1 /* $NetBSD: fpu_add.c,v 1.4 2003/07/15 02:43:09 lukem 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. All advertising materials mentioning features or use of this software 25 * must display the following acknowledgement: 26 * This product includes software developed by the University of 27 * California, Berkeley and its contributors. 28 * 4. Neither the name of the University nor the names of its contributors 29 * may be used to endorse or promote products derived from this software 30 * without specific prior written permission. 31 * 32 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 33 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 34 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 35 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 36 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 37 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 38 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 40 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 41 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 42 * SUCH DAMAGE. 43 * 44 * @(#)fpu_add.c 8.1 (Berkeley) 6/11/93 45 */ 46 47 /* 48 * Perform an FPU add (return x + y). 49 * 50 * To subtract, negate y and call add. 51 */ 52 53 #include <sys/cdefs.h> 54 __KERNEL_RCSID(0, "$NetBSD: fpu_add.c,v 1.4 2003/07/15 02:43:09 lukem Exp $"); 55 56 #include <sys/types.h> 57 #include <sys/systm.h> 58 59 #include <machine/reg.h> 60 61 #include "fpu_arith.h" 62 #include "fpu_emulate.h" 63 64 struct fpn * 65 fpu_add(fe) 66 register struct fpemu *fe; 67 { 68 register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 69 register u_int r0, r1, r2; 70 register int rd; 71 72 /* 73 * Put the `heavier' operand on the right (see fpu_emu.h). 74 * Then we will have one of the following cases, taken in the 75 * following order: 76 * 77 * - y = NaN. Implied: if only one is a signalling NaN, y is. 78 * The result is y. 79 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN 80 * case was taken care of earlier). 81 * If x = -y, the result is NaN. Otherwise the result 82 * is y (an Inf of whichever sign). 83 * - y is 0. Implied: x = 0. 84 * If x and y differ in sign (one positive, one negative), 85 * the result is +0 except when rounding to -Inf. If same: 86 * +0 + +0 = +0; -0 + -0 = -0. 87 * - x is 0. Implied: y != 0. 88 * Result is y. 89 * - other. Implied: both x and y are numbers. 90 * Do addition a la Hennessey & Patterson. 91 */ 92 ORDER(x, y); 93 if (ISNAN(y)) 94 return (y); 95 if (ISINF(y)) { 96 if (ISINF(x) && x->fp_sign != y->fp_sign) 97 return (fpu_newnan(fe)); 98 return (y); 99 } 100 rd = (fe->fe_fpcr & FPCR_ROUND); 101 if (ISZERO(y)) { 102 if (rd != FPCR_MINF) /* only -0 + -0 gives -0 */ 103 y->fp_sign &= x->fp_sign; 104 else /* any -0 operand gives -0 */ 105 y->fp_sign |= x->fp_sign; 106 return (y); 107 } 108 if (ISZERO(x)) 109 return (y); 110 /* 111 * We really have two numbers to add, although their signs may 112 * differ. Make the exponents match, by shifting the smaller 113 * number right (e.g., 1.011 => 0.1011) and increasing its 114 * exponent (2^3 => 2^4). Note that we do not alter the exponents 115 * of x and y here. 116 */ 117 r = &fe->fe_f3; 118 r->fp_class = FPC_NUM; 119 if (x->fp_exp == y->fp_exp) { 120 r->fp_exp = x->fp_exp; 121 r->fp_sticky = 0; 122 } else { 123 if (x->fp_exp < y->fp_exp) { 124 /* 125 * Try to avoid subtract case iii (see below). 126 * This also guarantees that x->fp_sticky = 0. 127 */ 128 SWAP(x, y); 129 } 130 /* now x->fp_exp > y->fp_exp */ 131 r->fp_exp = x->fp_exp; 132 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 133 } 134 r->fp_sign = x->fp_sign; 135 if (x->fp_sign == y->fp_sign) { 136 FPU_DECL_CARRY 137 138 /* 139 * The signs match, so we simply add the numbers. The result 140 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 141 * 11.111...0). If so, a single bit shift-right will fix it 142 * (but remember to adjust the exponent). 143 */ 144 /* r->fp_mant = x->fp_mant + y->fp_mant */ 145 FPU_ADDS(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(r2, x->fp_mant[2], y->fp_mant[2]); 178 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]); 179 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]); 180 if (r0 < FP_2) { 181 /* cases i and ii */ 182 if ((r0 | r1 | r2) == 0) { 183 /* case ii */ 184 r->fp_class = FPC_ZERO; 185 r->fp_sign = (rd == FPCR_MINF); 186 return (r); 187 } 188 } else { 189 /* 190 * Oops, case iii. This can only occur when the 191 * exponents were equal, in which case neither 192 * x nor y have sticky bits set. Flip the sign 193 * (to y's sign) and negate the result to get y - x. 194 */ 195 #ifdef DIAGNOSTIC 196 if (x->fp_exp != y->fp_exp || r->fp_sticky) 197 panic("fpu_add"); 198 #endif 199 r->fp_sign = y->fp_sign; 200 FPU_SUBS(r2, 0, r2); 201 FPU_SUBCS(r1, 0, r1); 202 FPU_SUBC(r0, 0, r0); 203 } 204 r->fp_mant[2] = r2; 205 r->fp_mant[1] = r1; 206 r->fp_mant[0] = r0; 207 if (r0 < FP_1) 208 fpu_norm(r); 209 } 210 return (r); 211 } 212