作者:Ericke2702932972 | 来源:互联网 | 2023-05-18 17:40
最近在研究差分算法,下载了一个开源的bsdiff4.3,用的后缀算法,但不是罗神的倍增算法,是LS算法,但代码晦涩难懂,请大侠们分析下,staticvoidsplit(off_t*I,of
最近在研究差分算法,下载了一个开源的bsdiff 4.3,用的后缀算法,但不是罗神的倍增算法,是LS算法,但代码晦涩难懂,请大侠们分析下,
static void split(off_t *I,off_t *V,off_t start,off_t len,off_t h)
{
off_t i,j,k,x,tmp,jj,kk;
if(len<16) {
for(k=start;k
j=1;x=V[I[k]+h];
for(i=1;k+i if(V[I[k+i]+h] x=V[I[k+i]+h];
j=0;
};
if(V[I[k+i]+h]==x) {
tmp=I[k+j];I[k+j]=I[k+i];I[k+i]=tmp;
j++;
};
};
for(i=0;i if(j==1) I[k]=-1;
};
return;
};
x=V[I[start+len/2]+h];
jj=0;kk=0;
for(i=start;i if(V[I[i]+h] if(V[I[i]+h]==x) kk++;
};
jj+=start;kk+=jj;
i=start;j=0;k=0;
while(i if(V[I[i]+h] i++;
} else if(V[I[i]+h]==x) {
tmp=I[i];I[i]=I[jj+j];I[jj+j]=tmp;
j++;
} else {
tmp=I[i];I[i]=I[kk+k];I[kk+k]=tmp;
k++;
};
};
while(jj+j if(V[I[jj+j]+h]==x) {
j++;
} else {
tmp=I[jj+j];I[jj+j]=I[kk+k];I[kk+k]=tmp;
k++;
};
};
if(jj>start) split(I,V,start,jj-start,h);
for(i=0;i if(jj==kk-1) I[jj]=-1;
if(start+len>kk) split(I,V,kk,start+len-kk,h);
}
static void qsufsort(off_t *I,off_t *V,u_char *old,off_t oldsize)
{
off_t buckets[256];
off_t i,h,len;
for(i=0;i<256;i++) buckets[i]=0;
for(i=0;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 I[0]=oldsize;
for(i=0;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 if(I[i]<0) {
len-=I[i];
i-=I[i];
} else {
if(len) I[i-len]=-len;
len=V[I[i]]+1-i;
split(I,V,i,len,h);
i+=len;
len=0;
};
};
if(len) I[i-len]=-len;
};
for(i=0;i }
static off_t matchlen(u_char *old,off_t oldsize,u_char *new,off_t newsize)
{
off_t i;
for(i=0;(i if(old[i]!=new[i]) break;
return i;
}
static off_t search(off_t *I,u_char *old,off_t oldsize,
u_char *new,off_t newsize,off_t st,off_t en,off_t *pos)
{
off_t x,y;
if(en-st<2) {
x=matchlen(old+I[st],oldsize-I[st],new,newsize);
y=matchlen(old+I[en],oldsize-I[en],new,newsize);
if(x>y) {
*pos=I[st];
return x;
} else {
*pos=I[en];
return y;
}
};
x=st+(en-st)/2;
if(memcmp(old+I[x],new,MIN(oldsize-I[x],newsize))<0) {
return search(I,old,oldsize,new,newsize,x,en,pos);
} else {
return search(I,old,oldsize,new,newsize,st,x,pos);
};
}
static void offtout(off_t x,u_char *buf)
{
off_t y;
if(x<0) y=-x; else y=x;
buf[0]=y%256;y-=buf[0];
y=y/256;buf[1]=y%256;y-=buf[1];
y=y/256;buf[2]=y%256;y-=buf[2];
y=y/256;buf[3]=y%256;y-=buf[3];
y=y/256;buf[4]=y%256;y-=buf[4];
y=y/256;buf[5]=y%256;y-=buf[5];
y=y/256;buf[6]=y%256;y-=buf[6];
y=y/256;buf[7]=y%256;
if(x<0) buf[7]|=0x80;
}
int main(int argc,char *argv[])
{
...............
qsufsort(I,V,old,oldsize);//这个应该是LS算法,但是没有看懂
free(V);
/* Allocate newsize+1 bytes instead of newsize bytes to ensure
that we never try to malloc(0) and get a NULL pointer */
if(((fd=open(argv[2],O_RDONLY,0))<0) ||
((newsize=lseek(fd,0,SEEK_END))==-1) ||
((new=malloc(newsize+1))==NULL) ||
(lseek(fd,0,SEEK_SET)!=0) ||
(read(fd,new,newsize)!=newsize) ||
(close(fd)==-1)) err(1,"%s",argv[2]);
if(((db=malloc(newsize+1))==NULL) ||
((eb=malloc(newsize+1))==NULL)) err(1,NULL);
dblen=0;
eblen=0;
/* Create the patch file */
if ((pf = fopen(argv[3], "w")) == NULL)
err(1, "%s", argv[3]);
/* Header is
0 8 "BSDIFF40"
8 8 length of bzip2ed ctrl block
16 8 length of bzip2ed diff block
24 8 length of new file */
/* File is
0 32 Header
32 ?? Bzip2ed ctrl block
?? ?? Bzip2ed diff block
?? ?? Bzip2ed extra block */
memcpy(header,"BSDIFF40",8);
offtout(0, header + 8);
offtout(0, header + 16);
offtout(newsize, header + 24);
if (fwrite(header, 32, 1, pf) != 1)
err(1, "fwrite(%s)", argv[3]);
/* Compute the differences, writing ctrl as we go */
if ((pfbz2 = BZ2_bzWriteOpen(&bz2err, pf, 9, 0, 0)) == NULL)
errx(1, "BZ2_bzWriteOpen, bz2err = %d", bz2err);
scan=0;len=0;
lastscan=0;lastpos=0;lastoffset=0;
while(scan oldscore=0;
for(scsc=scan+=len;scan len=search(I,old,oldsize,new+scan,newsize-scan,
0,oldsize,&pos);
for(;scsc if((scsc+lastoffset (old[scsc+lastoffset] == new[scsc]))
oldscore++;
if(((len==oldscore) && (len!=0)) ||
(len>oldscore+8)) break;
if((scan+lastoffset (old[scan+lastoffset] == new[scan]))
oldscore--;
};
if((len!=oldscore) || (scan==newsize)) {
s=0;Sf=0;lenf=0;
for(i=0;(lastscan+i if(old[lastpos+i]==new[lastscan+i]) s++;
i++;
if(s*2-i>Sf*2-lenf) { Sf=s; lenf=i; };
};
lenb=0;
if(scan s=0;Sb=0;
for(i=1;(scan>=lastscan+i)&&(pos>=i);i++) {
if(old[pos-i]==new[scan-i]) s++;
if(s*2-i>Sb*2-lenb) { Sb=s; lenb=i; };
};
};
if(lastscan+lenf>scan-lenb) {
overlap=(lastscan+lenf)-(scan-lenb);
s=0;Ss=0;lens=0;
for(i=0;i if(new[lastscan+lenf-overlap+i]==
old[lastpos+lenf-overlap+i]) s++;
if(new[scan-lenb+i]==
old[pos-lenb+i]) s--;
if(s>Ss) { Ss=s; lens=i+1; };
};
lenf+=lens-overlap;
lenb-=lens;
};
for(i=0;i db[dblen+i]=new[lastscan+i]-old[lastpos+i];
for(i=0;i<(scan-lenb)-(lastscan+lenf);i++)
eb[eblen+i]=new[lastscan+lenf+i];
dblen+=lenf;
eblen+=(scan-lenb)-(lastscan+lenf);
offtout(lenf,buf);
BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
if (bz2err != BZ_OK)
errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
offtout((scan-lenb)-(lastscan+lenf),buf);
BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
if (bz2err != BZ_OK)
errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
offtout((pos-lenb)-(lastpos+lenf),buf);
BZ2_bzWrite(&bz2err, pfbz2, buf, 8);
if (bz2err != BZ_OK)
errx(1, "BZ2_bzWrite, bz2err = %d", bz2err);
lastscan=scan-lenb;
lastpos=pos-lenb;
lastoffset=pos-scan;
};
};
................
}
大侠帮忙看看哈,高分相送!
5 个解决方案
其中的BZ_bzWrite等压缩函数,可以不管,这些函数是用bzip2压缩算法的压缩接口