Index: courgette/third_party/qsufsort.h |
diff --git a/courgette/third_party/qsufsort.h b/courgette/third_party/qsufsort.h |
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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 - Extract 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> |
- 2016-04-27 - Change split() to use Bentley & McIlroy's pivot selection |
- algorithm, which QSufSort originally used. Reference: |
- http://www.larsson.dogma.net/qsufsort.c |
- --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. |
- |
-namespace { |
- |
-template <typename T> T median3(const T& a, const T& b, const T& c) { |
- if (a < b) |
- return b < c ? b : (a < c ? c : a); |
- return b > c ? b : (a > c ? c : a); |
-} |
- |
-} // namespace |
- |
-template <typename T> void split(T I, T V, int start, int end, int h) { |
- // For small interval, apply selection sort. |
- if (end - start < 16) { |
- 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; |
- } |
- |
- // Select pivot, algorithm by Bentley & McIlroy. |
- int n = end - start; |
- int mid = start + (n >> 1); |
- int pivot = V[I[mid] + h]; |
- int p1 = V[I[start] + h]; |
- int p2 = V[I[end - 1] + h]; |
- if (n > 40) { // Big array: Pseudomedian of 9. |
- int s = n >> 3; |
- pivot = median3(pivot, V[I[mid - s] + h], V[I[mid + s] + h]); |
- p1 = median3(p1, V[I[start + s] + h], V[I[start + s + s] + h]); |
- p2 = median3(p2, V[I[end - 1 - s] + h], V[I[end - 1 - s - s] + h]); |
- } // Else medium array: Pseudomedian of 3. |
- pivot = median3(pivot, p1, p2); |
- |
- // 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 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 |