Am 24.10.2015 um 03:16 schrieb Jeffrey Walton:
>
>
> On Sunday, October 18, 2015 at 8:23:32 PM UTC-4, Jeffrey Walton wrote:
>
>
> The only thing left to do with it is
> a) verify that I actually did the opcode right [1]
>
>
> By the way, I think RDSEED detection code should look similar to
> the following. Also see the discussion of Highest Function level
> at
> https://en.wikipedia.org/wiki/CPUID#EAX.3D0:_Highest_Function_Parameter
> <https://en.wikipedia.org/wiki/CPUID#EAX.3D0:_Highest_Function_Parameter>
> ...
>
>
> Here's what the RDSEED detection code ended up being. AMD does not
> offer RDSEED, so we need to filter the call for Intel processors.
I think the run-time detection code should be in cpu.h and cpu.cpp and
not in rdrand.h and rdrand.cpp. There is already AMD / Intel and feature
detection code and our code would fit perfectly there. The outside (of
cpu.XXX) could access via HasRdRand() and HasRdSeed().
BR
JPM
>
> static bool IsIntel(const word32 output[4])
> {
> // This is the "GenuineIntel" string
> return (output[1] /*EBX*/ == 0x756e6547) &&
> (output[2] /*ECX*/ == 0x6c65746e) &&
> (output[3] /*EDX*/ == 0x49656e69);
> }
>
> static bool IsAMD(const word32 output[4])
> {
> // This is the "AuthenticAMD" string
> return (output[1] /*EBX*/ == 0x68747541) &&
> (output[2] /*ECX*/ == 0x69746E65) &&
> (output[3] /*EDX*/ == 0x444D4163);
> }
>
> static bool RDSEED_Runtime_Helper()
> {
> #if defined(CRYPTOPP_CPUID_AVAILABLE)
> bool rdseed = false; word32 output[4];
> if (CpuId(0, output))
> {
> // Only Intel supports RDSEED at the moment.
> if (IsIntel(output))
> {
> if (output[0] /*EAX*/ >= 7 && CpuId(7, output))
> {
> static const unsigned int RDSEED_FLAG = (1 << 18);
> rdseed = !!(output[1] /*EBX*/ & RDSEED_FLAG);
> }
> }
> }
> return rdseed;
> #else
> return false;
> #endif
> }
>
>
> And the updated RDRAND helper routine:
>
> static bool RDRAND_Runtime_Helper()
> {
> #if defined(CRYPTOPP_CPUID_AVAILABLE)
> bool rdrand = false; word32 output[4];
> if (CpuId(0, output))
> {
> if (IsIntel(output) || IsAMD(output))
> {
> if (output[0] /*EAX*/ >= 1 && CpuId(1, output))
> {
> static const unsigned int RDRAND_FLAG = (1 << 30);
> rdrand = !!(output[2] /*ECX*/ & RDRAND_FLAG);
> }
> }
> }
> return rdrand;
> #else
> return false;
> #endif
> }
>
> Jeff
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