ml
76 lines
2.2 KiB
Go
76 lines
2.2 KiB
Go
package level
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// BlockPuzzleState describes the state of a block puzzle.
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type BlockPuzzleState struct {
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width int
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height int
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data []byte
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}
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// NewBlockPuzzleState returns a new instance of a block puzzle state modifier.
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// The returned instance works with the passed data slice directly.
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func NewBlockPuzzleState(data []byte, height, width int) *BlockPuzzleState {
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return &BlockPuzzleState{
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data: data,
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width: width,
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height: height}
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}
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// CellValue returns the value of the identified cell.
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func (state *BlockPuzzleState) CellValue(row, col int) int {
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scratch := uint16(0)
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if state.positionOk(row, col) {
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byteOffset, byteShift := state.byteOffset(row, col)
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bitsAvailable := 8 - byteShift
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scratch = uint16(state.data[state.mappedByteIndex(byteOffset)]) >> byteShift
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if bitsAvailable < 3 {
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scratch |= uint16(state.data[state.mappedByteIndex(byteOffset+1)]) << bitsAvailable
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}
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}
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return int(scratch & 7)
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}
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// SetCellValue sets the value of the identified cell.
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func (state *BlockPuzzleState) SetCellValue(row, col int, value int) {
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if state.positionOk(row, col) {
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byteOffset, byteShift := state.byteOffset(row, col)
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needsSecondByte := (8 - byteShift) < 3
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scratch := uint16(state.data[state.mappedByteIndex(byteOffset)])
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mask := uint16(0x0007) << byteShift
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if needsSecondByte {
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scratch |= uint16(state.data[state.mappedByteIndex(byteOffset+1)]) << 8
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}
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scratch = (scratch & ^mask) | (uint16(value) << byteShift)
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state.data[state.mappedByteIndex(byteOffset)] = byte((scratch >> 0) & 0xFF)
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if needsSecondByte {
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state.data[state.mappedByteIndex(byteOffset+1)] = byte((scratch >> 8) & 0xFF)
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}
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}
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}
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func (state *BlockPuzzleState) bitOffset(row, col int) int {
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return (row*state.width + col) * 3
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}
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func (state *BlockPuzzleState) positionOk(row, col int) bool {
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bitOffset := state.bitOffset(row, col)
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return (row < state.height) && (col < state.width) && (bitOffset <= (128 - 3))
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}
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func (state *BlockPuzzleState) byteOffset(row, col int) (byteOffset int, byteShift uint) {
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bitOffset := state.bitOffset(row, col)
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byteOffset = bitOffset / 8
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byteShift = uint(bitOffset % 8)
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return
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}
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func (state *BlockPuzzleState) mappedByteIndex(index int) int {
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remainder := index % 4
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return 15 - (index - remainder + (3 - remainder))
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}
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