1/* $NetBSD: fpu_add.c,v 1.5 2003/08/07 16:29:36 agc Exp $ */ 2 3/* 4 * Copyright (c) 1992, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This software was developed by the Computer Systems Engineering group 8 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 9 * contributed to Berkeley. 10 * 11 * All advertising materials mentioning features or use of this software 12 * must display the following acknowledgement: 13 * This product includes software developed by the University of 14 * California, Lawrence Berkeley Laboratory. 15 * 16 * Redistribution and use in source and binary forms, with or without 17 * modification, are permitted provided that the following conditions 18 * are met: 19 * 1. Redistributions of source code must retain the above copyright 20 * notice, this list of conditions and the following disclaimer. 21 * 2. Redistributions in binary form must reproduce the above copyright 22 * notice, this list of conditions and the following disclaimer in the 23 * documentation and/or other materials provided with the distribution. 24 * 3. Neither the name of the University nor the names of its contributors 25 * may be used to endorse or promote products derived from this software 26 * without specific prior written permission. 27 * 28 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 29 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 30 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 31 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 32 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 33 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 34 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 35 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 36 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 37 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 38 * SUCH DAMAGE. 39 * 40 * @(#)fpu_add.c 8.1 (Berkeley) 6/11/93 41 */ 42 43/* 44 * Perform an FPU add (return x + y). 45 * 46 * To subtract, negate y and call add. 47 */ 48 49#include <sys/cdefs.h> 50__KERNEL_RCSID(0, "$NetBSD: fpu_add.c,v 1.5 2003/08/07 16:29:36 agc Exp $"); 51 52#include <sys/types.h> 53#ifdef DIAGNOSTIC 54#include <sys/systm.h> 55#endif 56 57#include <machine/reg.h> 58#include <machine/instr.h> 59 60#include <sparc/fpu/fpu_arith.h> 61#include <sparc/fpu/fpu_emu.h> 62#include <sparc/fpu/fpu_extern.h> 63 64struct fpn * 65fpu_add(struct fpemu *fe) 66{ 67 register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 68 register u_int r0, r1, r2, r3; 69 register int rd; 70 71 /* 72 * Put the `heavier' operand on the right (see fpu_emu.h). 73 * Then we will have one of the following cases, taken in the 74 * following order: 75 * 76 * - y = NaN. Implied: if only one is a signalling NaN, y is. 77 * The result is y. 78 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN 79 * case was taken care of earlier). 80 * If x = -y, the result is NaN. Otherwise the result 81 * is y (an Inf of whichever sign). 82 * - y is 0. Implied: x = 0. 83 * If x and y differ in sign (one positive, one negative), 84 * the result is +0 except when rounding to -Inf. If same: 85 * +0 + +0 = +0; -0 + -0 = -0. 86 * - x is 0. Implied: y != 0. 87 * Result is y. 88 * - other. Implied: both x and y are numbers. 89 * Do addition a la Hennessey & Patterson. 90 */ 91 ORDER(x, y); 92 if (ISNAN(y)) 93 return (y); 94 if (ISINF(y)) { 95 if (ISINF(x) && x->fp_sign != y->fp_sign) 96 return (fpu_newnan(fe)); 97 return (y); 98 } 99 rd = ((fe->fe_fsr >> FSR_RD_SHIFT) & FSR_RD_MASK); 100 if (ISZERO(y)) { 101 if (rd != FSR_RD_RM) /* only -0 + -0 gives -0 */ 102 y->fp_sign &= x->fp_sign; 103 else /* any -0 operand gives -0 */ 104 y->fp_sign |= x->fp_sign; 105 return (y); 106 } 107 if (ISZERO(x)) 108 return (y); 109 /* 110 * We really have two numbers to add, although their signs may 111 * differ. Make the exponents match, by shifting the smaller 112 * number right (e.g., 1.011 => 0.1011) and increasing its 113 * exponent (2^3 => 2^4). Note that we do not alter the exponents 114 * of x and y here. 115 */ 116 r = &fe->fe_f3; 117 r->fp_class = FPC_NUM; 118 if (x->fp_exp == y->fp_exp) { 119 r->fp_exp = x->fp_exp; 120 r->fp_sticky = 0; 121 } else { 122 if (x->fp_exp < y->fp_exp) { 123 /* 124 * Try to avoid subtract case iii (see below). 125 * This also guarantees that x->fp_sticky = 0. 126 */ 127 SWAP(x, y); 128 } 129 /* now x->fp_exp > y->fp_exp */ 130 r->fp_exp = x->fp_exp; 131 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 132 } 133 r->fp_sign = x->fp_sign; 134 if (x->fp_sign == y->fp_sign) { 135 FPU_DECL_CARRY 136 137 /* 138 * The signs match, so we simply add the numbers. The result 139 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 140 * 11.111...0). If so, a single bit shift-right will fix it 141 * (but remember to adjust the exponent). 142 */ 143 /* r->fp_mant = x->fp_mant + y->fp_mant */ 144 FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]); 145 FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]); 146 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]); 147 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]); 148 if ((r->fp_mant[0] = r0) >= FP_2) { 149 (void) fpu_shr(r, 1); 150 r->fp_exp++; 151 } 152 } else { 153 FPU_DECL_CARRY 154 155 /* 156 * The signs differ, so things are rather more difficult. 157 * H&P would have us negate the negative operand and add; 158 * this is the same as subtracting the negative operand. 159 * This is quite a headache. Instead, we will subtract 160 * y from x, regardless of whether y itself is the negative 161 * operand. When this is done one of three conditions will 162 * hold, depending on the magnitudes of x and y: 163 * case i) |x| > |y|. The result is just x - y, 164 * with x's sign, but it may need to be normalized. 165 * case ii) |x| = |y|. The result is 0 (maybe -0) 166 * so must be fixed up. 167 * case iii) |x| < |y|. We goofed; the result should 168 * be (y - x), with the same sign as y. 169 * We could compare |x| and |y| here and avoid case iii, 170 * but that would take just as much work as the subtract. 171 * We can tell case iii has occurred by an overflow. 172 * 173 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0. 174 */ 175 /* r->fp_mant = x->fp_mant - y->fp_mant */ 176 FPU_SET_CARRY(y->fp_sticky); 177 FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]); 178 FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]); 179 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]); 180 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]); 181 if (r0 < FP_2) { 182 /* cases i and ii */ 183 if ((r0 | r1 | r2 | r3) == 0) { 184 /* case ii */ 185 r->fp_class = FPC_ZERO; 186 r->fp_sign = rd == FSR_RD_RM; 187 return (r); 188 } 189 } else { 190 /* 191 * Oops, case iii. This can only occur when the 192 * exponents were equal, in which case neither 193 * x nor y have sticky bits set. Flip the sign 194 * (to y's sign) and negate the result to get y - x. 195 */ 196#ifdef DIAGNOSTIC 197 if (x->fp_exp != y->fp_exp || r->fp_sticky) 198 panic("fpu_add"); 199#endif 200 r->fp_sign = y->fp_sign; 201 FPU_SUBS(r3, 0, r3); 202 FPU_SUBCS(r2, 0, r2); 203 FPU_SUBCS(r1, 0, r1); 204 FPU_SUBC(r0, 0, r0); 205 } 206 r->fp_mant[3] = r3; 207 r->fp_mant[2] = r2; 208 r->fp_mant[1] = r1; 209 r->fp_mant[0] = r0; 210 if (r0 < FP_1) 211 fpu_norm(r); 212 } 213 return (r); 214} 215