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Fix split() pivoting to avoid stack overflow from Quicksort worst case. #12

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Fix split() pivoting to avoid stack overflow from Quicksort worst case. #12

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26 changes: 21 additions & 5 deletions bsdiff.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@
* All rights reserved
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted providing that the following conditions
* modification, are permitted providing that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
Expand All @@ -31,10 +31,13 @@
#include <string.h>

#define MIN(x,y) (((x)<(y)) ? (x) : (y))
#define MEDIAN3(a,b,c) (((a)<(b)) ? \
((b)<(c) ? (b) : ((a)<(c) ? (c) : (a))) : \
((b)>(c) ? (b) : ((a)>(c) ? (c) : (a))))

static void split(int64_t *I,int64_t *V,int64_t start,int64_t len,int64_t h)
{
int64_t i,j,k,x,tmp,jj,kk;
int64_t i,j,k,x,y,z,tmp,jj,kk;

if(len<16) {
for(k=start;k<start+len;k+=j) {
Expand All @@ -55,7 +58,20 @@ static void split(int64_t *I,int64_t *V,int64_t start,int64_t len,int64_t h)
return;
};

x=V[I[start+len/2]+h];
/* Select pivot, algorithm by Bentley & McIlroy */
j=start+len/2;
k=start+len-1;
x=V[I[j]+h];
y=V[I[start]+h];
z=V[I[k]+h];
if(len>40) { /* Big array: Pseudomedian of 9 */
tmp=len/8;
x=MEDIAN3(x,V[I[j-tmp]+h],V[I[j+tmp]+h]);
y=MEDIAN3(y,V[I[start+tmp]+h],V[I[start+tmp+tmp]+h]);
z=MEDIAN3(z,V[I[k-tmp]+h],V[I[k-tmp-tmp]+h]);
}; /* Else medium array: Pseudomedian of 3 */
x=MEDIAN3(x,y,z);

jj=0;kk=0;
for(i=start;i<start+len;i++) {
if(V[I[i]+h]<x) jj++;
Expand Down Expand Up @@ -252,7 +268,7 @@ static int bsdiff_internal(const struct bsdiff_request req)
(req.old[scsc+lastoffset] == req.new[scsc]))
oldscore++;

if(((len==oldscore) && (len!=0)) ||
if(((len==oldscore) && (len!=0)) ||
(len>oldscore+8)) break;

if((scan+lastoffset<req.oldsize) &&
Expand Down Expand Up @@ -414,7 +430,7 @@ int main(int argc,char *argv[])
if ((pf = fopen(argv[3], "w")) == NULL)
err(1, "%s", argv[3]);

/* Write header (signature+newsize)*/
/* Write header (signature+newsize) */
offtout(newsize, buf);
if (fwrite("ENDSLEY/BSDIFF43", 16, 1, pf) != 1 ||
fwrite(buf, sizeof(buf), 1, pf) != 1)
Expand Down