70 lines
1.4 KiB
Text
70 lines
1.4 KiB
Text
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package gc
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type color uint8
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const (
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white = iota
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gray
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black
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)
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func tricolor(roots []string, all []string, refs map[string][]string) []string {
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// all objects white -> default value of color
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state := make(map[string]color, len(all))
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var (
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grays []string
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reachable []string
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)
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grays = append(grays, roots...)
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// root-set objects gray.
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for _, ro := range roots {
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state[ro] = gray
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}
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// (Repeat this as long as there are gray coloured objects) Pick a gray
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// object. Colour all objects referenced to from that gray object gray too.
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// (Except those who are black). And colour itself black.
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// Pick any gray object
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for id := findcolor(state, gray); id != ""; id = findcolor(state, gray) {
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// mark all the referenced objects as gray
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for _, target := range refs[id] {
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if state[target] == white {
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state[target] = gray
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}
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}
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state[id] = black
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}
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// All black objects are now reachable, and all white objects are
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// unreachable. Free those that are white!
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var whites []string
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for _, obj := range all {
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if state[obj] == white {
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whites = append(whites, obj)
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}
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}
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return whites
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}
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func findcolor(cs map[string]color, q color) string {
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// TODO(stevvooe): Super-inefficient!
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for id, c := range cs {
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if c == q {
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return id
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}
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}
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return ""
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}
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// type colorset struct {
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// state map[string]color
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// }
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// func (cs *colorset) mark(id string, c color) {
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// cs.state[id] = c
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// }
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