/** Test Function */
int main( )
{
bignum n1, n2, n3, zero;
// Instantiate string buffers for big numbers a and b
char* a = calloc( MAXDIGITS, sizeof( char ) );
char* b = calloc( MAXDIGITS, sizeof( char ) );
// Get big numbers a and b as strings
printf( "a = " );
fgets( a, MAXDIGITS, stdin );
printf( "b = " );
fgets( b, MAXDIGITS, stdin );
// Remove the newline character (if present) from string buffers
char* nl;
if( ( nl = strchr( a, '\n' ) ) != NULL ) *nl = '\0';
if( ( nl = strchr( b, '\n' ) ) != NULL ) *nl = '\0';
// Create a and b big number instances via the string buffers
string_to_bignum( a, &n1 );
string_to_bignum( b, &n2 );
// Test addition
add_bignum( &n1, &n2, &n3 );
printf( "a + b = " );
print_bignum( &n3 );
// Test comparison
int comparison = compare_bignum( &n1, &n2 );
printf( "a %s b\n", comparison == 0 ? "==" : ( comparison < 0 ? ">" : "<" ) );
// Test subtraction
subtract_bignum( &n1, &n2, &n3 );
printf( "a - b = " );
print_bignum( &n3 );
// Test multiplication
multiply_bignum( &n1, &n2, &n3 );
printf( "a * b = " );
print_bignum( &n3 );
// Test division
int_to_bignum( 0, &zero );
if( compare_bignum( &zero, &n2 ) == 0 )
{
printf( "a / b = NaN\n" );
}
else
{
divide_bignum( &n1, &n2, &n3 );
printf( "a / b = " );
print_bignum( &n3 );
}
return 0;
}
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;
}
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);
}
int main(void) {
int a,b;
bignum n1,n2,n3,zero;
while (scanf("%d %d",&a,&b) != EOF) {
printf("a = %d b = %d\n",a,b);
int_to_bignum(a,&n1);
int_to_bignum(b,&n2);
add_bignum(&n1,&n2,&n3);
printf("addition -- ");
print_bignum(&n3);
printf("compare_bignum a ? b = %d\n",compare_bignum(&n1, &n2));
subtract_bignum(&n1,&n2,&n3);
printf("subtraction -- ");
print_bignum(&n3);
multiply_bignum(&n1,&n2,&n3);
printf("multiplication -- ");
print_bignum(&n3);
int_to_bignum(0,&zero);
if(compare_bignum(&zero, &n2) == 0)
printf("division -- NaN \n");
else {
divide_bignum(&n1,&n2,&n3);
printf("division -- ");
print_bignum(&n3);
}
printf("--------------------------\n");
}
return 0;
}
/** 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 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;
}