Binary shift right (* 2) by k bits. k <= maxShift to avoid overflow.
(a *decimal, k uint)
| 107 | |
| 108 | // Binary shift right (* 2) by k bits. k <= maxShift to avoid overflow. |
| 109 | func rightShift(a *decimal, k uint) { |
| 110 | r := 0 // read pointer |
| 111 | w := 0 // write pointer |
| 112 | |
| 113 | // Pick up enough leading digits to cover first shift. |
| 114 | n := 0 |
| 115 | for ; n>>k == 0; r++ { |
| 116 | if r >= a.nd { |
| 117 | if n == 0 { |
| 118 | // a == 0; shouldn't get here, but handle anyway. |
| 119 | a.nd = 0 |
| 120 | return |
| 121 | } |
| 122 | for n>>k == 0 { |
| 123 | n = n * 10 |
| 124 | r++ |
| 125 | } |
| 126 | break |
| 127 | } |
| 128 | c := int(a.d[r]) |
| 129 | n = n*10 + c - '0' |
| 130 | } |
| 131 | a.dp -= r - 1 |
| 132 | |
| 133 | // Pick up a digit, put down a digit. |
| 134 | for ; r < a.nd; r++ { |
| 135 | c := int(a.d[r]) |
| 136 | dig := n >> k |
| 137 | n -= dig << k |
| 138 | a.d[w] = byte(dig + '0') |
| 139 | w++ |
| 140 | n = n*10 + c - '0' |
| 141 | } |
| 142 | |
| 143 | // Put down extra digits. |
| 144 | for n > 0 { |
| 145 | dig := n >> k |
| 146 | n -= dig << k |
| 147 | if w < len(a.d) { |
| 148 | a.d[w] = byte(dig + '0') |
| 149 | w++ |
| 150 | } else if dig > 0 { |
| 151 | a.trunc = true |
| 152 | } |
| 153 | n = n * 10 |
| 154 | } |
| 155 | |
| 156 | a.nd = w |
| 157 | trim(a) |
| 158 | } |
| 159 | |
| 160 | // Cheat sheet for left shift: table indexed by shift count giving |
| 161 | // number of new digits that will be introduced by that shift. |