# Multiple Precision Modular Arithmetics. Addition (Fixed)

My fix is connected with fact that is not always necessary to perform a modulo operation. For example: we have number a = 3, b = 4, modulus = 10. So, the operation would look something like that: (a + b) mod modulus = (3 + 4) mod 10 = 7 mod 10. Because 7 is lower than 10, we do not need the modulus operation. The structure: typedef size_t digit_t; typedef struct { int neg;         /* if TRUE, then negative number */ int sig_digits;  /* amount of significant (non-zero) digits */ int all_digits;  /* amount of overall digits in array */ digit_t *digits; /* pointer to first limb */ } bignum_t; The code would look something like that: /* (x + y) mod base */ void mpa_mod_add(bignum_t *res, const bignum_t *a, const bignum_t *b, const bignum_t *base) { int i = 0, c = 0; for (i = 0; i < a->all_digits; i++) { res->digits[i] = a->digits[i] + b->digits[i]; if (res->digits[i] >= base->digits[i]) res->digits[i] = res->digits[i] - base->digits[i]; } res->digits[res->all_digits] = c; }