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/*
qsufsort.h -- Suffix array generation.
Copyright 2003 Colin Percival
For the terms under which this work may be distributed, please see
the adjoining file "LICENSE".
ChangeLog:
2005-05-05 - Use the modified header struct from bspatch.h; use 32-bit
values throughout.
--Benjamin Smedberg <benjamin@smedbergs.us>
2010-05-26 - Use a paged array for V and I. The address space may be too
fragmented for these big arrays to be contiguous.
--Stephen Adams <sra@chromium.org>
2015-08-03 - Extrat qsufsort to a separate file as template.
--Samuel Huang <huangs@chromium.org>
2015-08-19 - Optimize split() and search(), add comments.
--Samuel Huang <huangs@chromium.org>
*/
#include <algorithm>
#include <cstring>
namespace courgette {
namespace qsuf {
// ------------------------------------------------------------------------
//
// The following code is taken verbatim from 'bsdiff.c'. Please keep all the
// code formatting and variable names. The changes from the original are:
// (1) replacing tabs with spaces,
// (2) indentation,
// (3) using 'const',
// (4) changing the V and I parameters from int* to template <typename T>.
// (5) optimizing split() and search(); fix styles.
//
// The code appears to be a rewritten version of the suffix array algorithm
// presented in "Faster Suffix Sorting" by N. Jesper Larsson and Kunihiko
// Sadakane, special cased for bytes.
template <typename T> static void split(T I, T V, int start, int end, int h) {
// For small interval, apply selection sort.
if (end - start < 6) {
for (int i = start; i < end; ) {
int skip = 1;
int best = V[I[i] + h];
for (int j = i + 1; j < end; j++) {
int cur = V[I[j] + h];
if (best > cur) {
best = cur;
int tmp = I[i];
I[i] = I[j];
I[j] = tmp;
skip = 1;
} else if (best == cur) {
int tmp = I[i + skip];
I[i + skip] = I[j];
I[j] = tmp;
++skip;
}
}
if (skip == 1) {
V[I[i]] = i;
I[i] = -1;
} else {
for (int j = i, jend = i + skip; j < jend; j++)
V[I[j]] = jend - 1;
}
i += skip;
}
return;
}
// Split [start, end) into 3 intervals:
// [start, j) with secondary keys < pivot,
// [j, k) with secondary keys == pivot,
// [k, end) with secondary keys > pivot.
int pivot = V[I[(start + end) / 2] + h];
int j = start;
int k = end;
for (int i = start; i < k; ) {
int cur = V[I[i] + h];
if (cur < pivot) {
if (i != j) {
int tmp = I[i];
I[i] = I[j];
I[j] = tmp;
}
++i;
++j;
} else if (cur > pivot) {
--k;
int tmp = I[i];
I[i] = I[k];
I[k] = tmp;
} else {
++i;
}
}
// Recurse on the "< pivot" piece.
if (start < j)
split<T>(I, V, start, j, h);
// Update the "== pivot" piece.
if (j == k - 1) {
V[I[j]] = j;
I[j] = -1;
} else {
for (int i = j; i < k; ++i)
V[I[i]] = k - 1;
}
// Recurse on the "> pivot" piece.
if (k < end)
split<T>(I, V, k, end, h);
}
template <class T>
static void
qsufsort(T I, T V,const unsigned char *old,int oldsize)
{
int buckets[256];
int i,h,len;
for(i=0;i<256;i++) buckets[i]=0;
for(i=0;i<oldsize;i++) buckets[old[i]]++;
for(i=1;i<256;i++) buckets[i]+=buckets[i-1];
for(i=255;i>0;i--) buckets[i]=buckets[i-1];
buckets[0]=0;
for(i=0;i<oldsize;i++) I[++buckets[old[i]]]=i;
I[0]=oldsize;
for(i=0;i<oldsize;i++) V[i]=buckets[old[i]];
V[oldsize]=0;
for(i=1;i<256;i++) if(buckets[i]==buckets[i-1]+1) I[buckets[i]]=-1;
I[0]=-1;
for(h=1;I[0]!=-(oldsize+1);h+=h) {
len=0;
for(i=0;i<oldsize+1;) {
if(I[i]<0) {
len-=I[i];
i-=I[i];
} else {
if(len) I[i-len]=-len;
len=V[I[i]]+1-i;
split<T>(I,V,i,i+len,h);
i+=len;
len=0;
};
};
if(len) I[i-len]=-len;
};
for(i=0;i<oldsize+1;i++) I[V[i]]=i;
}
static int
matchlen(const unsigned char *old,int oldsize,const unsigned char *newbuf,int newsize)
{
int i;
for(i=0;(i<oldsize)&&(i<newsize);i++)
if(old[i]!=newbuf[i]) break;
return i;
}
template <class T>
static int search(T I, const unsigned char *old, int oldsize,
const unsigned char *newbuf, int newsize, int *pos) {
int lo = 0;
int hi = oldsize;
while (hi - lo >= 2) {
int mid = (lo + hi) / 2;
if(memcmp(old+I[mid],newbuf,std::min(oldsize-I[mid],newsize))<0) {
lo = mid;
} else {
hi = mid;
}
}
int x = matchlen(old + I[lo], oldsize - I[lo], newbuf, newsize);
int y = matchlen(old + I[hi], oldsize - I[hi], newbuf, newsize);
if(x > y) {
*pos = I[lo];
return x;
}
*pos = I[hi];
return y;
}
// End of 'verbatim' code.
// ------------------------------------------------------------------------
} // namespace qsuf
} // namespace courgette
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