void vli_mmod_fast_secp256r1()

in ext/tinycrypt/src/ecc.c [521:620]

• 81 lines of code
• 5 McCabe index (conditional complexity)

void vli_mmod_fast_secp256r1(unsigned int *result, unsigned int*product)
{
	unsigned int tmp[NUM_ECC_WORDS];
	int carry;

	/* t */
	uECC_vli_set(result, product, NUM_ECC_WORDS);

	/* s1 */
	tmp[0] = tmp[1] = tmp[2] = 0;
	tmp[3] = product[11];
	tmp[4] = product[12];
	tmp[5] = product[13];
	tmp[6] = product[14];
	tmp[7] = product[15];
	carry = uECC_vli_add(tmp, tmp, tmp, NUM_ECC_WORDS);
	carry += uECC_vli_add(result, result, tmp, NUM_ECC_WORDS);

	/* s2 */
	tmp[3] = product[12];
	tmp[4] = product[13];
	tmp[5] = product[14];
	tmp[6] = product[15];
	tmp[7] = 0;
	carry += uECC_vli_add(tmp, tmp, tmp, NUM_ECC_WORDS);
	carry += uECC_vli_add(result, result, tmp, NUM_ECC_WORDS);

	/* s3 */
	tmp[0] = product[8];
	tmp[1] = product[9];
	tmp[2] = product[10];
	tmp[3] = tmp[4] = tmp[5] = 0;
	tmp[6] = product[14];
	tmp[7] = product[15];
  	carry += uECC_vli_add(result, result, tmp, NUM_ECC_WORDS);

	/* s4 */
	tmp[0] = product[9];
	tmp[1] = product[10];
	tmp[2] = product[11];
	tmp[3] = product[13];
	tmp[4] = product[14];
	tmp[5] = product[15];
	tmp[6] = product[13];
	tmp[7] = product[8];
	carry += uECC_vli_add(result, result, tmp, NUM_ECC_WORDS);

	/* d1 */
	tmp[0] = product[11];
	tmp[1] = product[12];
	tmp[2] = product[13];
	tmp[3] = tmp[4] = tmp[5] = 0;
	tmp[6] = product[8];
	tmp[7] = product[10];
	carry -= uECC_vli_sub(result, result, tmp, NUM_ECC_WORDS);

	/* d2 */
	tmp[0] = product[12];
	tmp[1] = product[13];
	tmp[2] = product[14];
	tmp[3] = product[15];
	tmp[4] = tmp[5] = 0;
	tmp[6] = product[9];
	tmp[7] = product[11];
	carry -= uECC_vli_sub(result, result, tmp, NUM_ECC_WORDS);

	/* d3 */
	tmp[0] = product[13];
	tmp[1] = product[14];
	tmp[2] = product[15];
	tmp[3] = product[8];
	tmp[4] = product[9];
	tmp[5] = product[10];
	tmp[6] = 0;
	tmp[7] = product[12];
	carry -= uECC_vli_sub(result, result, tmp, NUM_ECC_WORDS);

	/* d4 */
	tmp[0] = product[14];
	tmp[1] = product[15];
	tmp[2] = 0;
	tmp[3] = product[9];
	tmp[4] = product[10];
	tmp[5] = product[11];
	tmp[6] = 0;
	tmp[7] = product[13];
	carry -= uECC_vli_sub(result, result, tmp, NUM_ECC_WORDS);

	if (carry < 0) {
		do {
			carry += uECC_vli_add(result, result, curve_secp256r1.p, NUM_ECC_WORDS);
		}
		while (carry < 0);
	} else  {
		while (carry || 
		       uECC_vli_cmp_unsafe(curve_secp256r1.p, result, NUM_ECC_WORDS) != 1) {
			carry -= uECC_vli_sub(result, result, curve_secp256r1.p, NUM_ECC_WORDS);
		}
	}
}