From 554fd8c5195424bdbcabf5de30fdc183aba391bd Mon Sep 17 00:00:00 2001 From: upstream source tree Date: Sun, 15 Mar 2015 20:14:05 -0400 Subject: obtained gcc-4.6.4.tar.bz2 from upstream website; verified gcc-4.6.4.tar.bz2.sig; imported gcc-4.6.4 source tree from verified upstream tarball. downloading a git-generated archive based on the 'upstream' tag should provide you with a source tree that is binary identical to the one extracted from the above tarball. if you have obtained the source via the command 'git clone', however, do note that line-endings of files in your working directory might differ from line-endings of the respective files in the upstream repository. --- libgo/go/index/suffixarray/qsufsort.go | 164 +++++++++++++++++++++++++++++++++ 1 file changed, 164 insertions(+) create mode 100644 libgo/go/index/suffixarray/qsufsort.go (limited to 'libgo/go/index/suffixarray/qsufsort.go') diff --git a/libgo/go/index/suffixarray/qsufsort.go b/libgo/go/index/suffixarray/qsufsort.go new file mode 100644 index 000000000..0e6894a8b --- /dev/null +++ b/libgo/go/index/suffixarray/qsufsort.go @@ -0,0 +1,164 @@ +// Copyright 2011 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// This algorithm is based on "Faster Suffix Sorting" +// by N. Jesper Larsson and Kunihiko Sadakane +// paper: http://www.larsson.dogma.net/ssrev-tr.pdf +// code: http://www.larsson.dogma.net/qsufsort.c + +// This algorithm computes the suffix array sa by computing its inverse. +// Consecutive groups of suffixes in sa are labeled as sorted groups or +// unsorted groups. For a given pass of the sorter, all suffixes are ordered +// up to their first h characters, and sa is h-ordered. Suffixes in their +// final positions and unambiguouly sorted in h-order are in a sorted group. +// Consecutive groups of suffixes with identical first h characters are an +// unsorted group. In each pass of the algorithm, unsorted groups are sorted +// according to the group number of their following suffix. + +// In the implementation, if sa[i] is negative, it indicates that i is +// the first element of a sorted group of length -sa[i], and can be skipped. +// An unsorted group sa[i:k] is given the group number of the index of its +// last element, k-1. The group numbers are stored in the inverse slice (inv), +// and when all groups are sorted, this slice is the inverse suffix array. + +package suffixarray + +import "sort" + +func qsufsort(data []byte) []int { + // initial sorting by first byte of suffix + sa := sortedByFirstByte(data) + if len(sa) < 2 { + return sa + } + // initialize the group lookup table + // this becomes the inverse of the suffix array when all groups are sorted + inv := initGroups(sa, data) + + // the index starts 1-ordered + sufSortable := &suffixSortable{sa, inv, 1} + + for sa[0] > -len(sa) { // until all suffixes are one big sorted group + // The suffixes are h-ordered, make them 2*h-ordered + pi := 0 // pi is first position of first group + sl := 0 // sl is negated length of sorted groups + for pi < len(sa) { + if s := sa[pi]; s < 0 { // if pi starts sorted group + pi -= s // skip over sorted group + sl += s // add negated length to sl + } else { // if pi starts unsorted group + if sl != 0 { + sa[pi+sl] = sl // combine sorted groups before pi + sl = 0 + } + pk := inv[s] + 1 // pk-1 is last position of unsorted group + sufSortable.sa = sa[pi:pk] + sort.Sort(sufSortable) + sufSortable.updateGroups(pi) + pi = pk // next group + } + } + if sl != 0 { // if the array ends with a sorted group + sa[pi+sl] = sl // combine sorted groups at end of sa + } + + sufSortable.h *= 2 // double sorted depth + } + + for i := range sa { // reconstruct suffix array from inverse + sa[inv[i]] = i + } + return sa +} + + +func sortedByFirstByte(data []byte) []int { + // total byte counts + var count [256]int + for _, b := range data { + count[b]++ + } + // make count[b] equal index of first occurence of b in sorted array + sum := 0 + for b := range count { + count[b], sum = sum, count[b]+sum + } + // iterate through bytes, placing index into the correct spot in sa + sa := make([]int, len(data)) + for i, b := range data { + sa[count[b]] = i + count[b]++ + } + return sa +} + + +func initGroups(sa []int, data []byte) []int { + // label contiguous same-letter groups with the same group number + inv := make([]int, len(data)) + prevGroup := len(sa) - 1 + groupByte := data[sa[prevGroup]] + for i := len(sa) - 1; i >= 0; i-- { + if b := data[sa[i]]; b < groupByte { + if prevGroup == i+1 { + sa[i+1] = -1 + } + groupByte = b + prevGroup = i + } + inv[sa[i]] = prevGroup + if prevGroup == 0 { + sa[0] = -1 + } + } + // Separate out the final suffix to the start of its group. + // This is necessary to ensure the suffix "a" is before "aba" + // when using a potentially unstable sort. + lastByte := data[len(data)-1] + s := -1 + for i := range sa { + if sa[i] >= 0 { + if data[sa[i]] == lastByte && s == -1 { + s = i + } + if sa[i] == len(sa)-1 { + sa[i], sa[s] = sa[s], sa[i] + inv[sa[s]] = s + sa[s] = -1 // mark it as an isolated sorted group + break + } + } + } + return inv +} + + +type suffixSortable struct { + sa []int + inv []int + h int +} + +func (x *suffixSortable) Len() int { return len(x.sa) } +func (x *suffixSortable) Less(i, j int) bool { return x.inv[x.sa[i]+x.h] < x.inv[x.sa[j]+x.h] } +func (x *suffixSortable) Swap(i, j int) { x.sa[i], x.sa[j] = x.sa[j], x.sa[i] } + + +func (x *suffixSortable) updateGroups(offset int) { + prev := len(x.sa) - 1 + group := x.inv[x.sa[prev]+x.h] + for i := prev; i >= 0; i-- { + if g := x.inv[x.sa[i]+x.h]; g < group { + if prev == i+1 { // previous group had size 1 and is thus sorted + x.sa[i+1] = -1 + } + group = g + prev = i + } + x.inv[x.sa[i]] = prev + offset + if prev == 0 { // first group has size 1 and is thus sorted + x.sa[0] = -1 + } + } +} -- cgit v1.2.3