Clarify preconditions and impact if not met
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index b8e0807..cd78e72 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -824,14 +824,16 @@
/** Compute GCD(A, N) and optionally the inverse of A mod N if it exists.
*
- * Requires N to be odd, and 0 <= A <= N.
- * When I != NULL, N (the modulus) must not be 1.
+ * Requires N to be odd, 0 <= A <= N and A_limbs <= N_limbs.
+ * When I != NULL, N (the modulus) must be greater than 1.
*
* A and N may not alias each other.
* When I == NULL (computing only the GCD), G may alias A or N.
* When I != NULL (computing the modular inverse), G or I may alias A
* but none of them may alias N (the modulus).
*
+ * If any precondition is not met, output values are unspecified.
+ *
* \param[out] G The GCD of \p A and \p N.
* Must have the same number of limbs as \p N.
* \param[out] I The inverse of \p A modulo \p N if it exists (that is,
@@ -843,7 +845,8 @@
* \param A_limbs The number of limbs of \p A.
* Must be less than or equal to \p N_limbs.
* \param[in] N The 2nd operand of GCD and modulus for inversion.
- * Must be odd or the results are indeterminate.
+ * This value must be odd.
+ * If I != NULL this value must be greater than 1.
* \param N_limbs The number of limbs of \p N.
* \param[in,out] T Temporary storage of size at least 5 * N_limbs limbs,
* or 4 * N_limbs if \p I is NULL (GCD only).