/*

* RDRAND RNG

* (C) 2016,2019 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/rdrand_rng.h>

#include <botan/loadstor.h>

#include <botan/cpuid.h>

#if !defined(BOTAN_USE_GCC_INLINE_ASM)

  #include <immintrin.h>

#endif

namespace Botan {

namespace {

#if defined(BOTAN_TARGET_ARCH_IS_X86_64)

   typedef uint64_t rdrand_output;

#else

   typedef uint32_t rdrand_output;

#endif

BOTAN_FUNC_ISA("rdrnd")

rdrand_output read_rdrand()

   {

   /*

   * According to Intel, RDRAND is guaranteed to generate a random

   * number within 10 retries on a working CPU

   */

   const size_t RDRAND_RETRIES = 10;

   for(size_t i = 0; i < RDRAND_RETRIES; ++i)

      {

      rdrand_output r = 0;

      int cf = 0;

#if defined(BOTAN_USE_GCC_INLINE_ASM)

      // same asm seq works for 32 and 64 bit

      asm("rdrand %0; adcl $0,%1" :

          "=r" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");

#elif defined(BOTAN_TARGET_ARCH_IS_X86_64)

      cf = _rdrand64_step(&r);

#else

      cf = _rdrand32_step(&r);

#endif

      if(1 == cf)

         {

         return r;

         }

      }

   throw PRNG_Unseeded("RDRAND read failed");

   }

}

void RDRAND_RNG::randomize(uint8_t out[], size_t out_len)

   {

   while(out_len >= sizeof(rdrand_output))

      {

      const rdrand_output r = read_rdrand();

      store_le(r, out);

      out += sizeof(rdrand_output);

      out_len -= sizeof(rdrand_output);

      }

   if(out_len > 0) // at most sizeof(rdrand_output)-1

      {

      const rdrand_output r = read_rdrand();

      for(size_t i = 0; i != out_len; ++i)

         out[i] = get_byte(i, r);

      }

   }

RDRAND_RNG::RDRAND_RNG()

   {

   if(!RDRAND_RNG::available())

      throw Invalid_State("Current CPU does not support RDRAND instruction");

   }

//static

bool RDRAND_RNG::available()

   {

   return CPUID::has_rdrand();

   }

//static

uint32_t RDRAND_RNG::rdrand()

   {

   return static_cast<uint32_t>(read_rdrand());

   }

//static

BOTAN_FUNC_ISA("rdrnd")

uint32_t RDRAND_RNG::rdrand_status(bool& ok)

   {

   ok = false;

   try

      {

      const uint32_t r = static_cast<uint32_t>(read_rdrand());

      ok = true;

      return r;

      }

   catch(PRNG_Unseeded&) {}

   return 0;

   }

}