93 lines
2.2 KiB
Go
93 lines
2.2 KiB
Go
package save
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import (
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"fmt"
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"math"
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)
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// BitStorage implement the compacted data array used in chunk storage.
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// https://wiki.vg/Chunk_Format
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// This implement the format since Minecraft 1.16
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type BitStorage struct {
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data []uint64
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mask uint64
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bits, size int
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valuesPerLong int
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}
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// NewBitStorage create a new BitStorage.
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// bits is the number of bits per value.
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// size is the number of values.
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// arrl is optional data for initializing.
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// It's length must match the bits and size if it's not nil.
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func NewBitStorage(bits, size int, arrl []uint64) (b *BitStorage) {
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b = &BitStorage{
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mask: 1<<bits - 1,
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bits: bits,
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size: size,
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valuesPerLong: 64 / bits,
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}
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dataLen := (size + b.valuesPerLong - 1) / b.valuesPerLong
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if arrl != nil {
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if len(arrl) != dataLen {
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panic(initBitStorageErr{ArrlLen: len(arrl), WantLen: dataLen})
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}
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b.data = arrl
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} else {
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b.data = make([]uint64, dataLen)
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}
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return
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}
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type initBitStorageErr struct {
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ArrlLen int
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WantLen int
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}
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func (i initBitStorageErr) Error() string {
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return fmt.Sprintf("invalid length given for storage, got: %d but expected: %d", i.ArrlLen, i.WantLen)
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}
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func (b *BitStorage) cellIndex(n int) int {
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elemPerLong := 64 / b.bits
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return n / elemPerLong
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}
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// Swap sets v into [i], and return the previous [i] value.
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func (b *BitStorage) Swap(i, v int) (old int) {
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if i < 0 || i > b.size-1 ||
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v < 0 || uint64(v) > b.mask {
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panic("out of bounds")
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}
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c := b.cellIndex(i)
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l := b.data[c]
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offset := uint64((i - c*b.valuesPerLong) * b.bits)
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old = int(l >> offset & b.mask)
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b.data[c] = l&(b.mask<<offset^math.MaxUint64) | (uint64(v)&b.mask)<<offset
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return
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}
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// Set sets v into [i]
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func (b *BitStorage) Set(i, v int) {
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if i < 0 || i > b.size-1 ||
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v < 0 || uint64(v) > b.mask {
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panic("out of bounds")
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}
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c := b.cellIndex(i)
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l := b.data[c]
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offset := (i - c*b.valuesPerLong) * b.bits
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b.data[c] = l&(b.mask<<offset^math.MaxUint64) | (uint64(v)&b.mask)<<offset
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}
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// Get gets [i] value.
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func (b *BitStorage) Get(i int) int {
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if i < 0 || i > b.size-1 {
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panic("out of bounds")
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}
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c := b.cellIndex(i)
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l := b.data[c]
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offset := (i - c*b.valuesPerLong) * b.bits
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return int(l >> offset & b.mask)
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}
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