Add the ed25519 ref10 code verbatim from supercop-20140622

We might use libsodium or ed25519-donna later on, but for now, let's
see whether this is fast enough.  We should use it in all cases when
performance doesn't matter.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/ext/ed25519/ref10/fe_isnonzero.c b/src/ext/ed25519/ref10/fe_isnonzero.c
new file mode 100644
index 0000000000..47568001ce
--- /dev/null
+++ b/src/ext/ed25519/ref10/fe_isnonzero.c
@@ -0,0 +1,19 @@
+#include "fe.h"
+#include "crypto_verify_32.h"
+
+/*
+return 1 if f == 0
+return 0 if f != 0
+
+Preconditions:
+   |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
+*/
+
+static const unsigned char zero[32];
+
+int fe_isnonzero(const fe f)
+{
+  unsigned char s[32];
+  fe_tobytes(s,f);
+  return crypto_verify_32(s,zero);
+}