39 lines
1.1 KiB
Go
39 lines
1.1 KiB
Go
package world
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// bitArray implements a bitfield array where values are packed into uint64
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// values. If the next value does not fit into remaining space, the remaining
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// space of a uint64 is unused.
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type bitArray struct {
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width uint // bit width of each value
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valsPerElement uint // number of values which fit into a single uint64.
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data []uint64
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}
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// Size returns the number of elements that can fit into the bit array.
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func (b *bitArray) Size() int {
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return int(b.valsPerElement) * len(b.data)
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}
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func (b *bitArray) Set(idx, val uint) {
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var (
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arrayIdx = idx / b.valsPerElement
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startBit = (idx % b.valsPerElement) * b.width
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mask = ^uint64((1<<b.width - 1) << startBit) // set for all bits except target
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)
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b.data[arrayIdx] = (b.data[arrayIdx] & mask) | uint64(val<<startBit)
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}
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func (b *bitArray) Get(idx uint) uint {
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var (
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arrayIdx = idx / b.valsPerElement
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offset = (idx % b.valsPerElement) * b.width
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mask = uint64((1<<b.width - 1) << offset) // set for just the target
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)
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return uint(b.data[arrayIdx]&mask) >> offset
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}
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func valsPerBitArrayElement(bitsPerValue uint) uint {
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return uint(64 / bitsPerValue)
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}
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