1 /* $NetBSD: fpu_add.c,v 1.3 1999/05/30 20:17:48 briggs 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/types.h> 54 #include <sys/systm.h> 55 56 #include <machine/reg.h> 57 58 #include "fpu_arith.h" 59 #include "fpu_emulate.h" 60 61 struct fpn * 62 fpu_add(fe) 63 register struct fpemu *fe; 64 { 65 register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 66 register u_int r0, r1, r2; 67 register int rd; 68 69 /* 70 * Put the `heavier' operand on the right (see fpu_emu.h). 71 * Then we will have one of the following cases, taken in the 72 * following order: 73 * 74 * - y = NaN. Implied: if only one is a signalling NaN, y is. 75 * The result is y. 76 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN 77 * case was taken care of earlier). 78 * If x = -y, the result is NaN. Otherwise the result 79 * is y (an Inf of whichever sign). 80 * - y is 0. Implied: x = 0. 81 * If x and y differ in sign (one positive, one negative), 82 * the result is +0 except when rounding to -Inf. If same: 83 * +0 + +0 = +0; -0 + -0 = -0. 84 * - x is 0. Implied: y != 0. 85 * Result is y. 86 * - other. Implied: both x and y are numbers. 87 * Do addition a la Hennessey & Patterson. 88 */ 89 ORDER(x, y); 90 if (ISNAN(y)) 91 return (y); 92 if (ISINF(y)) { 93 if (ISINF(x) && x->fp_sign != y->fp_sign) 94 return (fpu_newnan(fe)); 95 return (y); 96 } 97 rd = (fe->fe_fpcr & FPCR_ROUND); 98 if (ISZERO(y)) { 99 if (rd != FPCR_MINF) /* only -0 + -0 gives -0 */ 100 y->fp_sign &= x->fp_sign; 101 else /* any -0 operand gives -0 */ 102 y->fp_sign |= x->fp_sign; 103 return (y); 104 } 105 if (ISZERO(x)) 106 return (y); 107 /* 108 * We really have two numbers to add, although their signs may 109 * differ. Make the exponents match, by shifting the smaller 110 * number right (e.g., 1.011 => 0.1011) and increasing its 111 * exponent (2^3 => 2^4). Note that we do not alter the exponents 112 * of x and y here. 113 */ 114 r = &fe->fe_f3; 115 r->fp_class = FPC_NUM; 116 if (x->fp_exp == y->fp_exp) { 117 r->fp_exp = x->fp_exp; 118 r->fp_sticky = 0; 119 } else { 120 if (x->fp_exp < y->fp_exp) { 121 /* 122 * Try to avoid subtract case iii (see below). 123 * This also guarantees that x->fp_sticky = 0. 124 */ 125 SWAP(x, y); 126 } 127 /* now x->fp_exp > y->fp_exp */ 128 r->fp_exp = x->fp_exp; 129 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 130 } 131 r->fp_sign = x->fp_sign; 132 if (x->fp_sign == y->fp_sign) { 133 FPU_DECL_CARRY 134 135 /* 136 * The signs match, so we simply add the numbers. The result 137 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 138 * 11.111...0). If so, a single bit shift-right will fix it 139 * (but remember to adjust the exponent). 140 */ 141 /* r->fp_mant = x->fp_mant + y->fp_mant */ 142 FPU_ADDS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]); 143 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]); 144 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]); 145 if ((r->fp_mant[0] = r0) >= FP_2) { 146 (void) fpu_shr(r, 1); 147 r->fp_exp++; 148 } 149 } else { 150 FPU_DECL_CARRY 151 152 /* 153 * The signs differ, so things are rather more difficult. 154 * H&P would have us negate the negative operand and add; 155 * this is the same as subtracting the negative operand. 156 * This is quite a headache. Instead, we will subtract 157 * y from x, regardless of whether y itself is the negative 158 * operand. When this is done one of three conditions will 159 * hold, depending on the magnitudes of x and y: 160 * case i) |x| > |y|. The result is just x - y, 161 * with x's sign, but it may need to be normalized. 162 * case ii) |x| = |y|. The result is 0 (maybe -0) 163 * so must be fixed up. 164 * case iii) |x| < |y|. We goofed; the result should 165 * be (y - x), with the same sign as y. 166 * We could compare |x| and |y| here and avoid case iii, 167 * but that would take just as much work as the subtract. 168 * We can tell case iii has occurred by an overflow. 169 * 170 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0. 171 */ 172 /* r->fp_mant = x->fp_mant - y->fp_mant */ 173 FPU_SET_CARRY(y->fp_sticky); 174 FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]); 175 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]); 176 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]); 177 if (r0 < FP_2) { 178 /* cases i and ii */ 179 if ((r0 | r1 | r2) == 0) { 180 /* case ii */ 181 r->fp_class = FPC_ZERO; 182 r->fp_sign = (rd == FPCR_MINF); 183 return (r); 184 } 185 } else { 186 /* 187 * Oops, case iii. This can only occur when the 188 * exponents were equal, in which case neither 189 * x nor y have sticky bits set. Flip the sign 190 * (to y's sign) and negate the result to get y - x. 191 */ 192 #ifdef DIAGNOSTIC 193 if (x->fp_exp != y->fp_exp || r->fp_sticky) 194 panic("fpu_add"); 195 #endif 196 r->fp_sign = y->fp_sign; 197 FPU_SUBS(r2, 0, r2); 198 FPU_SUBCS(r1, 0, r1); 199 FPU_SUBC(r0, 0, r0); 200 } 201 r->fp_mant[2] = r2; 202 r->fp_mant[1] = r1; 203 r->fp_mant[0] = r0; 204 if (r0 < FP_1) 205 fpu_norm(r); 206 } 207 return (r); 208 } 209