bignum_mod_raw: Added modular negation.
This patch adds the `mpi_mod_raw_neg()` method.
Co-authored-by: Hanno Becker <hanno.becker@arm.com>
Co-authored-by: Minos Galanakis <minos.galanakis@arm.com>
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/library/bignum_mod_raw.c b/library/bignum_mod_raw.c
index 22e56b7..138d5a0 100644
--- a/library/bignum_mod_raw.c
+++ b/library/bignum_mod_raw.c
@@ -182,6 +182,18 @@
mbedtls_free( T );
return( 0 );
}
+
+void mbedtls_mpi_mod_raw_neg( mbedtls_mpi_uint *X,
+ const mbedtls_mpi_uint *A,
+ const mbedtls_mpi_mod_modulus *m )
+{
+ mbedtls_mpi_core_sub( X, m->p, A, m->limbs );
+
+ /* If A=0 initially, then X=N now. Detect this by
+ * subtracting N and catching the carry. */
+ mbedtls_mpi_uint borrow = mbedtls_mpi_core_sub( X, X, m->p, m->limbs );
+ (void) mbedtls_mpi_core_add_if( X, m->p, m->limbs, (unsigned) borrow );
+}
/* END MERGE SLOT 7 */
/* BEGIN MERGE SLOT 8 */