src/fuzzer/gcd.cpp


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/*
* (C) 2021 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include "fuzzers.h"
#include <botan/numthry.h>

namespace {

Botan::BigInt ref_gcd(Botan::BigInt a,
                      Botan::BigInt b)
   {
   Botan::BigInt t;
   while(b != 0)
      {
      t = a % b;
      t.swap(b);
      t.swap(a);
      }
   return a;
   }

}

void fuzz(const uint8_t in[], size_t len)
   {
   static const size_t max_bits = 4096;

   if(2*len*8 > max_bits)
      return;

   const Botan::BigInt x = Botan::BigInt::decode(in, len / 2);
   const Botan::BigInt y = Botan::BigInt::decode(in + len / 2, len - (len / 2));

   const Botan::BigInt ref = ref_gcd(x, y);
   const Botan::BigInt lib = Botan::gcd(x, y);

   if(ref != lib)
      {
      FUZZER_WRITE_AND_CRASH("X = " << x << "\n"
                             << "Y = " << y << "\n"
                             << "L = " << lib << "\n"
                             << "R = " << ref << "\n");
      }
   }