URL
https://opencores.org/ocsvn/openrisc/openrisc/trunk
Subversion Repositories openrisc
[/] [openrisc/] [trunk/] [gnu-old/] [binutils-2.18.50/] [gas/] [flonum-mult.c] - Rev 847
Go to most recent revision | Compare with Previous | Blame | View Log
/* flonum_mult.c - multiply two flonums Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007 Free Software Foundation, Inc. This file is part of GAS, the GNU Assembler. GAS is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GAS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GAS; see the file COPYING. If not, write to the Free Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA. */ #include "ansidecl.h" #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, 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 /* Watch out for sign extension! Without the casts, on the DEC Alpha, the multiplication result is *signed* int, which gets sign-extended to convert to the unsigned long! */ work += (unsigned long) a->low[A] * (unsigned long) 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; }
Go to most recent revision | Compare with Previous | Blame | View Log