1 /* $NetBSD: fpu_add.c,v 1.3 1996/03/14 19:41:52 christos 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 #ifdef DIAGNOSTIC 55 #include <sys/systm.h> 56 #endif 57 58 #include <machine/reg.h> 59 #include <machine/instr.h> 60 61 #include <sparc/fpu/fpu_arith.h> 62 #include <sparc/fpu/fpu_emu.h> 63 #include <sparc/fpu/fpu_extern.h> 64 65 struct fpn * 66 fpu_add(fe) 67 register struct fpemu *fe; 68 { 69 register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 70 register u_int r0, r1, r2, r3; 71 register int rd; 72 73 /* 74 * Put the `heavier' operand on the right (see fpu_emu.h). 75 * Then we will have one of the following cases, taken in the 76 * following order: 77 * 78 * - y = NaN. Implied: if only one is a signalling NaN, y is. 79 * The result is y. 80 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN 81 * case was taken care of earlier). 82 * If x = -y, the result is NaN. Otherwise the result 83 * is y (an Inf of whichever sign). 84 * - y is 0. Implied: x = 0. 85 * If x and y differ in sign (one positive, one negative), 86 * the result is +0 except when rounding to -Inf. If same: 87 * +0 + +0 = +0; -0 + -0 = -0. 88 * - x is 0. Implied: y != 0. 89 * Result is y. 90 * - other. Implied: both x and y are numbers. 91 * Do addition a la Hennessey & Patterson. 92 */ 93 ORDER(x, y); 94 if (ISNAN(y)) 95 return (y); 96 if (ISINF(y)) { 97 if (ISINF(x) && x->fp_sign != y->fp_sign) 98 return (fpu_newnan(fe)); 99 return (y); 100 } 101 rd = ((fe->fe_fsr >> FSR_RD_SHIFT) & FSR_RD_MASK); 102 if (ISZERO(y)) { 103 if (rd != FSR_RD_RM) /* only -0 + -0 gives -0 */ 104 y->fp_sign &= x->fp_sign; 105 else /* any -0 operand gives -0 */ 106 y->fp_sign |= x->fp_sign; 107 return (y); 108 } 109 if (ISZERO(x)) 110 return (y); 111 /* 112 * We really have two numbers to add, although their signs may 113 * differ. Make the exponents match, by shifting the smaller 114 * number right (e.g., 1.011 => 0.1011) and increasing its 115 * exponent (2^3 => 2^4). Note that we do not alter the exponents 116 * of x and y here. 117 */ 118 r = &fe->fe_f3; 119 r->fp_class = FPC_NUM; 120 if (x->fp_exp == y->fp_exp) { 121 r->fp_exp = x->fp_exp; 122 r->fp_sticky = 0; 123 } else { 124 if (x->fp_exp < y->fp_exp) { 125 /* 126 * Try to avoid subtract case iii (see below). 127 * This also guarantees that x->fp_sticky = 0. 128 */ 129 SWAP(x, y); 130 } 131 /* now x->fp_exp > y->fp_exp */ 132 r->fp_exp = x->fp_exp; 133 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 134 } 135 r->fp_sign = x->fp_sign; 136 if (x->fp_sign == y->fp_sign) { 137 FPU_DECL_CARRY 138 139 /* 140 * The signs match, so we simply add the numbers. The result 141 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 142 * 11.111...0). If so, a single bit shift-right will fix it 143 * (but remember to adjust the exponent). 144 */ 145 /* r->fp_mant = x->fp_mant + y->fp_mant */ 146 FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]); 147 FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]); 148 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]); 149 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]); 150 if ((r->fp_mant[0] = r0) >= FP_2) { 151 (void) fpu_shr(r, 1); 152 r->fp_exp++; 153 } 154 } else { 155 FPU_DECL_CARRY 156 157 /* 158 * The signs differ, so things are rather more difficult. 159 * H&P would have us negate the negative operand and add; 160 * this is the same as subtracting the negative operand. 161 * This is quite a headache. Instead, we will subtract 162 * y from x, regardless of whether y itself is the negative 163 * operand. When this is done one of three conditions will 164 * hold, depending on the magnitudes of x and y: 165 * case i) |x| > |y|. The result is just x - y, 166 * with x's sign, but it may need to be normalized. 167 * case ii) |x| = |y|. The result is 0 (maybe -0) 168 * so must be fixed up. 169 * case iii) |x| < |y|. We goofed; the result should 170 * be (y - x), with the same sign as y. 171 * We could compare |x| and |y| here and avoid case iii, 172 * but that would take just as much work as the subtract. 173 * We can tell case iii has occurred by an overflow. 174 * 175 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0. 176 */ 177 /* r->fp_mant = x->fp_mant - y->fp_mant */ 178 FPU_SET_CARRY(y->fp_sticky); 179 FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]); 180 FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]); 181 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]); 182 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]); 183 if (r0 < FP_2) { 184 /* cases i and ii */ 185 if ((r0 | r1 | r2 | r3) == 0) { 186 /* case ii */ 187 r->fp_class = FPC_ZERO; 188 r->fp_sign = rd == FSR_RD_RM; 189 return (r); 190 } 191 } else { 192 /* 193 * Oops, case iii. This can only occur when the 194 * exponents were equal, in which case neither 195 * x nor y have sticky bits set. Flip the sign 196 * (to y's sign) and negate the result to get y - x. 197 */ 198 #ifdef DIAGNOSTIC 199 if (x->fp_exp != y->fp_exp || r->fp_sticky) 200 panic("fpu_add"); 201 #endif 202 r->fp_sign = y->fp_sign; 203 FPU_SUBS(r3, 0, r3); 204 FPU_SUBCS(r2, 0, r2); 205 FPU_SUBCS(r1, 0, r1); 206 FPU_SUBC(r0, 0, r0); 207 } 208 r->fp_mant[3] = r3; 209 r->fp_mant[2] = r2; 210 r->fp_mant[1] = r1; 211 r->fp_mant[0] = r0; 212 if (r0 < FP_1) 213 fpu_norm(r); 214 } 215 return (r); 216 } 217