Explain how the code relates to the description in HAC

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-15 22:09:39 +02:00
parent ae7f75c908
commit 6537bdb5e0

View file

@ -2424,6 +2424,13 @@ int mbedtls_mpi_gcd( mbedtls_mpi *G, const mbedtls_mpi *A, const mbedtls_mpi *B
TA.s = TB.s = 1;
/* We follow the procedure described in HAC 14.54, except that sequences
* of divisions by 2 are grouped into a single shift. The procedure in HAC
* assumes that the numbers are initially positive. The case B=0 was
* short-circuited above. If A=0, the loop goes through 0 iterations
* and the result is correctly B.
*/
while( mbedtls_mpi_cmp_int( &TA, 0 ) != 0 )
{
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &TA, mbedtls_mpi_lsb( &TA ) ) );