r < y/2) && !(r == y/2)) */
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Last_Subtract = 1;
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q++;
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y->fp_sign = signY;
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} else {
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/* Step 5.3 */
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/* r == y/2 */
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if (q % 2) {
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q++;
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signX = !signX;
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}
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}
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Step6:
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r->fp_sign = signX;
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/*
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* Step 7
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*/
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if (Last_Subtract) {
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CPYFPN(&fe->fe_f1, r);
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CPYFPN(&fe->fe_f2, y);
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fe->fe_f2.fp_sign = !y->fp_sign;
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r = fpu_add(fe);
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}
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/*
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* Step 8
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*/
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q &= 0x7f;
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q |= (signQ << 7);
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fe->fe_fpframe->fpf_fpsr =
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fe->fe_fpsr =
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(fe->fe_fpsr & ~FPSR_QTT) | (q << 16);
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return r;
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Step9:
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fe->fe_f1.fp_class = FPC_ZERO;
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q++;
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q &= 0x7f;
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q |= (signQ << 7);
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fe->fe_fpframe->fpf_fpsr =
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fe->fe_fpsr =
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(fe->fe_fpsr & ~FPSR_QTT) | (q << 16);
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return &fe->fe_f1;
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}
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struct fpn *
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fpu_rem(fe)
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struct fpemu *fe;
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{
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return __fpu_modrem(fe, 1);
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}
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struct fpn *
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fpu_mod(fe)
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struct fpemu *fe;
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{
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return __fpu_modrem(fe, 0);
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}
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