release/src/router/libsodium/src/libsodium/crypto_sign/ed25519/ref10/fe_isnegative.c

   1 #include "fe.h"
   2
   3 /*
   4 return 1 if f is in {1,3,5,...,q-2}
   5 return 0 if f is in {0,2,4,...,q-1}
   6
   7 Preconditions:
   8    |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
   9 */
  10
  11 int fe_isnegative(const fe f)
  12 {
  13   unsigned char s[32];
  14   fe_tobytes(s,f);
  15   return s[0] & 1;
  16 }