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Reduce runtime of go Encode() implementation by 20% #566

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merged 2 commits into from
Dec 6, 2024
Merged

Reduce runtime of go Encode() implementation by 20% #566

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e4a8bba
Reduce runtime of Encode() by 20%
willbeason Nov 8, 2023
6d7bafc
Merge branch 'main' into optimize-rebased
drinckes Dec 6, 2024
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29 changes: 20 additions & 9 deletions go/encode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,9 @@ func Encode(lat, lng float64, codeLen int) string {
}
// Use a char array so we can build it up from the end digits, without having
// to keep reallocating strings.
var code [15]byte
var code [16]byte
// Avoid the need for string concatenation by filling in the Separator manually.
code[sepPos] = Separator

// Compute the code.
// This approach converts each value to an integer after multiplying it by
Expand All @@ -74,8 +76,8 @@ func Encode(lat, lng float64, codeLen int) string {
var latVal int64 = int64(math.Round((lat+latMax)*finalLatPrecision*1e6) / 1e6)
var lngVal int64 = int64(math.Round((lng+lngMax)*finalLngPrecision*1e6) / 1e6)

pos := maxCodeLen - 1
// Compute the grid part of the code if necessary.
pos := maxCodeLen
if codeLen > pairCodeLen {
for i := 0; i < gridCodeLen; i++ {
latDigit := latVal % int64(gridRows)
Expand All @@ -90,22 +92,31 @@ func Encode(lat, lng float64, codeLen int) string {
latVal /= gridLatFullValue
lngVal /= gridLngFullValue
}
pos = pairCodeLen - 1

// Compute the pair after the Separator as a special case rather than
// introduce an if statement to the loop which will only be executed once.
// This also allows us to remove two unnecessary divides at the end of the loop.
latNdx := latVal % int64(encBase)
lngNdx := lngVal % int64(encBase)
code[sepPos+2] = Alphabet[lngNdx]
code[sepPos+1] = Alphabet[latNdx]

// Compute the pair section of the code.
for i := 0; i < pairCodeLen/2; i++ {
latNdx := latVal % int64(encBase)
lngNdx := lngVal % int64(encBase)
pos = sepPos - 1
for i := 0; i < sepPos/2; i++ {
latVal /= int64(encBase)
lngVal /= int64(encBase)
latNdx = latVal % int64(encBase)
lngNdx = lngVal % int64(encBase)
code[pos] = Alphabet[lngNdx]
pos -= 1
code[pos] = Alphabet[latNdx]
pos -= 1
latVal /= int64(encBase)
lngVal /= int64(encBase)
}

// If we don't need to pad the code, return the requested section.
if codeLen >= sepPos {
return string(code[:sepPos]) + string(Separator) + string(code[sepPos:codeLen])
return string(code[:codeLen+1])
}
// Pad and return the code.
return string(code[:codeLen]) + strings.Repeat(string(Padding), sepPos-codeLen) + string(Separator)
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