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