62 lines
1.6 KiB
Go
62 lines
1.6 KiB
Go
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// Copyright (C) 2019 Storj Labs, Inc.
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// See LICENSE for copying information.
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package main
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import (
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"math/bits"
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"github.com/zeebo/errs"
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)
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// errorBitmaskInvalidIdx is the error class to return invalid indexes for the
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// the bitmask type.
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var errorBitmaskInvalidIdx = errs.Class("invalid index")
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// bitmask allows to track indexes in an optimal way.
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type bitmask uint64
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// Set tracks index in mask. It returns an error if index is negative or it's
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// greater than 63.
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func (mask *bitmask) Set(index int) error {
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switch {
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case index < 0:
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return errorBitmaskInvalidIdx.New("negative value (%d)", index)
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case index > 63:
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return errorBitmaskInvalidIdx.New("index is greater than 63 (%d)", index)
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}
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bit := uint64(1) << index
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*mask = bitmask(uint64(*mask) | bit)
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return nil
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}
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// Has returns true if the index is tracked in mask otherwise false.
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// It returns an error if index is negative or it's greater than 63.
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func (mask *bitmask) Has(index int) (bool, error) {
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switch {
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case index < 0:
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return false, errorBitmaskInvalidIdx.New("negative value (%d)", index)
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case index > 63:
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return false, errorBitmaskInvalidIdx.New("index is greater than 63 (%d)", index)
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}
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bit := uint64(1) << index
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bit = uint64(*mask) & bit
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return bit != 0, nil
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}
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// Count returns the number of tracked indexes.
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func (mask *bitmask) Count() int {
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return bits.OnesCount64(uint64(*mask))
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}
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// IsSequence returns true if mask has only tracked a correlative sequence of
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// indexes starting from index 0.
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func (mask *bitmask) IsSequence() bool {
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ones := mask.Count()
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zeros := bits.LeadingZeros64(uint64(*mask))
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return (zeros + ones) == 64
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}
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