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util.go
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/
util.go
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package hamt
import (
"math/big"
"math/bits"
)
// hashBits is a helper that allows the reading of the 'next n bits' as an integer.
type hashBits struct {
b []byte
consumed int
}
func mkmask(n int) byte {
return (1 << uint(n)) - 1
}
// Next returns the next 'i' bits of the hashBits value as an integer
func (hb *hashBits) Next(i int) int {
curbi := hb.consumed / 8
leftb := 8 - (hb.consumed % 8)
curb := hb.b[curbi]
if i == leftb {
out := int(mkmask(i) & curb)
hb.consumed += i
return out
} else if i < leftb {
a := curb & mkmask(leftb) // mask out the high bits we don't want
b := a & ^mkmask(leftb-i) // mask out the low bits we don't want
c := b >> uint(leftb-i) // shift whats left down
hb.consumed += i
return int(c)
} else {
out := int(mkmask(leftb) & curb)
out <<= uint(i - leftb)
hb.consumed += leftb
out += hb.Next(i - leftb)
return out
}
}
func popCount(i *big.Int) int {
var n int
for _, v := range i.Bits() {
n += bits.OnesCount64(uint64(v))
}
return n
}