1 /* $NetBSD: fpu_add.c,v 1.4 2005/12/11 12:18:42 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. 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 __FBSDID("$FreeBSD$"); 51 52 #include <sys/types.h> 53 #include <sys/systm.h> 54 55 #include <machine/fpu.h> 56 #include <machine/ieeefp.h> 57 #include <machine/reg.h> 58 59 #include <powerpc/fpu/fpu_arith.h> 60 #include <powerpc/fpu/fpu_emu.h> 61 62 struct fpn * 63 fpu_add(struct fpemu *fe) 64 { 65 struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2, *r; 66 u_int r0, r1, r2, r3; 67 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 DPRINTF(FPE_REG, ("fpu_add:\n")); 90 DUMPFPN(FPE_REG, x); 91 DUMPFPN(FPE_REG, y); 92 DPRINTF(FPE_REG, ("=>\n")); 93 ORDER(x, y); 94 if (ISNAN(y)) { 95 fe->fe_cx |= FPSCR_VXSNAN; 96 DUMPFPN(FPE_REG, y); 97 return (y); 98 } 99 if (ISINF(y)) { 100 if (ISINF(x) && x->fp_sign != y->fp_sign) { 101 fe->fe_cx |= FPSCR_VXISI; 102 return (fpu_newnan(fe)); 103 } 104 DUMPFPN(FPE_REG, y); 105 return (y); 106 } 107 rd = ((fe->fe_fpscr) & FPSCR_RN); 108 if (ISZERO(y)) { 109 if (rd != FP_RM) /* only -0 + -0 gives -0 */ 110 y->fp_sign &= x->fp_sign; 111 else /* any -0 operand gives -0 */ 112 y->fp_sign |= x->fp_sign; 113 DUMPFPN(FPE_REG, y); 114 return (y); 115 } 116 if (ISZERO(x)) { 117 DUMPFPN(FPE_REG, y); 118 return (y); 119 } 120 /* 121 * We really have two numbers to add, although their signs may 122 * differ. Make the exponents match, by shifting the smaller 123 * number right (e.g., 1.011 => 0.1011) and increasing its 124 * exponent (2^3 => 2^4). Note that we do not alter the exponents 125 * of x and y here. 126 */ 127 r = &fe->fe_f3; 128 r->fp_class = FPC_NUM; 129 if (x->fp_exp == y->fp_exp) { 130 r->fp_exp = x->fp_exp; 131 r->fp_sticky = 0; 132 } else { 133 if (x->fp_exp < y->fp_exp) { 134 /* 135 * Try to avoid subtract case iii (see below). 136 * This also guarantees that x->fp_sticky = 0. 137 */ 138 SWAP(x, y); 139 } 140 /* now x->fp_exp > y->fp_exp */ 141 r->fp_exp = x->fp_exp; 142 r->fp_sticky = fpu_shr(y, x->fp_exp - y->fp_exp); 143 } 144 r->fp_sign = x->fp_sign; 145 if (x->fp_sign == y->fp_sign) { 146 FPU_DECL_CARRY 147 148 /* 149 * The signs match, so we simply add the numbers. The result 150 * may be `supernormal' (as big as 1.111...1 + 1.111...1, or 151 * 11.111...0). If so, a single bit shift-right will fix it 152 * (but remember to adjust the exponent). 153 */ 154 /* r->fp_mant = x->fp_mant + y->fp_mant */ 155 FPU_ADDS(r->fp_mant[3], x->fp_mant[3], y->fp_mant[3]); 156 FPU_ADDCS(r->fp_mant[2], x->fp_mant[2], y->fp_mant[2]); 157 FPU_ADDCS(r->fp_mant[1], x->fp_mant[1], y->fp_mant[1]); 158 FPU_ADDC(r0, x->fp_mant[0], y->fp_mant[0]); 159 if ((r->fp_mant[0] = r0) >= FP_2) { 160 (void) fpu_shr(r, 1); 161 r->fp_exp++; 162 } 163 } else { 164 FPU_DECL_CARRY 165 166 /* 167 * The signs differ, so things are rather more difficult. 168 * H&P would have us negate the negative operand and add; 169 * this is the same as subtracting the negative operand. 170 * This is quite a headache. Instead, we will subtract 171 * y from x, regardless of whether y itself is the negative 172 * operand. When this is done one of three conditions will 173 * hold, depending on the magnitudes of x and y: 174 * case i) |x| > |y|. The result is just x - y, 175 * with x's sign, but it may need to be normalized. 176 * case ii) |x| = |y|. The result is 0 (maybe -0) 177 * so must be fixed up. 178 * case iii) |x| < |y|. We goofed; the result should 179 * be (y - x), with the same sign as y. 180 * We could compare |x| and |y| here and avoid case iii, 181 * but that would take just as much work as the subtract. 182 * We can tell case iii has occurred by an overflow. 183 * 184 * N.B.: since x->fp_exp >= y->fp_exp, x->fp_sticky = 0. 185 */ 186 /* r->fp_mant = x->fp_mant - y->fp_mant */ 187 FPU_SET_CARRY(y->fp_sticky); 188 FPU_SUBCS(r3, x->fp_mant[3], y->fp_mant[3]); 189 FPU_SUBCS(r2, x->fp_mant[2], y->fp_mant[2]); 190 FPU_SUBCS(r1, x->fp_mant[1], y->fp_mant[1]); 191 FPU_SUBC(r0, x->fp_mant[0], y->fp_mant[0]); 192 if (r0 < FP_2) { 193 /* cases i and ii */ 194 if ((r0 | r1 | r2 | r3) == 0) { 195 /* case ii */ 196 r->fp_class = FPC_ZERO; 197 r->fp_sign = rd == FP_RM; 198 return (r); 199 } 200 } else { 201 /* 202 * Oops, case iii. This can only occur when the 203 * exponents were equal, in which case neither 204 * x nor y have sticky bits set. Flip the sign 205 * (to y's sign) and negate the result to get y - x. 206 */ 207 #ifdef DIAGNOSTIC 208 if (x->fp_exp != y->fp_exp || r->fp_sticky) 209 panic("fpu_add"); 210 #endif 211 r->fp_sign = y->fp_sign; 212 FPU_SUBS(r3, 0, r3); 213 FPU_SUBCS(r2, 0, r2); 214 FPU_SUBCS(r1, 0, r1); 215 FPU_SUBC(r0, 0, r0); 216 } 217 r->fp_mant[3] = r3; 218 r->fp_mant[2] = r2; 219 r->fp_mant[1] = r1; 220 r->fp_mant[0] = r0; 221 if (r0 < FP_1) 222 fpu_norm(r); 223 } 224 DUMPFPN(FPE_REG, r); 225 return (r); 226 } 227