1 /* flonum_mult.c - multiply two flonums
2 Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007
3 Free Software Foundation, Inc.
5 This file is part of GAS, the GNU Assembler.
7 GAS is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3, or (at your option)
12 GAS is distributed in the hope that it will be useful, but WITHOUT
13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
15 License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GAS; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA
25 /* plan for a . b => p(roduct)
27 +-------+-------+-/ /-+-------+-------+
28 | a | a | ... | a | a |
30 +-------+-------+-/ /-+-------+-------+
32 +-------+-------+-/ /-+-------+-------+
33 | b | b | ... | b | b |
35 +-------+-------+-/ /-+-------+-------+
37 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
38 | p | p | ... | p | ... | p | p |
39 | A+B+1| A+B | | N | | 1 | 0 |
40 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
43 (carry) a .b ... | ... a .b a .b
60 for all i,j where i+j=N
63 a[], b[], p[] may not intersect.
64 Zero length factors signify 0 significant bits: treat as 0.0.
65 0.0 factors do the right thing.
66 Zero length product OK.
68 I chose the ForTran accent "foo[bar]" instead of the C accent "*garply"
69 because I felt the ForTran way was more intuitive. The C way would
70 probably yield better code on most C compilers. Dean Elsner.
71 (C style also gives deeper insight [to me] ... oh well ...) */
74 flonum_multip (const FLONUM_TYPE
*a
, const FLONUM_TYPE
*b
,
77 int size_of_a
; /* 0 origin */
78 int size_of_b
; /* 0 origin */
79 int size_of_product
; /* 0 origin */
80 int size_of_sum
; /* 0 origin */
81 int extra_product_positions
; /* 1 origin */
86 long significant
; /* TRUE when we emit a non-0 littlenum */
87 /* ForTran accent follows. */
88 int P
; /* Scan product low-order -> high. */
89 int N
; /* As in sum above. */
90 int A
; /* Which [] of a? */
91 int B
; /* Which [] of b? */
93 if ((a
->sign
!= '-' && a
->sign
!= '+')
94 || (b
->sign
!= '-' && b
->sign
!= '+'))
96 /* Got to fail somehow. Any suggestions? */
100 product
->sign
= (a
->sign
== b
->sign
) ? '+' : '-';
101 size_of_a
= a
->leader
- a
->low
;
102 size_of_b
= b
->leader
- b
->low
;
103 exponent
= a
->exponent
+ b
->exponent
;
104 size_of_product
= product
->high
- product
->low
;
105 size_of_sum
= size_of_a
+ size_of_b
;
106 extra_product_positions
= size_of_product
- size_of_sum
;
107 if (extra_product_positions
< 0)
109 P
= extra_product_positions
; /* P < 0 */
110 exponent
-= extra_product_positions
; /* Increases exponent. */
118 for (N
= 0; N
<= size_of_sum
; N
++)
122 for (A
= 0; A
<= N
; A
++)
125 if (A
<= size_of_a
&& B
<= size_of_b
&& B
>= 0)
128 printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n",
129 A
, a
->low
[A
], B
, b
->low
[B
], work
);
131 /* Watch out for sign extension! Without the casts, on
132 the DEC Alpha, the multiplication result is *signed*
133 int, which gets sign-extended to convert to the
135 work
+= (unsigned long) a
->low
[A
] * (unsigned long) b
->low
[B
];
136 carry
+= work
>> LITTLENUM_NUMBER_OF_BITS
;
137 work
&= LITTLENUM_MASK
;
139 printf ("work=%08x carry=%04x\n", work
, carry
);
144 if (significant
|| P
< 0)
148 product
->low
[P
] = work
;
150 printf ("P=%d. work[p]:=%04x\n", P
, work
);
157 extra_product_positions
++;
161 /* [P]-> position # size_of_sum + 1.
162 This is where 'carry' should go. */
164 printf ("final carry =%04x\n", carry
);
168 if (extra_product_positions
> 0)
169 product
->low
[P
] = carry
;
172 /* No room at high order for carry littlenum. */
173 /* Shift right 1 to make room for most significant littlenum. */
176 for (q
= product
->low
+ P
; q
>= product
->low
; q
--)
186 product
->leader
= product
->low
+ P
;
187 product
->exponent
= exponent
;
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