64 lines
1.5 KiB
Go
64 lines
1.5 KiB
Go
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package lookup
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import "context"
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// FluzCapacitorAlgorithm works by narrowing the epoch search area if an update is found
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// going back and forth in time
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// First, it will attempt to find an update where it should be now if the hint was
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// really the last update. If that lookup fails, then the last update must be either the hint itself
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// or the epochs right below. If however, that lookup succeeds, then the update must be
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// that one or within the epochs right below.
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// see the guide for a more graphical representation
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func FluzCapacitorAlgorithm(ctx context.Context, now uint64, hint Epoch, read ReadFunc) (value interface{}, err error) {
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var lastFound interface{}
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var epoch Epoch
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if hint == NoClue {
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hint = worstHint
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}
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t := now
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for {
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epoch = GetNextEpoch(hint, t)
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value, err = read(ctx, epoch, now)
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if err != nil {
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return nil, err
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}
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if value != nil {
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lastFound = value
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if epoch.Level == LowestLevel || epoch.Equals(hint) {
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return value, nil
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}
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hint = epoch
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continue
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}
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if epoch.Base() == hint.Base() {
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if lastFound != nil {
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return lastFound, nil
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}
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// we have reached the hint itself
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if hint == worstHint {
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return nil, nil
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}
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// check it out
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value, err = read(ctx, hint, now)
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if err != nil {
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return nil, err
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}
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if value != nil {
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return value, nil
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}
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// bad hint.
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t = hint.Base()
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hint = worstHint
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continue
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}
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base := epoch.Base()
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if base == 0 {
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return nil, nil
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}
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t = base - 1
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}
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}
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