forked from coracle/nostrlib
fiatjaf
36 lines
918 B
Go
36 lines
918 B
Go
package vector
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import (
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"bytes"
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"cmp"
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"fiatjaf.com/nostr/nip77/negentropy"
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)
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func itemCompare(a, b negentropy.Item) int {
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if a.Timestamp == b.Timestamp {
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return bytes.Compare(a.ID[:], b.ID[:])
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}
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return cmp.Compare(a.Timestamp, b.Timestamp)
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}
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// binary search with custom function
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func searchItemWithBound(items []negentropy.Item, bound negentropy.Bound) int {
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n := len(items)
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// Define x[-1] < target and x[n] >= target.
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// Invariant: x[i-1] < target, x[j] >= target.
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i, j := 0, n
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for i < j {
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h := int(uint(i+j) >> 1) // avoid overflow when computing h
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// i ≤ h < j
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if items[h].Timestamp < bound.Timestamp ||
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(items[h].Timestamp == bound.Timestamp && bytes.Compare(items[h].ID[:], bound.IDPrefix) == -1) {
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i = h + 1 // preserves x[i-1] < target
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} else {
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j = h // preserves x[j] >= target
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}
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}
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// i == j, x[i-1] < target, and x[j] (= x[i]) >= target => answer is i.
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return i
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}
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