mtsatellite/common/coords.go

// Copyright 2014 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.

package common

import (
	"encoding/binary"
	"fmt"
	"strconv"
)

const (
	numBitsPerComponent = 12
	modulo              = 1 << numBitsPerComponent
	maxPositive         = modulo / 2
)

type (
	Coord struct {
		X, Y, Z int16
	}

	KeyTransformer func(int64) int64
	KeyEncoder     func(int64) ([]byte, error)
	KeyDecoder     func([]byte) (int64, error)
	KeySplitter    func(int64) Coord
	KeyJoiner      func(Coord) int64
)

func (c Coord) String() string {
	return fmt.Sprintf("(%d, %d, %d)", c.X, c.Y, c.Z)
}

func (c Coord) Equals(o Coord) bool {
	return c.X == o.X && c.Y == o.Y && c.Z == o.Z
}

// Constructs a database key out of byte slice.
func DecodeStringFromBytes(key []byte) (pos int64, err error) {
	return strconv.ParseInt(string(key), 10, 64)
}

// Encode a block pos to byte slice.
func EncodeStringToBytes(key int64) ([]byte, error) {
	return []byte(strconv.FormatInt(key, 10)), nil
}

func EncodeToBigEndian(key int64) (enc []byte, err error) {
	enc = make([]byte, 8)
	binary.BigEndian.PutUint64(enc, uint64(key))
	return
}

func DecodeFromBigEndian(key []byte) (int64, error) {
	return int64(binary.BigEndian.Uint64(key)), nil
}

func CoordToInterleaved(c Coord) (result int64) {
	const end = 1 << (numBitsPerComponent + 1)
	setmask := int64(1)
	for mask := int16(1); mask != end; mask <<= 1 {
		if c.X&mask != 0 {
			result |= setmask
		}
		setmask <<= 1
		if c.Y&mask != 0 {
			result |= setmask
		}
		setmask <<= 1
		if c.Z&mask != 0 {
			result |= setmask
		}
		setmask <<= 1
	}
	return
}

func InterleavedToCoord(pos int64) Coord {
	const end = 1 << (numBitsPerComponent + 1)
	var x, y, z int16
	for mask := int16(1); mask != end; mask <<= 1 {
		if pos&1 == 1 {
			x |= mask
		}
		pos >>= 1
		if pos&1 == 1 {
			y |= mask
		}
		pos >>= 1
		if pos&1 == 1 {
			z |= mask
		}
		pos >>= 1
	}
	if x >= 1<<numBitsPerComponent {
		x -= end
	}
	if y >= 1<<numBitsPerComponent {
		y -= end
	}
	if z >= 1<<numBitsPerComponent {
		z -= end
	}
	return Coord{X: x, Y: y, Z: z}
}

func CoordToPlain(c Coord) int64 {
	return int64(c.Z)<<(2*numBitsPerComponent) +
		int64(c.Y)<<numBitsPerComponent +
		int64(c.X)
}

func unsignedToSigned(i int16) int16 {
	if i < maxPositive {
		return i
	}
	return i - maxPositive*2
}

// To match C++ code.
func pythonModulo(i int16) int16 {
	const mask = modulo - 1
	if i >= 0 {
		return i & mask
	}
	return modulo - -i&mask
}

func PlainToCoord(i int64) (c Coord) {
	c.X = unsignedToSigned(pythonModulo(int16(i)))
	i = (i - int64(c.X)) >> numBitsPerComponent
	c.Y = unsignedToSigned(pythonModulo(int16(i)))
	i = (i - int64(c.Y)) >> numBitsPerComponent
	c.Z = unsignedToSigned(pythonModulo(int16(i)))
	return
}

func TransformPlainToInterleaved(pos int64) int64 {
	return CoordToInterleaved(PlainToCoord(pos))
}

func TransformInterleavedPlain(pos int64) int64 {
	return CoordToPlain(InterleavedToCoord(pos))
}

func SelectKeySplitter(interleaved bool) KeySplitter {
	if interleaved {
		return InterleavedToCoord
	}
	return PlainToCoord
}

func SelectKeyJoiner(interleaved bool) KeyJoiner {
	if interleaved {
		return CoordToInterleaved
	}
	return CoordToPlain
}

func SelectKeyDecoder(interleaved bool) KeyDecoder {
	if interleaved {
		return DecodeFromBigEndian
	}
	return DecodeStringFromBytes
}

func SelectKeyEncoder(interleaved bool) KeyEncoder {
	if interleaved {
		return EncodeToBigEndian
	}
	return EncodeStringToBytes
}