69 lines
1.4 KiB
Go
69 lines
1.4 KiB
Go
package hamt
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import (
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"fmt"
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"github.com/spaolacci/murmur3"
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"math/bits"
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)
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// hashBits is a helper that allows the reading of the 'next n bits' as an integer.
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type hashBits struct {
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b []byte
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consumed int
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}
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func mkmask(n int) byte {
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return (1 << uint(n)) - 1
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}
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// Next returns the next 'i' bits of the hashBits value as an integer, or an
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// error if there aren't enough bits.
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func (hb *hashBits) Next(i int) (int, error) {
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if hb.consumed+i > len(hb.b)*8 {
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return 0, fmt.Errorf("sharded directory too deep")
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}
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return hb.next(i), nil
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}
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func (hb *hashBits) next(i int) int {
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curbi := hb.consumed / 8
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leftb := 8 - (hb.consumed % 8)
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curb := hb.b[curbi]
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if i == leftb {
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out := int(mkmask(i) & curb)
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hb.consumed += i
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return out
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} else if i < leftb {
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a := curb & mkmask(leftb) // mask out the high bits we don't want
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b := a & ^mkmask(leftb-i) // mask out the low bits we don't want
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c := b >> uint(leftb-i) // shift whats left down
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hb.consumed += i
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return int(c)
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} else {
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out := int(mkmask(leftb) & curb)
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out <<= uint(i - leftb)
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hb.consumed += leftb
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out += hb.next(i - leftb)
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return out
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}
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}
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func logtwo(v int) (int, error) {
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if v <= 0 {
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return 0, fmt.Errorf("hamt size should be a power of two")
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}
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lg2 := bits.TrailingZeros(uint(v))
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if 1<<uint(lg2) != v {
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return 0, fmt.Errorf("hamt size should be a power of two")
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}
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return lg2, nil
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}
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func hash(val []byte) []byte {
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h := murmur3.New64()
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h.Write(val)
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return h.Sum(nil)
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}
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