1 /* flonum_multip.c - multiply two flonums
2 Copyright (C) 1987 Free Software Foundation, Inc.
3
4 This file is part of Gas, the GNU Assembler.
5
6 The GNU assembler is distributed in the hope that it will be
7 useful, but WITHOUT ANY WARRANTY. No author or distributor
8 accepts responsibility to anyone for the consequences of using it
9 or for whether it serves any particular purpose or works at all,
10 unless he says so in writing. Refer to the GNU Assembler General
11 Public License for full details.
12
13 Everyone is granted permission to copy, modify and redistribute
14 the GNU Assembler, but only under the conditions described in the
15 GNU Assembler General Public License. A copy of this license is
16 supposed to have been given to you along with the GNU Assembler
17 so you can know your rights and responsibilities. It should be
18 in a file named COPYING. Among other things, the copyright
19 notice and this notice must be preserved on all copies. */
20
21 #include "flonum.h"
22
23 /* plan for a . b => p(roduct)
24
25
26 +-------+-------+-/ /-+-------+-------+
27 | a | a | ... | a | a |
28 | A | A-1 | | 1 | 0 |
29 +-------+-------+-/ /-+-------+-------+
30
31
32 +-------+-------+-/ /-+-------+-------+
33 | b | b | ... | b | b |
34 | B | B-1 | | 1 | 0 |
35 +-------+-------+-/ /-+-------+-------+
36
37
38 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
39 | p | p | ... | p | ... | p | p |
40 | A+B+1| A+B | | N | | 1 | 0 |
41 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
42
43 /^\
44 (carry) a .b ... | ... a .b a .b
45 A B | 0 1 0 0
46 |
47 ... | ... a .b
48 | 1 0
49 |
50 | ...
51 |
52 |
53 |
54 | ___
55 | \
56 +----- P = > a .b
57 N /__ i j
58
59 N = 0 ... A+B
60
61 for all i,j where i+j=N
62 [i,j integers > 0]
63
64 a[], b[], p[] may not intersect.
65 Zero length factors signify 0 significant bits: treat as 0.0.
66 0.0 factors do the right thing.
67 Zero length product OK.
68
69 I chose the ForTran accent "foo[bar]" instead of the C accent "*garply"
70 because I felt the ForTran way was more intuitive. The C way would
71 probably yield better code on most C compilers. Dean Elsner.
72 (C style also gives deeper insight [to me] ... oh well ...)
73 */
74
75 void
flonum_multip(a,b,product)76 flonum_multip (a, b, product)
77 FLONUM_TYPE * a,
78 * b,
79 * product;
80 {
81 int size_of_a; /* 0 origin */
82 int size_of_b; /* 0 origin */
83 int size_of_product; /* 0 origin */
84 int size_of_sum; /* 0 origin */
85 int extra_product_positions;/* 1 origin */
86 unsigned long int work;
87 unsigned long int carry;
88 long int exponent;
89 LITTLENUM_TYPE * q;
90 long int significant; /* TRUE when we emit a non-0 littlenum */
91 /* ForTran accent follows. */
92 int P; /* Scan product low-order -> high. */
93 int N; /* As in sum above. */
94 int A; /* Which [] of a? */
95 int B; /* Which [] of b? */
96
97 if((a->sign!='-' && a->sign!='+') || (b->sign!='-' && b->sign!='+')) {
98 /* ...
99 Got to fail somehow. Any suggestions? */
100 product->sign=0;
101 return;
102 }
103 product -> sign = (a->sign == b->sign) ? '+' : '-';
104 size_of_a = a -> leader - a -> low;
105 size_of_b = b -> leader - b -> low;
106 exponent = a -> exponent + b -> exponent;
107 size_of_product = product -> high - product -> low;
108 size_of_sum = size_of_a + size_of_b;
109 extra_product_positions = size_of_product - size_of_sum;
110 if (extra_product_positions < 0)
111 {
112 P = extra_product_positions; /* P < 0 */
113 exponent -= extra_product_positions; /* Increases exponent. */
114 }
115 else
116 {
117 P = 0;
118 }
119 carry = 0;
120 significant = 0;
121 for (N = 0;
122 N <= size_of_sum;
123 N++)
124 {
125 work = carry;
126 carry = 0;
127 for (A = 0;
128 A <= N;
129 A ++)
130 {
131 B = N - A;
132 if (A <= size_of_a && B <= size_of_b && B >= 0)
133 {
134 #ifdef TRACE
135 printf("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n", A, a->low[A], B, b->low[B], work);
136 #endif
137 work += a -> low [A] * b -> low [B];
138 carry += work >> LITTLENUM_NUMBER_OF_BITS;
139 work &= LITTLENUM_MASK;
140 #ifdef TRACE
141 printf("work=%08x carry=%04x\n", work, carry);
142 #endif
143 }
144 }
145 significant |= work;
146 if (significant || P<0)
147 {
148 if (P >= 0)
149 {
150 product -> low [P] = work;
151 #ifdef TRACE
152 printf("P=%d. work[p]:=%04x\n", P, work);
153 #endif
154 }
155 P ++;
156 }
157 else
158 {
159 extra_product_positions ++;
160 exponent ++;
161 }
162 }
163 /*
164 * [P]-> position # size_of_sum + 1.
165 * This is where 'carry' should go.
166 */
167 #ifdef TRACE
168 printf("final carry =%04x\n", carry);
169 #endif
170 if (carry)
171 {
172 if (extra_product_positions > 0)
173 {
174 product -> low [P] = carry;
175 }
176 else
177 {
178 /* No room at high order for carry littlenum. */
179 /* Shift right 1 to make room for most significant littlenum. */
180 exponent ++;
181 P --;
182 for (q = product -> low + P;
183 q >= product -> low;
184 q --)
185 {
186 work = * q;
187 * q = carry;
188 carry = work;
189 }
190 }
191 }
192 else
193 {
194 P --;
195 }
196 product -> leader = product -> low + P;
197 product -> exponent = exponent;
198 }
199
200 /* end: flonum_multip.c */
201