nip45: simplify algorithm and hardcode to precision 8.

nip45/helpers.go

@@ -1,23 +1,19 @@
 package nip45
 
-import "math"
+import (
+	"math"
+)
 
 const two32 = 1 << 32
 
-// Extract bits from uint64 using LSB 0 numbering, including lo.
-func eb(bits uint64, hi uint8, lo uint8) uint64 {
-	m := uint64(((1 << (hi - lo)) - 1) << lo)
-	return (bits & m) >> lo
-}
-
 func linearCounting(m uint32, v uint32) float64 {
 	fm := float64(m)
 	return fm * math.Log(fm/float64(v))
 }
 
-func clz64(x uint64) uint8 {
+func clz56(x uint64) uint8 {
 	var c uint8
-	for m := uint64(1 << 63); m&x == 0 && m != 0; m >>= 1 {
+	for m := uint64(1 << 55); m&x == 0 && m != 0; m >>= 1 {
 		c++
 	}
 	return c
@@ -32,25 +28,3 @@ func countZeros(s []uint8) uint32 {
 	}
 	return c
 }
-
-func calculateEstimate(s []uint8) float64 {
-	sum := 0.0
-	for _, val := range s {
-		sum += 1.0 / float64(uint64(1)<<val)
-	}
-
-	m := uint32(len(s))
-	fm := float64(m)
-	return alpha(m) * fm * fm / sum
-}
-
-func alpha(m uint32) float64 {
-	if m == 16 {
-		return 0.673
-	} else if m == 32 {
-		return 0.697
-	} else if m == 64 {
-		return 0.709
-	}
-	return 0.7213 / (1 + 1.079/float64(m))
-}