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rdrand: Avoid inlining unrolled retry loops. #444

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+20 −10
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rdrand: Avoid inlining unrolled retry loops. #444

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30 changes: 20 additions & 10 deletions src/rdrand.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,20 +14,30 @@ cfg_if! {
}
}

// 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.
const RETRY_LIMIT: usize = 10;

#[target_feature(enable = "rdrand")]
unsafe fn rdrand() -> Option<Word> {
for _ in 0..RETRY_LIMIT {
let mut val = 0;
if rdrand_step(&mut val) == 1 {
return Some(val);
#[cold]
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()
}
None
}

// "rdrand" target feature requires "+rdrand" flag, see https://github.com/rust-lang/rust/issues/49653.
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