Language: C
Label: safe
CWE: CWE-190 \u2014 Integer Overflow or Wraparound
The product performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control.

Code:
void fp2_exp_cyc_sim(fp2_t e, const fp2_t a, const bn_t b, const fp2_t c, const bn_t d) {
	int n0, n1;
	int8_t naf0[RLC_FP_BITS + 1], naf1[RLC_FP_BITS + 1], *_k, *_m;
	fp2_t r, t0[1 << (EP_WIDTH - 2)];
	fp2_t s, t1[1 << (EP_WIDTH - 2)];
	size_t l, l0, l1;

	if (bn_is_zero(b)) {
		return fp2_exp_cyc(e, c, d);
	}

	if (bn_is_zero(d)) {
		return fp2_exp_cyc(e, a, b);
	}

	fp2_null(r);
	fp2_null(s);

	RLC_TRY {
		fp2_new(r);
		fp2_new(s);
		for (int i = 0; i < (1 << (FP_WIDTH - 2)); i ++) {
			fp2_null(t0[i]);
			fp2_null(t1[i]);
			fp2_new(t0[i]);
			fp2_new(t1[i]);
		}

#if FP_WIDTH > 2
		fp2_sqr(t0[0], a);
		fp2_mul(t0[1], t0[0], a);
		for (int i = 2; i < (1 << (FP_WIDTH - 2)); i++) {
			fp2_mul(t0[i], t0[i - 1], t0[0]);
		}

		fp2_sqr(t1[0], c);
		fp2_mul(t1[1], t1[0], c);
		for (int i = 2; i < (1 << (FP_WIDTH - 2)); i++) {
			fp2_mul(t1[i], t1[i - 1], t1[0]);
		}
#endif
		fp2_copy(t0[0], a);
		fp2_copy(t1[0], c);

		l0 = l1 = RLC_FP_BITS + 1;
		bn_rec_naf(naf0, &l0, b, FP_WIDTH);
		bn_rec_naf(naf1, &l1, d, FP_WIDTH);

		l = RLC_MAX(l0, l1);
		if (bn_sign(b) == RLC_NEG) {
			for (size_t i = 0; i < l0; i++) {
				naf0[i] = -naf0[i];
			}
		}
		if (bn_sign(d) == RLC_NEG) {
			for (size_t i = 0; i < l1; i++) {
				naf1[i] = -naf1[i];
			}
		}

		_k = naf0 + l - 1;
		_m = naf1 + l - 1;

		fp2_set_dig(r, 1);
		for (int i = l - 1; i >= 0; i--, _k--, _m--) {
			fp2_sqr(r, r);

			n0 = *_k;
			n1 = *_m;

			if (n0 > 0) {
				fp2_mul(r, r, t0[n0 / 2]);
			}
			if (n0 < 0) {
				fp2_inv_cyc(s, t0[-n0 / 2]);
				fp2_mul(r, r, s);
			}
			if (n1 > 0) {
				fp2_mul(r, r, t1[n1 / 2]);
			}
			if (n1 < 0) {
				fp2_inv_cyc(s, t1[-n1 / 2]);
				fp2_mul(r, r, s);
			}
		}

		fp2_copy(e, r);
	}
	RLC_CATCH_ANY {
		RLC_THROW(ERR_CAUGHT);
	}
	RLC_FINALLY {
		fp2_free(r);
		fp2_free(s);
		for (int i = 0; i < (1 << (FP_WIDTH - 2)); i++) {
			fp2_free(t0[i]);
			fp2_free(t1[i]);
		}
	}
}