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/*
* Entropy Source Using Intel's rdrand instruction
* (C) 2012,2015 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/rdrand.h>
#include <botan/cpuid.h>
#include <botan/exceptn.h>
#include <botan/build.h>
#if !defined(BOTAN_USE_GCC_INLINE_ASM)
#include <immintrin.h>
#endif
// RDRAND is guaranteed to generate a random number within 10 retries on a working CPU
#define INTEL_RDRAND_RETRIES 10
namespace Botan {
uint32_t Intel_Rdrand::get32BitRandom() {
for ( size_t i = 0; i != INTEL_RDRAND_RETRIES; ++i )
{
uint32_t r = 0;
#if defined(BOTAN_USE_GCC_INLINE_ASM)
int cf = 0;
// Encoding of rdrand %eax
asm( ".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
"=a" ( r ), "=r" ( cf ) : "0" ( r ), "1" ( cf ) : "cc" );
#else
int cf = _rdrand32_step( &r );
#endif
if ( 1 == cf )
{
return r;
}
}
throw Internal_Error( "RdRand failed after " + std::to_string( INTEL_RDRAND_RETRIES ) + " retries" );
}
void Intel_Rdrand::poll( Entropy_Accumulator& accum ) {
if ( !CPUID::has_rdrand() )
return;
for ( size_t i = 0; i != BOTAN_ENTROPY_INTEL_RNG_POLLS; ++i )
{
uint32_t random = get32BitRandom();
accum.add( random, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG );
}
}
}
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