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index/suffixarray: use sort.Search

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R=gri
CC=golang-dev
https://golang.org/cl/3200041
This commit is contained in:
Russ Cox 2010-11-19 16:04:25 -05:00
parent 07791d04d6
commit b51f0c5cca
1 changed files with 2 additions and 20 deletions
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22
src/pkg/index/suffixarray/suffixarray.go
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@ -54,21 +54,8 @@ func (x *Index) at(i int) []byte {
} }
// Binary search according to "A Method of Programming", E.W. Dijkstra.
func (x *Index) search(s []byte) int { func (x *Index) search(s []byte) int {
i, j := 0, len(x.sa) return sort.Search(len(x.sa), func(i int) bool { return bytes.Compare(x.at(i), s) >= 0 })
// i < j for non-empty x
for i+1 < j {
// 0 <= i < j <= len(x.sa) && (x.at(i) <= s < x.at(j) || (s is not in x))
h := i + (j-i)/2 // i < h < j
if bytes.Compare(x.at(h), s) <= 0 {
i = h
} else { // s < x.at(h)
j = h
}
}
// i+1 == j for non-empty x
return i
} }
@ -84,12 +71,7 @@ func (x *Index) Lookup(s []byte, n int) []int {
if len(s) > 0 && n != 0 { if len(s) > 0 && n != 0 {
// find matching suffix index i // find matching suffix index i
i := x.search(s) i := x.search(s)
// x.at(i) <= s < x.at(i+1) // x.at(i-1) < s <= x.at(i)
// ignore the first suffix if it is < s
if i < len(x.sa) && bytes.Compare(x.at(i), s) < 0 {
i++
}
// collect the following suffixes with matching prefixes // collect the following suffixes with matching prefixes
for (n < 0 || len(res) < n) && i < len(x.sa) && bytes.HasPrefix(x.at(i), s) { for (n < 0 || len(res) < n) && i < len(x.sa) && bytes.HasPrefix(x.at(i), s) {