/** Get value of big integer.
*
* Allows to obtain the value of big integer, provided that it fits
* into a small integer.
*
* @param bigint Bigint to obtain value from.
* @param dval Place to store value.
* @return EOK on success, ELIMIT if bigint is too big to fit
* to @a dval.
*/
int bigint_get_value_int(bigint_t *bigint, int *dval)
{
bigint_t vval, diff;
size_t idx;
int val;
bool_t zf;
#ifdef DEBUG_BIGINT_TRACE
printf("Get int value of bigint.\n");
#endif
val = 0;
for (idx = 0; idx < bigint->length; ++idx) {
val = val * BIGINT_BASE + bigint->digit[idx];
}
if (bigint->negative)
val = - val;
/* If the value did not fit @c val now contains garbage. Verify. */
bigint_init(&vval, val);
bigint_sub(bigint, &vval, &diff);
zf = bigint_is_zero(&diff);
bigint_destroy(&vval);
bigint_destroy(&diff);
/* If the difference is not zero, the verification failed. */
if (zf != b_true)
return EINVAL;
*dval = val;
return EOK;
}
/* Return 1 if the current cell is 0 and 0 otherwise */
int is_zero(Memory *mem) {
void *cell;
/* memory leak, return 0 even though the program is about to die */
if(!(cell = get_cell(mem))) return 0;
if(wrap) return *(unsigned char *)cell == 0;
else return bigint_is_zero(cell);
}
/**
* Perform modular exponentiation of big integers
*
* @v base0 Element 0 of big integer base
* @v modulus0 Element 0 of big integer modulus
* @v exponent0 Element 0 of big integer exponent
* @v result0 Element 0 of big integer to hold result
* @v size Number of elements in base, modulus, and result
* @v exponent_size Number of elements in exponent
* @v tmp Temporary working space
*/
void bigint_mod_exp_raw ( const bigint_element_t *base0,
const bigint_element_t *modulus0,
const bigint_element_t *exponent0,
bigint_element_t *result0,
unsigned int size, unsigned int exponent_size,
void *tmp ) {
const bigint_t ( size ) __attribute__ (( may_alias )) *base =
( ( const void * ) base0 );
const bigint_t ( size ) __attribute__ (( may_alias )) *modulus =
( ( const void * ) modulus0 );
const bigint_t ( exponent_size ) __attribute__ (( may_alias ))
*exponent = ( ( const void * ) exponent0 );
bigint_t ( size ) __attribute__ (( may_alias )) *result =
( ( void * ) result0 );
size_t mod_multiply_len = bigint_mod_multiply_tmp_len ( modulus );
struct {
bigint_t ( size ) base;
bigint_t ( exponent_size ) exponent;
uint8_t mod_multiply[mod_multiply_len];
} *temp = tmp;
static const uint8_t start[1] = { 0x01 };
memcpy ( &temp->base, base, sizeof ( temp->base ) );
memcpy ( &temp->exponent, exponent, sizeof ( temp->exponent ) );
bigint_init ( result, start, sizeof ( start ) );
while ( ! bigint_is_zero ( &temp->exponent ) ) {
if ( bigint_bit_is_set ( &temp->exponent, 0 ) ) {
bigint_mod_multiply ( result, &temp->base, modulus,
result, temp->mod_multiply );
}
bigint_ror ( &temp->exponent );
bigint_mod_multiply ( &temp->base, &temp->base, modulus,
&temp->base, temp->mod_multiply );
}
}
/** Convert bigint to string.
*
* @param bigint Bigint to convert.
* @param dptr Place to store pointer to new string.
*/
void bigint_get_as_string(bigint_t *bigint, char **dptr)
{
static const char digits[] = { '0', '1', '2', '3', '4', '5', '6',
'7', '8', '9' };
bigint_t val, tmp;
bigint_word_t rem;
size_t nchars;
char *str;
size_t idx;
#ifdef DEBUG_BIGINT_TRACE
printf("Convert bigint to string.\n");
#endif
static_assert(BIGINT_BASE >= 10);
/* Compute number of characters. */
nchars = 0;
if (bigint_is_zero(bigint) || bigint->negative)
nchars += 1; /* '0' or '-' */
bigint_clone(bigint, &val);
while (bigint_is_zero(&val) != b_true) {
bigint_div_digit(&val, 10, &tmp, &rem);
bigint_destroy(&val);
bigint_shallow_copy(&tmp, &val);
nchars += 1;
}
bigint_destroy(&val);
/* Store characters to array. */
str = malloc(nchars * sizeof(char) + 1);
if (str == NULL) {
printf("Memory allocation failed.\n");
exit(1);
}
if (bigint_is_zero(bigint)) {
str[0] = '0';
} else if (bigint->negative) {
str[0] = '-';
}
idx = 1;
bigint_clone(bigint, &val);
while (bigint_is_zero(&val) != b_true) {
bigint_div_digit(&val, 10, &tmp, &rem);
bigint_destroy(&val);
bigint_shallow_copy(&tmp, &val);
str[nchars - idx] = digits[(int) rem];
++idx;
}
bigint_destroy(&val);
str[nchars] = '\0';
*dptr = str;
}
