Go to most recent revision | Details | Last modification | View Log | RSS feed
| Rev | Author | Line No. | Line |
|---|---|---|---|
| 5222 | serge | 1 | /* flonum_mult.c - multiply two flonums |
| 2 | Copyright 1987, 1990, 1991, 1992, 1995, 2000, 2002, 2003, 2007 |
||
| 3 | Free Software Foundation, Inc. |
||
| 4 | |||
| 5 | This file is part of GAS, the GNU Assembler. |
||
| 6 | |||
| 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. |
||
| 11 | |||
| 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. |
||
| 16 | |||
| 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. */ |
||
| 21 | |||
| 22 | #include "ansidecl.h" |
||
| 23 | #include "flonum.h" |
||
| 24 | |||
| 25 | /* plan for a . b => p(roduct) |
||
| 26 | |||
| 27 | +-------+-------+-/ /-+-------+-------+ |
||
| 28 | | a | a | ... | a | a | |
||
| 29 | | A | A-1 | | 1 | 0 | |
||
| 30 | +-------+-------+-/ /-+-------+-------+ |
||
| 31 | |||
| 32 | +-------+-------+-/ /-+-------+-------+ |
||
| 33 | | b | b | ... | b | b | |
||
| 34 | | B | B-1 | | 1 | 0 | |
||
| 35 | +-------+-------+-/ /-+-------+-------+ |
||
| 36 | |||
| 37 | +-------+-------+-/ /-+-------+-/ /-+-------+-------+ |
||
| 38 | | p | p | ... | p | ... | p | p | |
||
| 39 | | A+B+1| A+B | | N | | 1 | 0 | |
||
| 40 | +-------+-------+-/ /-+-------+-/ /-+-------+-------+ |
||
| 41 | |||
| 42 | /^\ |
||
| 43 | (carry) a .b ... | ... a .b a .b |
||
| 44 | A B | 0 1 0 0 |
||
| 45 | | |
||
| 46 | ... | ... a .b |
||
| 47 | | 1 0 |
||
| 48 | | |
||
| 49 | | ... |
||
| 50 | | |
||
| 51 | | |
||
| 52 | | |
||
| 53 | | ___ |
||
| 54 | | \ |
||
| 55 | +----- P = > a .b |
||
| 56 | N /__ i j |
||
| 57 | |||
| 58 | N = 0 ... A+B |
||
| 59 | |||
| 60 | for all i,j where i+j=N |
||
| 61 | [i,j integers > 0] |
||
| 62 | |||
| 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. |
||
| 67 | |||
| 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 ...) */ |
||
| 72 | |||
| 73 | void |
||
| 74 | flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b, |
||
| 75 | FLONUM_TYPE *product) |
||
| 76 | { |
||
| 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? */ |
||
| 92 | |||
| 93 | if ((a->sign != '-' && a->sign != '+') |
||
| 94 | || (b->sign != '-' && b->sign != '+')) |
||
| 95 | { |
||
| 96 | /* Got to fail somehow. Any suggestions? */ |
||
| 97 | product->sign = 0; |
||
| 98 | return; |
||
| 99 | } |
||
| 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) |
||
| 108 | { |
||
| 109 | P = extra_product_positions; /* P < 0 */ |
||
| 110 | exponent -= extra_product_positions; /* Increases exponent. */ |
||
| 111 | } |
||
| 112 | else |
||
| 113 | { |
||
| 114 | P = 0; |
||
| 115 | } |
||
| 116 | carry = 0; |
||
| 117 | significant = 0; |
||
| 118 | for (N = 0; N <= size_of_sum; N++) |
||
| 119 | { |
||
| 120 | work = carry; |
||
| 121 | carry = 0; |
||
| 122 | for (A = 0; A <= N; A++) |
||
| 123 | { |
||
| 124 | B = N - A; |
||
| 125 | if (A <= size_of_a && B <= size_of_b && B >= 0) |
||
| 126 | { |
||
| 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 |
||
| 141 | } |
||
| 142 | } |
||
| 143 | significant |= work; |
||
| 144 | if (significant || P < 0) |
||
| 145 | { |
||
| 146 | if (P >= 0) |
||
| 147 | { |
||
| 148 | product->low[P] = work; |
||
| 149 | #ifdef TRACE |
||
| 150 | printf ("P=%d. work[p]:=%04x\n", P, work); |
||
| 151 | #endif |
||
| 152 | } |
||
| 153 | P++; |
||
| 154 | } |
||
| 155 | else |
||
| 156 | { |
||
| 157 | extra_product_positions++; |
||
| 158 | exponent++; |
||
| 159 | } |
||
| 160 | } |
||
| 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) |
||
| 167 | { |
||
| 168 | if (extra_product_positions > 0) |
||
| 169 | product->low[P] = carry; |
||
| 170 | else |
||
| 171 | { |
||
| 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--) |
||
| 177 | { |
||
| 178 | work = *q; |
||
| 179 | *q = carry; |
||
| 180 | carry = work; |
||
| 181 | } |
||
| 182 | } |
||
| 183 | } |
||
| 184 | else |
||
| 185 | P--; |
||
| 186 | product->leader = product->low + P; |
||
| 187 | product->exponent = exponent; |
||
| 188 | } |