0,0 → 1,188 |
/* flonum_mult.c - multiply two flonums |
Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007 |
Free Software Foundation, Inc. |
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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. */ |
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#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; |
} |