BN_sub: document that r might be the same as a or b

Reviewed-by: Rich Salz <rsalz@akamai.com>
RT #4100, MR #1264

diff --git a/doc/crypto/BN_add.pod b/doc/crypto/BN_add.pod
index 942048c10d0b30211106b95222e30697862afb4f..3ad227458da89a5dae7d1d84bbe38be92297909f 100644 (file)
--- a/doc/crypto/BN_add.pod
+++ b/doc/crypto/BN_add.pod
@@ -49,6 +49,7 @@ BN_add() adds I<a> and I<b> and places the result in I<r> (C<r=a+b>).
 I<r> may be the same B<BIGNUM> as I<a> or I<b>.
 
 BN_sub() subtracts I<b> from I<a> and places the result in I<r> (C<r=a-b>).
+I<r> may be the same B<BIGNUM> as I<a> or I<b>.
 
 BN_mul() multiplies I<a> and I<b> and places the result in I<r> (C<r=a*b>).
 I<r> may be the same B<BIGNUM> as I<a> or I<b>.