Merge pull request #11 from gammazero/bitmath
Bitwise math for speed
Evan Huus authored 7 years ago
GitHub committed 7 years ago
| 6 | 6 | */ |
| 7 | 7 | package queue |
| 8 | 8 | |
| 9 | // minQueueLen is smallest capacity that queue may have. | |
| 10 | // Must be power of 2 for bitwise modulus: x % n == x & (n - 1). | |
| 9 | 11 | const minQueueLen = 16 |
| 10 | 12 | |
| 11 | 13 | // Queue represents a single instance of the queue data structure. |
| 29 | 31 | // resizes the queue to fit exactly twice its current contents |
| 30 | 32 | // this can result in shrinking if the queue is less than half-full |
| 31 | 33 | func (q *Queue) resize() { |
| 32 | newBuf := make([]interface{}, q.count*2) | |
| 34 | newBuf := make([]interface{}, q.count<<1) | |
| 33 | 35 | |
| 34 | 36 | if q.tail > q.head { |
| 35 | 37 | copy(newBuf, q.buf[q.head:q.tail]) |
| 50 | 52 | } |
| 51 | 53 | |
| 52 | 54 | q.buf[q.tail] = elem |
| 53 | q.tail = (q.tail + 1) % len(q.buf) | |
| 55 | // bitwise modulus | |
| 56 | q.tail = (q.tail + 1) & (len(q.buf) - 1) | |
| 54 | 57 | q.count++ |
| 55 | 58 | } |
| 56 | 59 | |
| 75 | 78 | if i < 0 || i >= q.count { |
| 76 | 79 | panic("queue: Get() called with index out of range") |
| 77 | 80 | } |
| 78 | return q.buf[(q.head+i)%len(q.buf)] | |
| 81 | // bitwise modulus | |
| 82 | return q.buf[(q.head+i)&(len(q.buf)-1)] | |
| 79 | 83 | } |
| 80 | 84 | |
| 81 | 85 | // Remove removes the element from the front of the queue. If you actually |
| 85 | 89 | panic("queue: Remove() called on empty queue") |
| 86 | 90 | } |
| 87 | 91 | q.buf[q.head] = nil |
| 88 | q.head = (q.head + 1) % len(q.buf) | |
| 92 | // bitwise modulus | |
| 93 | q.head = (q.head + 1) & (len(q.buf) - 1) | |
| 89 | 94 | q.count-- |
| 90 | if len(q.buf) > minQueueLen && q.count*4 == len(q.buf) { | |
| 95 | // Resize down if buffer 1/4 full. | |
| 96 | if len(q.buf) > minQueueLen && (q.count<<2) == len(q.buf) { | |
| 91 | 97 | q.resize() |
| 92 | 98 | } |
| 93 | 99 | } |