File: fe_isnonzero.c

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python-axolotl-curve25519 0.4.1.post2-2
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#include "fe.h"
#include "crypto_verify_32.h"

/*
return nonzero 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.
*/

/* TREVOR'S COMMENT 
 *
 * I think the above comment is wrong.  Instead:
 *
 * return 0 if f == 0
 * return -1 if f != 0 
 *
 * */

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);
}