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Diffstat (limited to 'gnu/usr.bin/as/flonum-mult.c')
| -rw-r--r-- | gnu/usr.bin/as/flonum-mult.c | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/gnu/usr.bin/as/flonum-mult.c b/gnu/usr.bin/as/flonum-mult.c new file mode 100644 index 000000000000..5952bd653dfc --- /dev/null +++ b/gnu/usr.bin/as/flonum-mult.c @@ -0,0 +1,203 @@ +/* flonum_mult.c - multiply two flonums + Copyright (C) 1987, 1990, 1991, 1992 Free Software Foundation, Inc. + + This file is part of Gas, the GNU Assembler. + + The GNU assembler is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY. No author or distributor + accepts responsibility to anyone for the consequences of using it + or for whether it serves any particular purpose or works at all, + unless he says so in writing. Refer to the GNU Assembler General + Public License for full details. + + Everyone is granted permission to copy, modify and redistribute + the GNU Assembler, but only under the conditions described in the + GNU Assembler General Public License. A copy of this license is + supposed to have been given to you along with the GNU Assembler + so you can know your rights and responsibilities. It should be + in a file named COPYING. Among other things, the copyright + notice and this notice must be preserved on all copies. */ + +#ifndef lint +static char rcsid[] = "$Id: flonum-mult.c,v 1.2 1993/11/03 00:51:36 paul Exp $"; +#endif + +#include "flonum.h" + +/* plan for a . b => p(roduct) + + + +-------+-------+-/ /-+-------+-------+ + | a | a | ... | a | a | + | A | A-1 | | 1 | 0 | + +-------+-------+-/ /-+-------+-------+ + + + +-------+-------+-/ /-+-------+-------+ + | b | b | ... | b | b | + | B | B-1 | | 1 | 0 | + +-------+-------+-/ /-+-------+-------+ + + + +-------+-------+-/ /-+-------+-/ /-+-------+-------+ + | p | p | ... | p | ... | p | p | + | A+B+1| A+B | | N | | 1 | 0 | + +-------+-------+-/ /-+-------+-/ /-+-------+-------+ + + /^\ + (carry) a .b ... | ... a .b a .b + A B | 0 1 0 0 + | + ... | ... a .b + | 1 0 + | + | ... + | + | + | + | ___ + | \ + +----- P = > a .b + N /__ i j + + N = 0 ... A+B + + for all i,j where i+j=N + [i,j integers > 0] + + a[], b[], p[] may not intersect. + Zero length factors signify 0 significant bits: treat as 0.0. + 0.0 factors do the right thing. + Zero length product OK. + + I chose the ForTran accent "foo[bar]" instead of the C accent "*garply" + because I felt the ForTran way was more intuitive. The C way would + probably yield better code on most C compilers. Dean Elsner. + (C style also gives deeper insight [to me] ... oh well ...) + */ + +void flonum_multip (a, b, product) +const FLONUM_TYPE *a; +const FLONUM_TYPE *b; +FLONUM_TYPE *product; +{ + int size_of_a; /* 0 origin */ + int size_of_b; /* 0 origin */ + int size_of_product; /* 0 origin */ + int size_of_sum; /* 0 origin */ + int extra_product_positions;/* 1 origin */ + unsigned long work; + unsigned long carry; + long exponent; + LITTLENUM_TYPE * q; + long significant; /* TRUE when we emit a non-0 littlenum */ + /* ForTran accent follows. */ + int P; /* Scan product low-order -> high. */ + int N; /* As in sum above. */ + int A; /* Which [] of a? */ + int B; /* Which [] of b? */ + + if ((a->sign != '-' && a->sign != '+') || (b->sign != '-' && b->sign != '+')) { + /* ... + Got to fail somehow. Any suggestions? */ + product->sign=0; + return; + } + product->sign = (a->sign == b->sign) ? '+' : '-'; + size_of_a = a->leader - a->low; + size_of_b = b->leader - b->low; + exponent = a->exponent + b->exponent; + size_of_product = product->high - product->low; + size_of_sum = size_of_a + size_of_b; + extra_product_positions = size_of_product - size_of_sum; + if (extra_product_positions < 0) + { + P = extra_product_positions; /* P < 0 */ + exponent -= extra_product_positions; /* Increases exponent. */ + } + else + { + P = 0; + } + carry = 0; + significant = 0; + for (N = 0; + N <= size_of_sum; + N++) + { + work = carry; + carry = 0; + for (A = 0; + A <= N; + A ++) + { + B = N - A; + if (A <= size_of_a && B <= size_of_b && B >= 0) + { +#ifdef TRACE + printf("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n", A, a->low[A], B, b->low[B], work); +#endif + work += a->low[A] * b->low[B]; + carry += work >> LITTLENUM_NUMBER_OF_BITS; + work &= LITTLENUM_MASK; +#ifdef TRACE + printf("work=%08x carry=%04x\n", work, carry); +#endif + } + } + significant |= work; + if (significant || P<0) + { + if (P >= 0) + { + product->low[P] = work; +#ifdef TRACE + printf("P=%d. work[p]:=%04x\n", P, work); +#endif + } + P ++; + } + else + { + extra_product_positions ++; + exponent ++; + } + } + /* + * [P]->position # size_of_sum + 1. + * This is where 'carry' should go. + */ +#ifdef TRACE + printf("final carry =%04x\n", carry); +#endif + if (carry) + { + if (extra_product_positions > 0) + { + product->low[P] = carry; + } + else + { + /* No room at high order for carry littlenum. */ + /* Shift right 1 to make room for most significant littlenum. */ + exponent ++; + P --; + for (q = product->low + P; + q >= product->low; + q --) + { + work = * q; + * q = carry; + carry = work; + } + } + } + else + { + P --; + } + product->leader = product->low + P; + product->exponent = exponent; +} + +/* end of flonum_mult.c */ |