In Linux, when developing a postscript printer driver, I get the postscript file, it contains some strings like this:
5 0 obj
<</Filter[/ASCII85Decode
/LZWDecode]/Length 726>>stream
J/grZ!H>tg",&r_d#e?fg'SZ`7Df.n`+CqG$q(7C4@1>.Maep],<.+2$60G.Ek,F1;_46Q@PHaA
#cJ(HPbQ##d88(!K#-S9!Gj4q3J`[7UN(88%TJ4La+FDCph2Ob<5p0ALsi79)-"UCkeQ8#9cV[&
A)V92Z7m1-Mkra>H42YB'b#VmOMGX4X:-RgCR*6\0c1BD(TZXkDE\rrC3TPu#[rCsh*rVo<(@gS
*"Rf,3rSoP3?J]POA.FG`[r$eXOPY"9S7l)f'BnO#f).UdZ#h>lXn;b3?!ikH4b'7C!*qoDPGO?
fPN_gNA!6&mSbEul!a*A^?/42QHWdB);a!qZp#rXJR+]ip@hK/r'"$9[Ps#p3R0sghmI-eKW2+*
a;!nrC#EOh0oD?Sr@Z3.+rEXbN%5/tiIHgn+tL:ZWJJooA@sf4*&.d]alGq07?4uBqo02oCrJgs
]JB:OYNU6Ma,uS>WC@I\Z5BW]:g1qpm_EHYa6O^?fnU`hI^Q0"/"lgK!PGf^Xt6Z'^TFT$@dq>&
;u455m#'Z?_,+rh)DUa1P8?%@'$13_ZR!KQ_,<Zu*sOO%j;LV[o8*n\Lt(S,ZYqsT_?HX7bg=HE
UM:XR&l<<_UJV`r(q/^OW3h:2r"Q&)%kEIA\F(992_r`Q$l7BL[%BI\N.\jo#,.;X":*KkNZ:[-
K64:SNU&qs`O(#Ar6^<_f$gaW]Y?]c_CBFOJQDmS~>
endstream
endobj
I want to parse the string with /Filter[/ASCII85Decode /LZWDecode], my decode programm is shown below, but the result is incorrect, I want to know is my program has problem?
And should I how to parse the string above?
int Ascii85DecodeBlock( unsigned char *ascii85_p, const unsigned char *raw_p, int raw_l )
{
// ascii85_p = new unsigned char[raw_l];
int len = 0;
int count = 0;
bool processChar = false;
unsigned int _tuple = 0;
const int _asciiOffset = 33;
unsigned int pow85[] = { 85*85*85*85, 85*85*85, 85*85, 85, 1 };
unsigned char _decodedBlock[4];
for (int i = 0; i < raw_l; ++i) // char c in s)
{
unsigned char c = raw_p;
switch (c)
{
case 'z':
if (count != 0)
{
// throw new Exception("The character 'z' is invalid inside an ASCII85 block.");
}
_decodedBlock[0] = 0;
_decodedBlock[1] = 0;
_decodedBlock[2] = 0;
_decodedBlock[3] = 0;
// ms.Write(_decodedBlock, 0, _decodedBlock.Length);
for (int j = 0; j < 4; ++j)
{
ascii85_p[len++] = _decodedBlock;
}
processChar = false;
break;
case '\n': case '\r': case '\t': case '\0': case '\f': case '\b':
processChar = false;
break;
default:
if (c < '!' || c > 'u')
{
// throw new Exception("Bad character '" + c + "' found. ASCII85 only allows characters '!' to 'u'.");
}
processChar = true;
break;
}
if (processChar)
{
_tuple += ((uint)(c - _asciiOffset) * pow85[count]);
count++;
if (count == 5)
{
for (int j = 0; j < 4; j++)
{
_decodedBlock = (unsigned char)(_tuple >> (24 - (j * 8)));
}
for (int j = 0; j < 4; ++j)
{
ascii85_p[len++] = _decodedBlock;
}
_tuple = 0;
count = 0;
}
}
}
// if we have some bytes left over at the end..
if (count != 0)
{
if (count == 1)
{
// throw new Exception("The last block of ASCII85 data cannot be a single byte.");
}
count--;
_tuple += pow85[count];
for (int j = 0; j < count; j++)
{
_decodedBlock = (unsigned char)(_tuple >> (24 - (j * 8)));
}
for (int j = 0; j < count; j++)
{
ascii85_p[len++] = _decodedBlock;
}
}
return len;
}
int lzwDecode(unsigned char *lzwdata, unsigned int *raw_p, int raw_l)// 译码；
{
/*cout<<"Input num of decode:";
cin>>len;
cout<<endl;
cout<<"Input string of decode:"<<endl;
for(int j=0;j<len;j++)
{
cin>>a;
}
n=128;
cout<<endl;
cout<<"Result:"<<endl<<endl;*/
unsigned char h[2];
unsigned char p[100];
int n = 256;
cout<<Dictionary[raw_p[0]];
strcat((char*)lzwdata, (char*)Dictionary[raw_p[0]]);
strcpy((char*)p, (char*)Dictionary[raw_p[0]]);
for(int i = 1; i < raw_l; i++)
{
if(Dictionary[raw_p][0])
{
cout<<Dictionary[raw_p];
strcat((char*)lzwdata, (char*)Dictionary[raw_p]);
h[0]=Dictionary[raw_p][0];
strcpy((char*)Dictionary,strcat((char*)p,(char*)h));
strcpy((char*)p,(char*)Dictionary[raw_p]);
n++;
}
else
{
h[0]=p[0];
strcpy((char*)Dictionary,strcat((char*)p,(char*)h));
cout<<Dictionary;
strcat((char*)lzwdata, (char*)Dictionary);
strcpy((char*)p,(char*)Dictionary[raw_p]);
n++;
}
}
cout<<endl;
return strlen((char*)lzwdata);
}
AdChoices