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authorMoxie Marlinspike <moxie@thoughtcrime.org>2014-11-24 12:54:30 -0800
committerMoxie Marlinspike <moxie@thoughtcrime.org>2014-11-24 12:54:30 -0800
commit60800e155612bea797eed93c67046a23d26054cc (patch)
treed88368c1c26162e27e790195133ca2b526597afe /jni/ed25519/fe_isnegative.c
Break out into separate repo.
Diffstat (limited to 'jni/ed25519/fe_isnegative.c')
-rw-r--r--jni/ed25519/fe_isnegative.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/jni/ed25519/fe_isnegative.c b/jni/ed25519/fe_isnegative.c
new file mode 100644
index 00000000..3b2c8b8d
--- /dev/null
+++ b/jni/ed25519/fe_isnegative.c
@@ -0,0 +1,16 @@
+#include "fe.h"
+
+/*
+return 1 if f is in {1,3,5,...,q-2}
+return 0 if f is in {0,2,4,...,q-1}
+
+Preconditions:
+ |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
+*/
+
+int fe_isnegative(const fe f)
+{
+ unsigned char s[32];
+ fe_tobytes(s,f);
+ return s[0] & 1;
+}