diff options
Diffstat (limited to 'sys/arch/m68k/fpe/fpu_mul.c')
| -rw-r--r-- | sys/arch/m68k/fpe/fpu_mul.c | 226 |
1 files changed, 226 insertions, 0 deletions
diff --git a/sys/arch/m68k/fpe/fpu_mul.c b/sys/arch/m68k/fpe/fpu_mul.c new file mode 100644 index 00000000000..7f150478c3a --- /dev/null +++ b/sys/arch/m68k/fpe/fpu_mul.c @@ -0,0 +1,226 @@ +/* $NetBSD: fpu_mul.c,v 1.1 1995/11/03 04:47:16 briggs Exp $ */ + +/* + * Copyright (c) 1992, 1993 + * The Regents of the University of California. All rights reserved. + * + * This software was developed by the Computer Systems Engineering group + * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and + * contributed to Berkeley. + * + * All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Lawrence Berkeley Laboratory. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in the + * documentation and/or other materials provided with the distribution. + * 3. All advertising materials mentioning features or use of this software + * must display the following acknowledgement: + * This product includes software developed by the University of + * California, Berkeley and its contributors. + * 4. Neither the name of the University nor the names of its contributors + * may be used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND + * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE + * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL + * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS + * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY + * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF + * SUCH DAMAGE. + * + * @(#)fpu_mul.c 8.1 (Berkeley) 6/11/93 + */ + +/* + * Perform an FPU multiply (return x * y). + */ + +#include <sys/types.h> + +#include <machine/reg.h> + +#include "fpu_arith.h" +#include "fpu_emulate.h" + +/* + * The multiplication algorithm for normal numbers is as follows: + * + * The fraction of the product is built in the usual stepwise fashion. + * Each step consists of shifting the accumulator right one bit + * (maintaining any guard bits) and, if the next bit in y is set, + * adding the multiplicand (x) to the accumulator. Then, in any case, + * we advance one bit leftward in y. Algorithmically: + * + * A = 0; + * for (bit = 0; bit < FP_NMANT; bit++) { + * sticky |= A & 1, A >>= 1; + * if (Y & (1 << bit)) + * A += X; + * } + * + * (X and Y here represent the mantissas of x and y respectively.) + * The resultant accumulator (A) is the product's mantissa. It may + * be as large as 11.11111... in binary and hence may need to be + * shifted right, but at most one bit. + * + * Since we do not have efficient multiword arithmetic, we code the + * accumulator as four separate words, just like any other mantissa. + * We use local `register' variables in the hope that this is faster + * than memory. We keep x->fp_mant in locals for the same reason. + * + * In the algorithm above, the bits in y are inspected one at a time. + * We will pick them up 32 at a time and then deal with those 32, one + * at a time. Note, however, that we know several things about y: + * + * - the guard and round bits at the bottom are sure to be zero; + * + * - often many low bits are zero (y is often from a single or double + * precision source); + * + * - bit FP_NMANT-1 is set, and FP_1*2 fits in a word. + * + * We can also test for 32-zero-bits swiftly. In this case, the center + * part of the loop---setting sticky, shifting A, and not adding---will + * run 32 times without adding X to A. We can do a 32-bit shift faster + * by simply moving words. Since zeros are common, we optimize this case. + * Furthermore, since A is initially zero, we can omit the shift as well + * until we reach a nonzero word. + */ +struct fpn * +fpu_mul(fe) + register struct fpemu *fe; +{ + register struct fpn *x = &fe->fe_f1, *y = &fe->fe_f2; + register u_int a3, a2, a1, a0, x3, x2, x1, x0, bit, m; + register int sticky; + FPU_DECL_CARRY + + /* + * Put the `heavier' operand on the right (see fpu_emu.h). + * Then we will have one of the following cases, taken in the + * following order: + * + * - y = NaN. Implied: if only one is a signalling NaN, y is. + * The result is y. + * - y = Inf. Implied: x != NaN (is 0, number, or Inf: the NaN + * case was taken care of earlier). + * If x = 0, the result is NaN. Otherwise the result + * is y, with its sign reversed if x is negative. + * - x = 0. Implied: y is 0 or number. + * The result is 0 (with XORed sign as usual). + * - other. Implied: both x and y are numbers. + * The result is x * y (XOR sign, multiply bits, add exponents). + */ + ORDER(x, y); + if (ISNAN(y)) { + y->fp_sign ^= x->fp_sign; + return (y); + } + if (ISINF(y)) { + if (ISZERO(x)) + return (fpu_newnan(fe)); + y->fp_sign ^= x->fp_sign; + return (y); + } + if (ISZERO(x)) { + x->fp_sign ^= y->fp_sign; + return (x); + } + + /* + * Setup. In the code below, the mask `m' will hold the current + * mantissa byte from y. The variable `bit' denotes the bit + * within m. We also define some macros to deal with everything. + */ + x3 = x->fp_mant[3]; + x2 = x->fp_mant[2]; + x1 = x->fp_mant[1]; + x0 = x->fp_mant[0]; + sticky = a3 = a2 = a1 = a0 = 0; + +#define ADD /* A += X */ \ + FPU_ADDS(a3, a3, x3); \ + FPU_ADDCS(a2, a2, x2); \ + FPU_ADDCS(a1, a1, x1); \ + FPU_ADDC(a0, a0, x0) + +#define SHR1 /* A >>= 1, with sticky */ \ + sticky |= a3 & 1, a3 = (a3 >> 1) | (a2 << 31), \ + a2 = (a2 >> 1) | (a1 << 31), a1 = (a1 >> 1) | (a0 << 31), a0 >>= 1 + +#define SHR32 /* A >>= 32, with sticky */ \ + sticky |= a3, a3 = a2, a2 = a1, a1 = a0, a0 = 0 + +#define STEP /* each 1-bit step of the multiplication */ \ + SHR1; if (bit & m) { ADD; }; bit <<= 1 + + /* + * We are ready to begin. The multiply loop runs once for each + * of the four 32-bit words. Some words, however, are special. + * As noted above, the low order bits of Y are often zero. Even + * if not, the first loop can certainly skip the guard bits. + * The last word of y has its highest 1-bit in position FP_NMANT-1, + * so we stop the loop when we move past that bit. + */ + if ((m = y->fp_mant[3]) == 0) { + /* SHR32; */ /* unneeded since A==0 */ + } else { + bit = 1 << FP_NG; + do { + STEP; + } while (bit != 0); + } + if ((m = y->fp_mant[2]) == 0) { + SHR32; + } else { + bit = 1; + do { + STEP; + } while (bit != 0); + } + if ((m = y->fp_mant[1]) == 0) { + SHR32; + } else { + bit = 1; + do { + STEP; + } while (bit != 0); + } + m = y->fp_mant[0]; /* definitely != 0 */ + bit = 1; + do { + STEP; + } while (bit <= m); + + /* + * Done with mantissa calculation. Get exponent and handle + * 11.111...1 case, then put result in place. We reuse x since + * it already has the right class (FP_NUM). + */ + m = x->fp_exp + y->fp_exp; + if (a0 >= FP_2) { + SHR1; + m++; + } + x->fp_sign ^= y->fp_sign; + x->fp_exp = m; + x->fp_sticky = sticky; + x->fp_mant[3] = a3; + x->fp_mant[2] = a2; + x->fp_mant[1] = a1; + x->fp_mant[0] = a0; + return (x); +} |