1 /* flonum_mult.c - multiply two flonums
2 Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002
3 Free Software Foundation, Inc.
5 This file is part of Gas, the GNU Assembler.
7 The GNU assembler is distributed in the hope that it will be
8 useful, but WITHOUT ANY WARRANTY. No author or distributor
9 accepts responsibility to anyone for the consequences of using it
10 or for whether it serves any particular purpose or works at all,
11 unless he says so in writing. Refer to the GNU Assembler General
12 Public License for full details.
14 Everyone is granted permission to copy, modify and redistribute
15 the GNU Assembler, but only under the conditions described in the
16 GNU Assembler General Public License. A copy of this license is
17 supposed to have been given to you along with the GNU Assembler
18 so you can know your rights and responsibilities. It should be
19 in a file named COPYING. Among other things, the copyright
20 notice and this notice must be preserved on all copies. */
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 (a
, b
, product
)
79 int size_of_a
; /* 0 origin */
80 int size_of_b
; /* 0 origin */
81 int size_of_product
; /* 0 origin */
82 int size_of_sum
; /* 0 origin */
83 int extra_product_positions
; /* 1 origin */
88 long significant
; /* TRUE when we emit a non-0 littlenum */
89 /* ForTran accent follows. */
90 int P
; /* Scan product low-order -> high. */
91 int N
; /* As in sum above. */
92 int A
; /* Which [] of a? */
93 int B
; /* Which [] of b? */
95 if ((a
->sign
!= '-' && a
->sign
!= '+')
96 || (b
->sign
!= '-' && b
->sign
!= '+'))
98 /* Got to fail somehow. Any suggestions? */
102 product
->sign
= (a
->sign
== b
->sign
) ? '+' : '-';
103 size_of_a
= a
->leader
- a
->low
;
104 size_of_b
= b
->leader
- b
->low
;
105 exponent
= a
->exponent
+ b
->exponent
;
106 size_of_product
= product
->high
- product
->low
;
107 size_of_sum
= size_of_a
+ size_of_b
;
108 extra_product_positions
= size_of_product
- size_of_sum
;
109 if (extra_product_positions
< 0)
111 P
= extra_product_positions
; /* P < 0 */
112 exponent
-= extra_product_positions
; /* Increases exponent. */
120 for (N
= 0; N
<= size_of_sum
; N
++)
124 for (A
= 0; A
<= N
; A
++)
127 if (A
<= size_of_a
&& B
<= size_of_b
&& B
>= 0)
130 printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n",
131 A
, a
->low
[A
], B
, b
->low
[B
], work
);
133 /* Watch out for sign extension! Without the casts, on
134 the DEC Alpha, the multiplication result is *signed*
135 int, which gets sign-extended to convert to the
137 work
+= (unsigned long) a
->low
[A
] * (unsigned long) b
->low
[B
];
138 carry
+= work
>> LITTLENUM_NUMBER_OF_BITS
;
139 work
&= LITTLENUM_MASK
;
141 printf ("work=%08x carry=%04x\n", work
, carry
);
146 if (significant
|| P
< 0)
150 product
->low
[P
] = work
;
152 printf ("P=%d. work[p]:=%04x\n", P
, work
);
159 extra_product_positions
++;
163 /* [P]-> position # size_of_sum + 1.
164 This is where 'carry' should go. */
166 printf ("final carry =%04x\n", carry
);
170 if (extra_product_positions
> 0)
171 product
->low
[P
] = carry
;
174 /* No room at high order for carry littlenum. */
175 /* Shift right 1 to make room for most significant littlenum. */
178 for (q
= product
->low
+ P
; q
>= product
->low
; q
--)
188 product
->leader
= product
->low
+ P
;
189 product
->exponent
= exponent
;
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