How to use RDRAND intrinsics?

问题

I was looking at H.J. Lu's PATCH: Update x86 rdrand intrinsics. I can't tell if I should be using _rdrand_u64, _rdrand64_step, or if there are other function(s). There does not appear to be test cases written for them.

There also seems to be a lack of man pages (from Ubuntu 14, GCC 4.8.4):

$ man -k rdrand
rdrand: nothing appropriate.

How does one use the RDRAND intrinsics to generate, say, a block of 32 bytes?

A related question is RDRAND and RDSEED intrinsics GCC and Intel C++. But it does not tell me how to use them, or how to generate a block.

回答1:

If you look at <immintrin.h> (mine is in `/usr/lib/gcc/x86_64-linux-gnu/4.9/include/', Ubuntu 15.04 64bit), there are compatible (with MSVC, Intel CC) functions defined which pass data back to GCC built-ins

extern __inline int __attribute__((__gnu_inline__, __always_inline__, __artificial__))
_rdrand64_step (unsigned long long *__P)
{
     return __builtin_ia32_rdrand64_step (__P);
}

for 64bit parameter and two others for 16 bit and 32bit parameters

_rdrand16_step (unsigned short *__P)
_rdrand32_step (unsigned int *__P)

You supposed to use those so your code would be compatible with MSVC, Intel CC and other compilers.

_rdrand64_step will fill 64bit parameter, passed by pointer, with random bits and return error code. Ditto for 32bit and 16bit versions

UPDATE

"These intrinsics generate random numbers of 16/32/64 bit wide random integers. The generated random value is written to the given memory location and the success status is returned: '1' if the hardware returned a valid random value, and '0' otherwise."

https://software.intel.com/en-us/node/523864

来源：https://stackoverflow.com/questions/31214457/how-to-use-rdrand-intrinsics

标签

gcc

intrinsics

rdrand