1 /* $OpenBSD: fpu_add.c,v 1.2 2003/06/02 23:27:55 millert Exp $ */ 2 /* $NetBSD: fpu_add.c,v 1.3 1996/03/14 19:41:52 christos Exp $ */ 3 4 /* 5 * Copyright (c) 1992, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * This software was developed by the Computer Systems Engineering group 9 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and 10 * contributed to Berkeley. 11 * 12 * All advertising materials mentioning features or use of this software 13 * must display the following acknowledgement: 14 * This product includes software developed by the University of 15 * California, Lawrence Berkeley Laboratory. 16 * 17 * Redistribution and use in source and binary forms, with or without 18 * modification, are permitted provided that the following conditions 19 * are met: 20 * 1. Redistributions of source code must retain the above copyright 21 * notice, this list of conditions and the following disclaimer. 22 * 2. Redistributions in binary form must reproduce the above copyright 23 * notice, this list of conditions and the following disclaimer in the 24 * documentation and/or other materials provided with the distribution. 25 * 3. Neither the name of the University nor the names of its contributors 26 * may be used to endorse or promote products derived from this software 27 * without specific prior written permission. 28 * 29 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 30 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 32 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 33 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 37 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 38 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 39 * SUCH DAMAGE. 40 * 41 * @(#)fpu_add.c 8.1 (Berkeley) 6/11/93 42 */ 43 44 /* 45 * Perform an FPU add (return x + y). 46 * 47 * To subtract, negate y and call add. 48 */ 49 50 #include <sys/types.h> 51 #ifdef DIAGNOSTIC 52 #include <sys/systm.h> 53 #endif 54 55 #include <machine/reg.h> 56 #include <machine/instr.h> 57 58 #include <sparc64/fpu/fpu_arith.h> 59 #include <sparc64/fpu/fpu_emu.h> 60 #include <sparc64/fpu/fpu_extern.h> 61 62 struct fpn * 63 fpu_add(fe) 64 register struct fpemu *fe; 65 { 66 register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 67 register u_int r0, r1, r2, r3; 68 register int rd; 69 70 /* 71 * Put the `heavier' operand on the right (see fpu_emu.h). 72 * Then we will have one of the following cases, taken in the 73 * following order: 74 * 75 * - y = NaN. Implied: if only one is a signalling NaN, y is. 76 * The result is y. 77 * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN 78 * case was taken care of earlier). 79 * If x = -y, the result is NaN. Otherwise the result 80 * is y (an Inf of whichever sign). 81 * - y is 0. Implied: x = 0. 82 * If x and y differ in sign (one positive, one negative), 83 * the result is +0 except when rounding to -Inf. If same: 84 * +0 + +0 = +0; -0 + -0 = -0. 85 * - x is 0. Implied: y != 0. 86 * Result is y. 87 * - other. Implied: both x and y are numbers. 88 * Do addition a la Hennessey & Patterson. 89 */ 90 ORDER(x, y); 91 if (ISNAN(y)) 92 return (y); 93 if (ISINF(y)) { 94 if (ISINF(x) && x->fp_sign != y->fp_sign) 95 return (fpu_newnan(fe)); 96 return (y); 97 } 98 rd = ((fe->fe_fsr >> FSR_RD_SHIFT) & FSR_RD_MASK); 99 if (ISZERO(y)) { 100 if (rd != FSR_RD_RM) /* only -0 + -0 gives -0 */ 101 y->fp_sign &= x->fp_sign; 102 else /* any -0 operand gives -0 */ 103 y->fp_sign |= x->fp_sign; 104 return (y); 105 } 106 if (ISZERO(x)) 107 return (y); 108 /* 109 * We really have two numbers to add, although their signs may 110 * differ. Make the exponents match, by shifting the smaller 111 * number right (e.g., 1.011 => 0.1011) and increasing its 112 * exponent (2^3 => 2^4). Note that we do not alter the exponents 113 * of x and y here. 114 */ 115 r = &fe->fe_f3; 116 r->fp_class = FPC_NUM; 117 if (x->fp_exp == y->fp_exp) { 118 r->fp_exp = x->fp_exp; 119 r->fp_sticky = 0; 120 } else { 121 if (x->fp_exp < y->fp_exp) { 122 /* 123 * Try to avoid subtract case iii (see below). 124 * This also guarantees that x->fp_sticky = 0. 125 */ 126 SWAP(x, y); 127 } 128 /* now x->fp_exp > y->fp_exp */ 129 r->fp_exp = x->fp_exp; 130 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 131 } 132 r->fp_sign = x->fp_sign; 133 if (x->fp_sign == y->fp_sign) { 134 FPU_DECL_CARRY 135 136 /* 137 * The signs match, so we simply add the numbers. The result 138 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 139 * 11.111...0). If so, a single bit shift-right will fix it 140 * (but remember to adjust the exponent). 141 */ 142 /* r->fp_mant = x->fp_mant + y->fp_mant */ 143 FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]); 144 FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]); 145 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]); 146 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]); 147 if ((r->fp_mant[0] = r0) >= FP_2) { 148 (void) fpu_shr(r, 1); 149 r->fp_exp++; 150 } 151 } else { 152 FPU_DECL_CARRY 153 154 /* 155 * The signs differ, so things are rather more difficult. 156 * H&P would have us negate the negative operand and add; 157 * this is the same as subtracting the negative operand. 158 * This is quite a headache. Instead, we will subtract 159 * y from x, regardless of whether y itself is the negative 160 * operand. When this is done one of three conditions will 161 * hold, depending on the magnitudes of x and y: 162 * case i) |x| > |y|. The result is just x - y, 163 * with x's sign, but it may need to be normalized. 164 * case ii) |x| = |y|. The result is 0 (maybe -0) 165 * so must be fixed up. 166 * case iii) |x| < |y|. We goofed; the result should 167 * be (y - x), with the same sign as y. 168 * We could compare |x| and |y| here and avoid case iii, 169 * but that would take just as much work as the subtract. 170 * We can tell case iii has occurred by an overflow. 171 * 172 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0. 173 */ 174 /* r->fp_mant = x->fp_mant - y->fp_mant */ 175 FPU_SET_CARRY(y->fp_sticky); 176 FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]); 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 | r3) == 0) { 183 /* case ii */ 184 r->fp_class = FPC_ZERO; 185 r->fp_sign = rd == FSR_RD_RM; 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(r3, 0, r3); 201 FPU_SUBCS(r2, 0, r2); 202 FPU_SUBCS(r1, 0, r1); 203 FPU_SUBC(r0, 0, r0); 204 } 205 r->fp_mant[3] = r3; 206 r->fp_mant[2] = r2; 207 r->fp_mant[1] = r1; 208 r->fp_mant[0] = r0; 209 if (r0 < FP_1) 210 fpu_norm(r); 211 } 212 return (r); 213 } 214