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| 5222 | serge | 1 | /* flonum_mult.c - multiply two flonums |
| 6324 | serge | 2 | Copyright (C) 1987-2015 Free Software Foundation, Inc. |
| 5222 | serge | 3 | |
| 4 | This file is part of GAS, the GNU Assembler. |
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| 5 | |||
| 6 | GAS is free software; you can redistribute it and/or modify |
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| 7 | it under the terms of the GNU General Public License as published by |
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| 8 | the Free Software Foundation; either version 3, or (at your option) |
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| 9 | any later version. |
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| 10 | |||
| 11 | GAS is distributed in the hope that it will be useful, but WITHOUT |
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| 12 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
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| 13 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public |
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| 14 | License for more details. |
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| 15 | |||
| 16 | You should have received a copy of the GNU General Public License |
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| 17 | along with GAS; see the file COPYING. If not, write to the Free |
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| 18 | Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA |
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| 19 | 02110-1301, USA. */ |
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| 20 | |||
| 21 | #include "ansidecl.h" |
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| 22 | #include "flonum.h" |
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| 23 | |||
| 24 | /* plan for a . b => p(roduct) |
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| 25 | |||
| 26 | +-------+-------+-/ /-+-------+-------+ |
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| 27 | | a | a | ... | a | a | |
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| 28 | | A | A-1 | | 1 | 0 | |
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| 29 | +-------+-------+-/ /-+-------+-------+ |
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| 30 | |||
| 31 | +-------+-------+-/ /-+-------+-------+ |
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| 32 | | b | b | ... | b | b | |
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| 33 | | B | B-1 | | 1 | 0 | |
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| 34 | +-------+-------+-/ /-+-------+-------+ |
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| 35 | |||
| 36 | +-------+-------+-/ /-+-------+-/ /-+-------+-------+ |
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| 37 | | p | p | ... | p | ... | p | p | |
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| 38 | | A+B+1| A+B | | N | | 1 | 0 | |
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| 39 | +-------+-------+-/ /-+-------+-/ /-+-------+-------+ |
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| 40 | |||
| 41 | /^\ |
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| 42 | (carry) a .b ... | ... a .b a .b |
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| 43 | A B | 0 1 0 0 |
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| 44 | | |
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| 45 | ... | ... a .b |
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| 46 | | 1 0 |
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| 47 | | |
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| 48 | | ... |
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| 49 | | |
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| 50 | | |
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| 51 | | |
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| 52 | | ___ |
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| 53 | | \ |
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| 54 | +----- P = > a .b |
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| 55 | N /__ i j |
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| 56 | |||
| 57 | N = 0 ... A+B |
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| 58 | |||
| 59 | for all i,j where i+j=N |
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| 60 | [i,j integers > 0] |
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| 61 | |||
| 62 | a[], b[], p[] may not intersect. |
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| 63 | Zero length factors signify 0 significant bits: treat as 0.0. |
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| 64 | 0.0 factors do the right thing. |
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| 65 | Zero length product OK. |
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| 66 | |||
| 67 | I chose the ForTran accent "foo[bar]" instead of the C accent "*garply" |
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| 68 | because I felt the ForTran way was more intuitive. The C way would |
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| 69 | probably yield better code on most C compilers. Dean Elsner. |
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| 70 | (C style also gives deeper insight [to me] ... oh well ...) */ |
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| 71 | |||
| 72 | void |
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| 73 | flonum_multip (const FLONUM_TYPE *a, const FLONUM_TYPE *b, |
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| 74 | FLONUM_TYPE *product) |
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| 75 | { |
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| 76 | int size_of_a; /* 0 origin */ |
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| 77 | int size_of_b; /* 0 origin */ |
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| 78 | int size_of_product; /* 0 origin */ |
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| 79 | int size_of_sum; /* 0 origin */ |
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| 80 | int extra_product_positions; /* 1 origin */ |
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| 81 | unsigned long work; |
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| 82 | unsigned long carry; |
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| 83 | long exponent; |
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| 84 | LITTLENUM_TYPE *q; |
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| 85 | long significant; /* TRUE when we emit a non-0 littlenum */ |
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| 86 | /* ForTran accent follows. */ |
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| 87 | int P; /* Scan product low-order -> high. */ |
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| 88 | int N; /* As in sum above. */ |
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| 89 | int A; /* Which [] of a? */ |
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| 90 | int B; /* Which [] of b? */ |
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| 91 | |||
| 92 | if ((a->sign != '-' && a->sign != '+') |
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| 93 | || (b->sign != '-' && b->sign != '+')) |
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| 94 | { |
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| 95 | /* Got to fail somehow. Any suggestions? */ |
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| 96 | product->sign = 0; |
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| 97 | return; |
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| 98 | } |
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| 99 | product->sign = (a->sign == b->sign) ? '+' : '-'; |
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| 100 | size_of_a = a->leader - a->low; |
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| 101 | size_of_b = b->leader - b->low; |
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| 102 | exponent = a->exponent + b->exponent; |
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| 103 | size_of_product = product->high - product->low; |
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| 104 | size_of_sum = size_of_a + size_of_b; |
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| 105 | extra_product_positions = size_of_product - size_of_sum; |
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| 106 | if (extra_product_positions < 0) |
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| 107 | { |
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| 108 | P = extra_product_positions; /* P < 0 */ |
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| 109 | exponent -= extra_product_positions; /* Increases exponent. */ |
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| 110 | } |
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| 111 | else |
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| 112 | { |
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| 113 | P = 0; |
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| 114 | } |
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| 115 | carry = 0; |
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| 116 | significant = 0; |
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| 117 | for (N = 0; N <= size_of_sum; N++) |
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| 118 | { |
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| 119 | work = carry; |
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| 120 | carry = 0; |
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| 121 | for (A = 0; A <= N; A++) |
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| 122 | { |
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| 123 | B = N - A; |
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| 124 | if (A <= size_of_a && B <= size_of_b && B >= 0) |
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| 125 | { |
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| 126 | #ifdef TRACE |
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| 127 | printf ("a:low[%d.]=%04x b:low[%d.]=%04x work_before=%08x\n", |
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| 128 | A, a->low[A], B, b->low[B], work); |
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| 129 | #endif |
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| 130 | /* Watch out for sign extension! Without the casts, on |
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| 131 | the DEC Alpha, the multiplication result is *signed* |
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| 132 | int, which gets sign-extended to convert to the |
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| 133 | unsigned long! */ |
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| 134 | work += (unsigned long) a->low[A] * (unsigned long) b->low[B]; |
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| 135 | carry += work >> LITTLENUM_NUMBER_OF_BITS; |
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| 136 | work &= LITTLENUM_MASK; |
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| 137 | #ifdef TRACE |
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| 138 | printf ("work=%08x carry=%04x\n", work, carry); |
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| 139 | #endif |
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| 140 | } |
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| 141 | } |
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| 142 | significant |= work; |
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| 143 | if (significant || P < 0) |
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| 144 | { |
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| 145 | if (P >= 0) |
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| 146 | { |
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| 147 | product->low[P] = work; |
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| 148 | #ifdef TRACE |
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| 149 | printf ("P=%d. work[p]:=%04x\n", P, work); |
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| 150 | #endif |
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| 151 | } |
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| 152 | P++; |
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| 153 | } |
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| 154 | else |
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| 155 | { |
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| 156 | extra_product_positions++; |
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| 157 | exponent++; |
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| 158 | } |
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| 159 | } |
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| 160 | /* [P]-> position # size_of_sum + 1. |
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| 161 | This is where 'carry' should go. */ |
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| 162 | #ifdef TRACE |
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| 163 | printf ("final carry =%04x\n", carry); |
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| 164 | #endif |
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| 165 | if (carry) |
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| 166 | { |
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| 167 | if (extra_product_positions > 0) |
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| 168 | product->low[P] = carry; |
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| 169 | else |
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| 170 | { |
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| 171 | /* No room at high order for carry littlenum. */ |
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| 172 | /* Shift right 1 to make room for most significant littlenum. */ |
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| 173 | exponent++; |
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| 174 | P--; |
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| 175 | for (q = product->low + P; q >= product->low; q--) |
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| 176 | { |
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| 177 | work = *q; |
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| 178 | *q = carry; |
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| 179 | carry = work; |
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| 180 | } |
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| 181 | } |
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| 182 | } |
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| 183 | else |
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| 184 | P--; |
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| 185 | product->leader = product->low + P; |
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| 186 | product->exponent = exponent; |
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| 187 | } |