void BigInt_PowerModulus(BigInt n, BigInt exp, BigInt modulus, BigInt answer)
{
DIGIT *eptr, *eend, emask;
BigInt p, temp, r;
r=BigInt_Zero();
/* If n is negative and the exponent is odd, the answer will be negative. */
int neg=(n->negative && (exp->digits[0]&0x01));
p=BigInt_Create();
temp=BigInt_Create();
if(modulus) r=BigInt_Create();
BigInt_Copy(p, n);
p->negative=0;
BigInt_Set(answer, 1);
/* Continue this loop while the exponent is not zero */
eptr=exp->digits;
eend=eptr+exp->length;
emask=0x01;
while(eptr<eend)
{
/* If e is odd, multiply the answer by p */
if((*eptr) & emask)
{
BigInt_Copy(temp, answer);
BigInt_Multiply(temp, p, answer);
if(modulus)
{
BigInt_Modulus(answer, modulus, r);
BigInt_Copy(answer, r);
}
}
/* Now square p (mod modulus, if supplied) */
BigInt_Multiply(p, p, temp);
if(modulus) BigInt_Modulus(temp, modulus, p);
else BigInt_Copy(p, temp);
/* Shift e right by one bit */
emask<<=1;
if(emask==0)
{
++eptr;
emask=0x01;
}
}
answer->negative=neg;
if(modulus) BigInt_Destroy(r);
BigInt_Destroy(temp);
BigInt_Destroy(p);
}
char* EncodeShortV3(unsigned char* keybytes, int keylength, bool level10)
{
char* cc;
char* shortv3digits=(char*)"0123456789ABCDEFGHJKMNPQRTUVWXYZ";
static char retval[512]="";
int level=0;
int dcount;
int nn;
if(level10)
level=29;
strcpy(retval, "");
BigInt n=BigInt_Create();
BigInt t1=BigInt_Create();
BigInt t2=BigInt_Create();
if(level==29)
BigInt_Set(n, 1);
for(int x=0; x<keylength; ++x)
{
BigInt_Shift(n, 8, t1);
BigInt_SetU(t2, keybytes[x]);
BigInt_Add(t1, t2, n);
}
cc=retval;
dcount=6;
while(BigInt_Compare(n, BigInt_Zero())!=0)
{
BigInt_SetU(t2, 32);
BigInt_Modulus(n, t2, t1);
nn=BigInt_Get(t1);
BigInt_Shift(n, -5, t2);
BigInt_Copy(n, t2);
if(level==29)
{
*cc++=shortv3digits[nn];
if(--dcount==0)
{
dcount=6;
*cc++='-';
}
}
else
{
if(BigInt_Compare(n, BigInt_Zero())==0)
{
if(nn<16)
{
*cc++=shortv3digits[nn+16];
--dcount;
}
else
{
*cc++=shortv3digits[nn];
if(--dcount==0)
{
dcount=6;
*cc++='-';
}
*cc++=shortv3digits[16];
--dcount;
}
}
else
{
*cc++=shortv3digits[nn];
if(--dcount==0)
{
dcount=6;
*cc++='-';
}
}
}
}
if(level==29)
{
*cc++='1';
--dcount;
}
while(dcount-->0)
*cc++='0';
*cc=0;
mystrrev(retval);
BigInt_Destroy(t2);
BigInt_Destroy(t1);
BigInt_Destroy(n);
return retval;
}
