| /* flonum_mult.c - multiply two flonums |
| Copyright (C) 1987-2024 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; |
| } |