/* $NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $ */ /* * Copyright (c) 1995 Ken Nakata * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the author nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)fpu_rem.c 10/24/95 */ #include <sys/cdefs.h> __KERNEL_RCSID(0, "$NetBSD: fpu_rem.c,v 1.18 2023/11/19 03:58:15 isaki Exp $"); #include <sys/types.h> #include <sys/signal.h> #include <machine/frame.h> #include "fpu_emulate.h" /* * ALGORITHM * * Step 1. Save and strip signs of X and Y: signX := sign(X), * signY := sign(Y), X := *X*, Y := *Y*, * signQ := signX EOR signY. Record whether MOD or REM * is requested. * * Step 2. Set L := expo(X)-expo(Y), Q := 0. * If (L < 0) then * R := X, go to Step 4. * else * R := 2^(-L)X, j := L. * endif * * Step 3. Perform MOD(X,Y) * 3.1 If R = Y, then { Q := Q + 1, R := 0, go to Step 7. } * 3.2 If R > Y, then { R := R - Y, Q := Q + 1} * 3.3 If j = 0, go to Step 4. * 3.4 j := j - 1, Q := 2Q, R := 2R. Go to Step 3.1. * * Step 4. R := signX*R. * * Step 5. If MOD is requested, go to Step 7. * * Step 6. Now, R = MOD(X,Y), convert to REM(X,Y) is requested. * Do banker's rounding. * If abs(R) > Y/2 * || (abs(R) == Y/2 && Q % 2 == 1) then * { Q := Q + 1, R := R - signX * Y }. * * Step 7. Return signQ, last 7 bits of Q, and R as required. */ static struct fpn * __fpu_modrem(struct fpemu *fe, int is_mod); static int abscmp3(const struct fpn *a, const struct fpn *b); /* Absolute FORTRAN Compare */ static int abscmp3(const struct fpn *a, const struct fpn *b) { int i; if (a->fp_exp < b->fp_exp) { return -1; } else if (a->fp_exp > b->fp_exp) { return 1; } else { for (i = 0; i < 3; i++) { if (a->fp_mant[i] < b->fp_mant[i]) return -1; else if (a->fp_mant[i] > b->fp_mant[i]) return 1; } } return 0; } static struct fpn * __fpu_modrem(struct fpemu *fe, int is_mod) { static struct fpn X, Y; struct fpn *x, *y, *r; uint32_t signX, signY, signQ; int j, l, q; int cmp; if (ISNAN(&fe->fe_f1) || ISNAN(&fe->fe_f2)) return fpu_newnan(fe); if (ISINF(&fe->fe_f1) || ISZERO(&fe->fe_f2)) return fpu_newnan(fe); CPYFPN(&X, &fe->fe_f1); CPYFPN(&Y, &fe->fe_f2); x = &X; y = &Y; q = 0; r = &fe->fe_f2; /* * Step 1 */ signX = x->fp_sign; signY = y->fp_sign; signQ = (signX ^ signY); x->fp_sign = y->fp_sign = 0; /* Special treatment that just return input value but Q is necessary */ if (ISZERO(x) || ISINF(y)) { r = &fe->fe_f1; goto Step7; } /* * Step 2 */ l = x->fp_exp - y->fp_exp; CPYFPN(r, x); if (l >= 0) { r->fp_exp -= l; j = l; /* * Step 3 */ for (;;) { cmp = abscmp3(r, y); /* Step 3.1 */ if (cmp == 0) break; /* Step 3.2 */ if (cmp > 0) { CPYFPN(&fe->fe_f1, r); CPYFPN(&fe->fe_f2, y); fe->fe_f2.fp_sign = 1; r = fpu_add(fe); q++; } /* Step 3.3 */ if (j == 0) goto Step4; /* Step 3.4 */ j--; q += q; r->fp_exp++; } /* R == Y */ q++; r->fp_class = FPC_ZERO; goto Step7; } Step4: r->fp_sign = signX; /* * Step 5 */ if (is_mod) goto Step7; /* * Step 6 */ /* y = y / 2 */ y->fp_exp--; /* abscmp3 ignore sign */ cmp = abscmp3(r, y); /* revert y */ y->fp_exp++; if (cmp > 0 || (cmp == 0 && q % 2)) { q++; CPYFPN(&fe->fe_f1, r); CPYFPN(&fe->fe_f2, y); fe->fe_f2.fp_sign = !signX; r = fpu_add(fe); } /* * Step 7 */ Step7: q &= 0x7f; q |= (signQ << 7); fe->fe_fpframe->fpf_fpsr = fe->fe_fpsr = (fe->fe_fpsr & ~FPSR_QTT) | (q << 16); return r; } struct fpn * fpu_rem(struct fpemu *fe) { return __fpu_modrem(fe, 0); } struct fpn * fpu_mod(struct fpemu *fe) { return __fpu_modrem(fe, 1); }
