1 files changed, 21 insertions, 18 deletions
diff --git a/src/lib/entropy/rdrand/rdrand.cpp b/src/lib/entropy/rdrand/rdrand.cpp
index 36eaebee3..ef8c5882d 100644
--- a/src/lib/entropy/rdrand/rdrand.cpp
+++ b/src/lib/entropy/rdrand/rdrand.cpp
@@ -1,26 +1,26 @@
 /*
 * Entropy Source Using Intel's rdrand instruction
 * (C) 2012,2015 Jack Lloyd
+* (C) 2015 Daniel Neus
 *
 * 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>
+#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 )
+namespace {
+
+/// @returns 0 if RdRand failed after @param max_retries otherwise the 32 bit random number generated by RdRand
+uint32_t get_32bit_random(const uint32_t max_retries) {
+   for(size_t i = 0; i != max_retries; ++i)
       {
       uint32_t r = 0;
 
@@ -28,28 +28,31 @@ uint32_t Intel_Rdrand::get32BitRandom() {
       int cf = 0;
 
       // Encoding of rdrand %eax
-      asm( ".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
-           "=a" ( r ), "=r" ( cf ) : "0" ( r ), "1" ( cf ) : "cc" );
+      asm(".byte 0x0F, 0xC7, 0xF0; adcl $0,%1" :
+      "=a" (r), "=r" (cf) : "0" (r), "1" (cf) : "cc");
 #else
-      int cf = _rdrand32_step( &r );
+      int cf = _rdrand32_step(&r);
 #endif
-      if ( 1 == cf )
+      if(1 == cf)
          {
          return r;
          }
       }
-
-   throw Internal_Error( "RdRand failed after " + std::to_string( INTEL_RDRAND_RETRIES ) + " retries" );
+   return 0;
    }
+}
 
-void Intel_Rdrand::poll( Entropy_Accumulator& accum ) {
-   if ( !CPUID::has_rdrand() )
+void Intel_Rdrand::poll(Entropy_Accumulator& accum) {
+   if(!CPUID::has_rdrand())
       return;
 
-   for ( size_t i = 0; i != BOTAN_ENTROPY_INTEL_RNG_POLLS; ++i )
+   for(size_t i = 0; i != BOTAN_ENTROPY_INTEL_RNG_POLLS; ++i)
       {
-      uint32_t random = get32BitRandom();
-      accum.add( random, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG );
+      uint32_t random = get_32bit_random(BOTAN_ENTROPY_RDRAND_RETRIES);
+      if(random)
+         {
+         accum.add(random, BOTAN_ENTROPY_ESTIMATE_HARDWARE_RNG);
+         }
       }
    }