/* flonum_multip.c - multiply two flonums Copyright (C) 1987 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. */ #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( const_FLONUM_TYPE *a, 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 int work; unsigned long int carry; long int exponent; LITTLENUM_TYPE * q; long int 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: flonum_multip.c */