Hello,
I'm having a pretty weird problem with a program i created,
it's going to be a RSA encrypter...
I've made a BigNum class that is able to do multiplications, additions, decreament, divisions and modulo on very large numbers...
The size of these numbers is defined by a contant (named range),
everything works fine if the range <= 5104 bytes, but for some sort of reason when i go above this number it won't work correctly anymore, i have a system("PAUSE"); at the end of my code, but it will just go past it and past some other calculations in my function main()... Lets say range=6104, than it will only show input, not output of other calculations, but if i delete the multiplication and division from the main() it will show the output of the modulo correctly!
I guess it has to do with memory/buffer overflow of some kind, but if it where a normal overflow of some sort it should also give errors using a number other than 512 ('cause at first i didn't use a constant for the size of the numbers, but just 512)...
I haven't got a clue what is wrong...
Help is very much appreciated!
Here is the code (sorry it's a bit long):
BTW: I'm using Borland C++ 5.0, but should compile using other compilers
#include <iostream>
#include <stdlib>
#include <stdio>
#include <memory>
#include <string>
const int range=5104;
char strnum[range*2+1];
class BigNum{
public:
unsigned char num[range];
int len;
BigNum(){memset(num, 0, range); len=1;}
BigNum(char*);
BigNum operator + (BigNum);
BigNum operator - (BigNum);
BigNum operator * (BigNum);
BigNum operator / (BigNum);
BigNum operator % (BigNum);
BigNum operator << (int);
bool operator < (BigNum);
char* print();
};
BigNum::BigNum(char* param){ //Convert hex input to char number array
memset(num, 0, range);
int tmp=strlen(param);
len=tmp/2;
for(int i=0;i<tmp;i++){
if((param[tmp-i-1]>=48)&&(param[tmp-i-1]<=57)){param[tmp-i-1]-=48;}
if((param[tmp-i-1]>=65)&&(param[tmp-i-1]<=70)){param[tmp-i-1]-=55;}
if((i%2)==1){num[(range-1)-i/2]|=param[tmp-i-1]<<4;}
else{num[(range-1)-i/2]=param[tmp-i-1];}
}
}
BigNum BigNum::operator + (BigNum param){
int tmpi;
unsigned char tmpc;
BigNum tmp;
memcpy(tmp.num, num, range); tmp.len=len;
for(int i=
0;i<param.
len;i++
){ if(tmp.len<i+1){tmp.len++;}
tmpc=tmp.num[(range-1)-i];
tmp.num[(range-1)-i]+=param.num[(range-1)-i];
if(tmpc>tmp.num[(range-1)-i]){
tmpi=0;
while(tmp.num[(range-1)-i-1-tmpi]==0xFF){tmp.num[(range-1)-i-1-tmpi]=0; tmpi++;}
tmp.num[(range-1)-i-1-tmpi]++;
if(tmp.len<i+2+tmpi){tmp.len++;}
}
}
return tmp;
}
BigNum BigNum::operator - (BigNum param){
int tmpi;
unsigned char tmpc;
BigNum tmp;
memcpy(tmp.num, num, range); tmp.len=len;
for(int i=
0;i<param.
len;i++
){ tmpc=tmp.num[(range-1)-i];
tmp.num[(range-1)-i]-=param.num[(range-1)-i];
if(tmpc<tmp.num[(range-1)-i]){
tmpi=0;
while(tmp.num[(range-1)-i-1-tmpi]==0x00){tmp.num[(range-1)-i-1-tmpi]=0xFF; tmpi++;}
tmp.num[(range-1)-i-1-tmpi]--;
}
for(tmpi=0;((tmpi<range)&&(tmp.num[tmpi]==0));tmpi++){}
tmp.len=range-tmpi;
}
return tmp;
}
bool BigNum::operator < (BigNum param){
int tmpi=0;
if(len<param.
len){return true;
} if(len==param.len){
while((tmpi<len)&&(num[range-len+tmpi]==param.num[range-param.len+tmpi])){tmpi++;}
if(num
[range-len+tmpi
]<param.
num[range-param.
len+tmpi
]){return true;
} }
return false;
}
BigNum BigNum::operator << (int shl){
BigNum tmp;
int tmpi;
unsigned char and, tmpc;
memcpy(tmp.num+range-len-shl/8, num+range-len, len);
tmp.len=len+shl/8;
if((shl%8)>0){
tmpi=shl%8;
and=(2<<tmpi)-1;
and<<=8-tmpi;
for(int i=0;i<tmp.len;i++){
tmpc=(tmp.num[range-tmp.len+i]&and)>>8-tmpi;
tmp.num[range-tmp.len+i]<<=tmpi;
tmp.num[(range-1)-tmp.len+i]|=tmpc;
}
if(tmp.num[(range-1)-tmp.len]>0){tmp.len++;}
}
return tmp;
}
BigNum BigNum::operator * (BigNum param){
BigNum tmp, out;
memcpy(tmp.num, num, range); tmp.len=len;
for(int i=
0;i<param.
len;i++
){ for(int ix=0;ix<8;ix++){
if((param.num[(range-1)-i]&1)==1){
out=out+(tmp<<(i*8+ix));
}
param.num[(range-1)-i]>>=1;
}
}
for(int i=0;((i<range)&&(out.num[i]==0));i++){out.len=(range-1)-i;}
return out;
}
BigNum BigNum::operator / (BigNum param){
int tmpi;
BigNum tmp, out, one=BigNum("01");
memcpy(tmp.num, num, range); tmp.len=len;
if(tmp<param
){return BigNum
("00");
}
while(param<tmp){
tmpi=0;
while((param<<tmpi)<tmp){tmpi++;}
if(tmpi==0){break;}
tmpi--;
tmp=tmp-(param<<tmpi);
out=out+(one<<tmpi);
}
out=out+one;
tmp=tmp-param;
}
return out;
}
BigNum BigNum::operator % (BigNum param){
int tmpi;
BigNum tmp, out, one=BigNum("01");
memcpy(tmp.num, num, range); tmp.len=len;
if(tmp<param
){return BigNum
("00");
}
while(param<tmp){
tmpi=0;
while((param<<tmpi)<tmp){tmpi++;}
if(tmpi==0){break;}
tmpi--;
tmp=tmp-(param<<tmpi);
out=out+(one<<tmpi);
}
out=out+one;
tmp=tmp-param;
}
return tmp;
}
char* BigNum::print(){
int tmp=0;
char *hex="0123456789ABCDEF";
for(int i=0;i<len;i++){
strnum[tmp]=hex[(num[range-len+i]&0xF0)>>4];
strnum[tmp+1]=hex[(num[range-len+i]&0x0F)];
tmp+=2;
}
strnum[tmp]=0;
return strnum;
}
int main(){
BigNum tmp("123456789ABCDEF7");
BigNum test("3F12");
BigNum c;
cout << "----INPUT:----\n";
printf("A:%s: %d Bytes\n", tmp.print(), tmp.len);
printf("B:%s: %d Bytes\n--------------\n\n", test.print(), test.len);
c=tmp*test;
printf("--MULTIPLY(A*B)--\n%s\n%d Bytes\n\n", c.print(), c.len);
c=tmp/test;
printf("--DIVIDE(A/B)--\n%s\n%d Bytes\n\n", c.print(), c.len);
c=tmp%test;
printf("--MODULO(A MOD B)--\n%s\n%d Bytes\n", c.print(), c.len);
system("PAUSE");
return 0;
}
Unsolved 
