X-Git-Url: https://git.distorted.org.uk/u/mdw/putty/blobdiff_plain/9c6214334f866ab91173df992180e168c17f904d..7d6ee6ff291302d003f6f6cc6d11cede050c1c87:/sshbn.c

diff --git a/sshbn.c b/sshbn.c
index 693b4ac7..24af76fb 100644
--- a/sshbn.c
+++ b/sshbn.c
@@ -11,6 +11,20 @@
 unsigned short bnZero[1] = { 0 };
 unsigned short bnOne[2] = { 1, 1 };
 
+/*
+ * The Bignum format is an array of `unsigned short'. The first
+ * element of the array counts the remaining elements. The
+ * remaining elements express the actual number, base 2^16, _least_
+ * significant digit first. (So it's trivial to extract the bit
+ * with value 2^n for any n.)
+ *
+ * All Bignums in this module are positive. Negative numbers must
+ * be dealt with outside it.
+ *
+ * INVARIANT: the most significant word of any Bignum must be
+ * nonzero.
+ */
+
 Bignum Zero = bnZero, One = bnOne;
 
 Bignum newbn(int length) {