void divide_bignum(bignum *a, bignum *b, bignum *c)
{
bignum row, tmp;
int asign, bsign, i, j;
initialize_bignum(c);
c->signbit = a->signbit * b->signbit;
asign = a->signbit;
bsign = b->signbit;
a->signbit = PLUS;
b->signbit = PLUS;
initialize_bignum(&row);
initialize_bignum(&tmp);
c->lastdigit = a->lastdigit;
for (i = a->lastdigit; i >= 0; i--) {
digit_shift(&row, 1);
row.digits[0] = a->digits[i];
c->digits[i] = 0;
while (compare_bignum(&row, b) != PLUS) {
c->digits[i]++;
subtract_bignum(&row, b, &tmp);
row = tmp;
}
}
zero_justify(c);
a->signbit = asign;
b->signbit = bsign;
}
add_bignum(bignum *a, bignum *b, bignum *c)
{
int carry; /* carry digit */
int i; /* counter */
initialize_bignum(c);
if (a->signbit == b->signbit) c->signbit = a->signbit;
else {
if (a->signbit == MINUS) {
a->signbit = PLUS;
subtract_bignum(b,a,c);
a->signbit = MINUS;
} else {
b->signbit = PLUS;
subtract_bignum(a,b,c);
b->signbit = MINUS;
}
return;
}
c->lastdigit = max(a->lastdigit,b->lastdigit)+1;
carry = 0;
for (i=0; i<=(c->lastdigit); i++) {
c->digits[i] = (char) (carry+a->digits[i]+b->digits[i]) % 10;
carry = (carry + a->digits[i] + b->digits[i]) / 10;
}
zero_justify(c);
}
void subtract_bignum(bignum *a, bignum *b, bignum *c)
{
int borrow, v, i;
if ((a->signbit == MINUS) || (b->signbit == MINUS)) {
b->signbit = -1 * b->signbit;
add_bignum(a, b, c);
b->signbit = -1 * b->signbit;
return;
}
if (compare_bignum(a, b) == PLUS) {
subtract_bignum(b, a, c);
c->signbit = MINUS;
return;
}
c->lastdigit = max(a->lastdigit, b->lastdigit);
borrow = 0;
for (i = 0; i <= c->lastdigit; i++) {
v = (a->digits[i] - borrow - b->digits[i]);
if (a->digits[i] > 0)
borrow = 0;
if (v < 0) {
v = v + 10;
borrow = 1;
}
c->digits[i] = (char) v % 10;
}
zero_justify(c);
}
void multiply_bignum(bignum *a, bignum *b, bignum *c)
{
bignum row, tmp;
int i, j;
initialize_bignum(c);
row = *a;
for (i = 0; i <= b->lastdigit; i++) {
for (j = 1; j <= b->digits[i]; j++) {
add_bignum(c, &row, &tmp);
*c = tmp;
}
digit_shift(&row, 1);
}
c->signbit = a->signbit * b->signbit;
zero_justify(c);
}
/** Subtracts big numbers; i.e. c = a - b */
void subtract_bignum( bignum* a, bignum* b, bignum* c )
{
int borrow; /* has anything been borrowed? */
int v; /* placeholder digit */
int i; /* counter */
initialize_bignum( c );
if( ( a->signbit == MINUS ) || ( b->signbit == MINUS ) )
{
b->signbit = -1 * b->signbit;
add_bignum( a, b, c );
b->signbit = -1 * b->signbit;
return;
}
if( compare_bignum( a, b ) == PLUS )
{
subtract_bignum( b, a, c );
c->signbit = MINUS;
return;
}
c->lastdigit = max( a->lastdigit, b->lastdigit );
borrow = 0;
for( i = 0; i <= ( c->lastdigit ); i++ )
{
v = ( a->digits[ i ] - borrow - b->digits[ i ] );
if( a->digits[ i ] > 0)
{
borrow = 0;
}
if( v < 0 )
{
v = v + 10;
borrow = 1;
}
c->digits[ i ] = ( char ) v % 10;
}
zero_justify( c );
}
void multiply_bignum(bignum *a, bignum *b, bignum *c) {
bignum row; /* represent shifted row */
bignum tmp; /* placeholder bignum */
int i,j; /* counters */
initialize_bignum(c);
row = *a;
for(i = 0; i <= b->lastdigit; i++) {
for(j = 1; j <= b->digits[i]; j++) {
add_bignum(c,&row,&tmp);
*c = tmp;
}
digit_shift(&row,1);
}
c->signbit = a->signbit * b->signbit;
zero_justify(c);
}
void divide_bignum(bignum *a, bignum *b, bignum *c) {
bignum row; /* represent shifted row */
bignum tmp; /* placeholder bignum */
int asign, bsign; /* temporary signs */
int i; /* counters */
initialize_bignum(c);
c->signbit = a->signbit * b->signbit;
asign = a->signbit;
bsign = b->signbit;
a->signbit = PLUS;
b->signbit = PLUS;
initialize_bignum(&row);
initialize_bignum(&tmp);
c->lastdigit = a->lastdigit;
for(i = a->lastdigit; i >= 0; i--) {
digit_shift(&row,1);
row.digits[0] = a->digits[i];
c->digits[i] = 0;
while(compare_bignum(&row,b) != PLUS) {
c->digits[i] ++;
subtract_bignum(&row,b,&tmp);
row = tmp;
}
}
zero_justify(c);
a->signbit = asign;
b->signbit = bsign;
}
