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package passwordvalidator
import (
"math"
)
// GetEntropy returns the entropy in bits for the given password
// See the ReadMe for more information
func GetEntropy(password string) float64 {
return getEntropy(password)
}
func getEntropy(password string) float64 {
base := getBase(password)
length := getLength(password)
// calculate log2(base^length)
return logPow(float64(base), length, 2)
}
func logX(base, n float64) float64 {
if base == 0 {
return 0
}
// change of base formulae
return math.Log2(n) / math.Log2(base)
}
// logPow calculates log_base(x^y)
// without leaving logspace for each multiplication step
// this makes it take less space in memory
func logPow(expBase float64, pow int, logBase float64) float64 {
// logb (MN) = logb M + logb N
total := 0.0
for i := 0; i < pow; i++ {
total += logX(logBase, expBase)
}
return total
}
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