96 lines
1.7 KiB
Go
96 lines
1.7 KiB
Go
package polylines
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import (
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"math"
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)
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type chunks []int32
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// Parse splices an integer into chunks
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func (c *chunks) Parse(element int32) {
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c.slice(element, 5)
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}
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// ParseLine converts and splices string into integer chunks
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func (c *chunks) ParseLine(line string) {
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chunkSlice := []int32{}
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for index, letter := range line {
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elementInt := int32(letter) - 63
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if index != len(line)-1 {
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elementInt = elementInt & 31
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}
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chunkSlice = append(chunkSlice, elementInt)
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}
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*c = chunkSlice
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}
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// String returns the chunks as polyline in base64
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func (c *chunks) String() string {
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c.or()
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s := ""
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for i := range *c {
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s += string((*c)[i])
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}
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return s
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}
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// Coordinate converts integer chunks into a single coordinate
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func (c *chunks) Coordinate(precision uint32) float64 {
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resultInt := int32(0)
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for i, element := range *c {
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resultInt += element << uint32(i*5)
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}
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if resultInt&1 == 1 {
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resultInt = ^resultInt
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}
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resultInt = resultInt >> 1
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return float64(resultInt) / math.Pow10(int(precision))
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}
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// slice splits elements into group of "length" bits
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func (c *chunks) slice(element int32, length int) {
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if element == 0 {
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*c = []int32{0}
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return
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}
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chunkSlice := []int32{}
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bitMask := int32(31)
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for i := 0; int32(math.Pow(2, float64(i))) <= element; i += 5 {
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group := (element >> uint(i)) & bitMask
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chunkSlice = append(chunkSlice, group)
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}
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*c = chunkSlice
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}
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// or sets the 6th bit to 1 for every chunk except the last one
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// as indicator bit for coordinate boundaries.
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// It also adds 63 (decimal) to every group to ensure it is in
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// ASCII range
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func (c *chunks) or() {
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for i := range *c {
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if i < len(*c)-1 {
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(*c)[i] = (*c)[i] | 0x20
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}
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(*c)[i] += 63
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}
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}
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