55 lines
1.2 KiB
Go
55 lines
1.2 KiB
Go
package iterator
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// IndexProvider implements a subset of the Interator interface
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type IndexProvider interface {
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StartIndex() int
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EndIndex() int
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}
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// FixBounds will force the index i to either its lower- or upper-bound value
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// if out-of-bound
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func FixBounds(i, lower, upper int) int {
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switch {
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case i > upper:
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i = upper
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case i < lower:
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i = lower
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}
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return i
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}
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// WrapBounds will wrap the index i around its upper- or lower-bound if
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// out-of-bound
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func WrapBounds(i, lower, upper int) int {
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if upper <= 0 {
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return lower
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}
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switch {
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case i > upper:
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i = lower + (i-upper-1)%upper
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case i < lower:
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i = upper - (lower-i-1)%upper
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}
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return i
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}
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type BoundsCheckFunc func(int, int, int) int
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// MoveIndex moves the index variable idx forward by delta steps and ensures
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// that the boundary policy as defined by the CheckBoundsFunc is enforced.
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//
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// If CheckBoundsFunc is nil, fix boundary checks are performed.
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func MoveIndex(idx, delta int, indexer IndexProvider, cb BoundsCheckFunc) int {
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lower, upper := indexer.StartIndex(), indexer.EndIndex()
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sign := 1
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if upper < lower {
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lower, upper = upper, lower
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sign = -1
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}
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result := idx + sign*delta
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if cb == nil {
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return FixBounds(result, lower, upper)
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}
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return cb(result, lower, upper)
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}
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