1/* flonum_multip.c - multiply two flonums 2 Copyright (C) 1987 Free Software Foundation, Inc. 3 4This file is part of Gas, the GNU Assembler. 5 6The GNU assembler is distributed in the hope that it will be 7useful, but WITHOUT ANY WARRANTY. No author or distributor 8accepts responsibility to anyone for the consequences of using it 9or for whether it serves any particular purpose or works at all, 10unless he says so in writing. Refer to the GNU Assembler General 11Public License for full details. 12 13Everyone is granted permission to copy, modify and redistribute 14the GNU Assembler, but only under the conditions described in the 15GNU Assembler General Public License. A copy of this license is 16supposed to have been given to you along with the GNU Assembler 17so you can know your rights and responsibilities. It should be 18in a file named COPYING. Among other things, the copyright 19notice 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 64a[], b[], p[] may not intersect. 65Zero length factors signify 0 significant bits: treat as 0.0. 660.0 factors do the right thing. 67Zero length product OK. 68 69I chose the ForTran accent "foo[bar]" instead of the C accent "*garply" 70because I felt the ForTran way was more intuitive. The C way would 71probably yield better code on most C compilers. Dean Elsner. 72(C style also gives deeper insight [to me] ... oh well ...) 73*/ 74 75void 76flonum_multip( 77const_FLONUM_TYPE *a, 78FLONUM_TYPE *b, 79FLONUM_TYPE *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 uint32_t work; 87 uint32_t carry; 88 int32_t exponent; 89 LITTLENUM_TYPE * q; 90 int32_t 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 135printf("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 141printf("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 152printf("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 168printf("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