Make mbedtls_mpi_gcd() more consistent
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/bignum.c b/library/bignum.c
index 7d5103e..96cade4 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1834,18 +1834,19 @@
MBEDTLS_MPI_CHK(mbedtls_mpi_copy(&TB, B));
TA.s = TB.s = 1;
- /* Handle special cases (that don't happen in crypto usage) */
- if (mbedtls_mpi_core_check_zero_ct(A.p, A.n) == MBEDTLS_CT_FALSE) {
- return mbedtls_mpi_copy(G, TB); // GCD(0, B) = abs(B)
- }
- if (mbedtls_mpi_core_check_zero_ct(B.p, B.n) == MBEDTLS_CT_FALSE) {
- return mbedtls_mpi_copy(G, A); // GCD(A, 0) = A (for now)
- }
-
- /* Make the two values the same (non-zero) number of limbs */
+ /* Make the two values the same (non-zero) number of limbs.
+ * This is needed to use mbedtls_mpi_core functions below. */
MBEDTLS_MPI_CHK(mbedtls_mpi_grow(&TA, TB.n != 0 ? TB.n : 1));
MBEDTLS_MPI_CHK(mbedtls_mpi_grow(&TB, TA.n)); // non-zero from above
+ /* Handle special cases (that don't happen in crypto usage) */
+ if (mbedtls_mpi_core_check_zero_ct(TA.p, TA.n) == MBEDTLS_CT_FALSE) {
+ return mbedtls_mpi_copy(G, &TB); // GCD(0, B) = abs(B)
+ }
+ if (mbedtls_mpi_core_check_zero_ct(TB.p, TB.n) == MBEDTLS_CT_FALSE) {
+ return mbedtls_mpi_copy(G, &TA); // GCD(A, 0) = abs(A)
+ }
+
const size_t za = mbedtls_mpi_lsb(&TA);
const size_t zb = mbedtls_mpi_lsb(&TB);