daily update
[binutils.git] / gas / flonum-mult.c
blobe5f32fca2e4a25cc6728e3ea064b1afcdaf5f41f
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)
10 any later version.
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
20 02110-1301, USA. */
22 #include "ansidecl.h"
23 #include "flonum.h"
25 /* plan for a . b => p(roduct)
27 +-------+-------+-/ /-+-------+-------+
28 | a | a | ... | a | a |
29 | A | A-1 | | 1 | 0 |
30 +-------+-------+-/ /-+-------+-------+
32 +-------+-------+-/ /-+-------+-------+
33 | b | b | ... | b | b |
34 | B | B-1 | | 1 | 0 |
35 +-------+-------+-/ /-+-------+-------+
37 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
38 | p | p | ... | p | ... | p | p |
39 | A+B+1| A+B | | N | | 1 | 0 |
40 +-------+-------+-/ /-+-------+-/ /-+-------+-------+
42 /^\
43 (carry) a .b ... | ... a .b a .b
44 A B | 0 1 0 0
46 ... | ... a .b
47 | 1 0
49 | ...
53 | ___
54 | \
55 +----- P = > a .b
56 N /__ i j
58 N = 0 ... A+B
60 for all i,j where i+j=N
61 [i,j integers > 0]
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 ...) */
73 void
74 flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b,
75 FLONUM_TYPE *product)
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 */
82 unsigned long work;
83 unsigned long carry;
84 long exponent;
85 LITTLENUM_TYPE *q;
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? */
97 product->sign = 0;
98 return;
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. */
112 else
114 P = 0;
116 carry = 0;
117 significant = 0;
118 for (N = 0; N <= size_of_sum; N++)
120 work = carry;
121 carry = 0;
122 for (A = 0; A <= N; A++)
124 B = N - A;
125 if (A <= size_of_a && B <= size_of_b && B >= 0)
127 #ifdef TRACE
128 printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n",
129 A, a->low[A], B, b->low[B], work);
130 #endif
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
134 unsigned long! */
135 work += (unsigned long) a->low[A] * (unsigned long) b->low[B];
136 carry += work >> LITTLENUM_NUMBER_OF_BITS;
137 work &= LITTLENUM_MASK;
138 #ifdef TRACE
139 printf ("work=%08x carry=%04x\n", work, carry);
140 #endif
143 significant |= work;
144 if (significant || P < 0)
146 if (P >= 0)
148 product->low[P] = work;
149 #ifdef TRACE
150 printf ("P=%d. work[p]:=%04x\n", P, work);
151 #endif
153 P++;
155 else
157 extra_product_positions++;
158 exponent++;
161 /* [P]-> position # size_of_sum + 1.
162 This is where 'carry' should go. */
163 #ifdef TRACE
164 printf ("final carry =%04x\n", carry);
165 #endif
166 if (carry)
168 if (extra_product_positions > 0)
169 product->low[P] = carry;
170 else
172 /* No room at high order for carry littlenum. */
173 /* Shift right 1 to make room for most significant littlenum. */
174 exponent++;
175 P--;
176 for (q = product->low + P; q >= product->low; q--)
178 work = *q;
179 *q = carry;
180 carry = work;
184 else
185 P--;
186 product->leader = product->low + P;
187 product->exponent = exponent;