mirror of
https://github.com/autc04/Retro68.git
synced 2024-09-10 03:54:48 +00:00
169 lines
4.8 KiB
Go
169 lines
4.8 KiB
Go
// 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 unambiguously 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: sa, inv: inv, h: 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 occurrence 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
|
|
buf []int // common scratch space
|
|
}
|
|
|
|
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) {
|
|
bounds := x.buf[0:0]
|
|
group := x.inv[x.sa[0]+x.h]
|
|
for i := 1; i < len(x.sa); i++ {
|
|
if g := x.inv[x.sa[i]+x.h]; g > group {
|
|
bounds = append(bounds, i)
|
|
group = g
|
|
}
|
|
}
|
|
bounds = append(bounds, len(x.sa))
|
|
x.buf = bounds
|
|
|
|
// update the group numberings after all new groups are determined
|
|
prev := 0
|
|
for _, b := range bounds {
|
|
for i := prev; i < b; i++ {
|
|
x.inv[x.sa[i]] = offset + b - 1
|
|
}
|
|
if b-prev == 1 {
|
|
x.sa[prev] = -1
|
|
}
|
|
prev = b
|
|
}
|
|
}
|