1 files changed, 21 insertions, 0 deletions
diff --git a/libs/libaxolotl/src/curve25519/ed25519/additions/sc_cmov.c b/libs/libaxolotl/src/curve25519/ed25519/additions/sc_cmov.c
new file mode 100644
index 0000000000..443a5bb71e
--- /dev/null
+++ b/libs/libaxolotl/src/curve25519/ed25519/additions/sc_cmov.c
@@ -0,0 +1,21 @@
+#include "crypto_additions.h"
+
+/*
+Replace (f,g) with (g,g) if b == 1;
+replace (f,g) with (f,g) if b == 0.
+
+Preconditions: b in {0,1}.
+*/
+
+void sc_cmov(unsigned char* f, const unsigned char* g, unsigned char b)
+{
+  int count=32;
+  unsigned char x[32];
+  for (count=0; count < 32; count++)
+    x[count] = f[count] ^ g[count];
+  b = -b;
+  for (count=0; count < 32; count++)
+    x[count] &= b;
+  for (count=0; count < 32; count++)
+    f[count] = f[count] ^ x[count];
+}