| 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 | \f |
| 75 | void |
| 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 */ |