text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Phtevencoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "eccryptoverify.h"
  
  namespace {
  
  int CompareBigEndian(const unsigned char *c1, size_t c1len, const unsigned char *c2, size_t c2len) {
      while (c1len > c2len) {
          if (*c1)
              return 1;
          c1++;
          c1len--;
      }
      while (c2len > c1len) {
          if (*c2)
              return -1;
          c2++;
          c2len--;
      }
      while (c1len > 0) {
          if (*c1 > *c2)
              return 1;
          if (*c2 > *c1)
              return -1;
          c1++;
          c2++;
          c1len--;
      }
      return 0;
  }
  
  /** Order of secp256k1's generator minus 1. */
  const unsigned char vchMaxModOrder[32] = {
      0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
      0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFE,
      0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,
      0xBF,0xD2,0x5E,0x8C,0xD0,0x36,0x41,0x40
  };
  
  /** Half of the order of secp256k1's generator minus 1. */
  const unsigned char vchMaxModHalfOrder[32] = {
      0x7F,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
      0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
      0x5D,0x57,0x6E,0x73,0x57,0xA4,0x50,0x1D,
      0xDF,0xE9,0x2F,0x46,0x68,0x1B,0x20,0xA0
  };
  
  const unsigned char vchZero[1] = {0};
  } // anon namespace
  
  namespace eccrypto {
  
  bool Check(const unsigned char *vch) {
      return vch &&
             CompareBigEndian(vch, 32, vchZero, 0) > 0 &&
             CompareBigEndian(vch, 32, vchMaxModOrder, 32) <= 0;
  }
  
  bool CheckSignatureElement(const unsigned char *vch, int len, bool half) {
      return vch &&
             CompareBigEndian(vch, len, vchZero, 0) > 0 &&
             CompareBigEndian(vch, len, half ? vchMaxModHalfOrder : vchMaxModOrder, 32) <= 0;
  }
  
  } // namespace eccrypto
  