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mrustc (master)
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//! RDRAND backend for x86(-64) targets use core::mem::{size_of, MaybeUninit}; #[inline(always)] fn slice_as_uninit<T>(slice: &[T]) -> &[MaybeUninit<T>] { let ptr = slice as *const [T] as *const [MaybeUninit<T>]; // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`. unsafe { &*ptr } } use core::arch::x86_64 as arch; use arch::_rdrand64_step as rdrand_step; type Word = u64; #[target_feature(enable = "rdrand")] unsafe fn rdrand() -> Option<Word> { #[cold] #[target_feature(enable = "rdrand")] unsafe fn retry() -> Option<Word> { // Recommendation from "Intel® Digital Random Number Generator (DRNG) Software // Implementation Guide" - Section 5.2.1 and "Intel® 64 and IA-32 Architectures // Software Developer’s Manual" - Volume 1 - Section 7.3.17.1. // Start at 1 because the caller already tried once. for _ in 1..10 { let mut val = 0; if rdrand_step(&mut val) == 1 { return Some(val); } } None } let mut val = 0; if rdrand_step(&mut val) == 1 { Some(val) } else { retry() } } // TODO: make this function safe when we have feature(target_feature_11) #[target_feature(enable = "rdrand")] pub unsafe fn rdrand_exact(dest: &mut [MaybeUninit<u8>]) -> Option<()> { // We use chunks_exact_mut instead of chunks_mut as it allows almost all // calls to memcpy to be elided by the compiler. let mut chunks = dest.chunks_exact_mut(size_of::<Word>()); for chunk in chunks.by_ref() { let src = rdrand()?.to_ne_bytes(); chunk.copy_from_slice(slice_as_uninit(&src)); } let tail = chunks.into_remainder(); let n = tail.len(); if n > 0 { let src = rdrand()?.to_ne_bytes(); tail.copy_from_slice(slice_as_uninit(&src[..n])); } Some(()) }
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