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doc: clarify xgcd_vartime delegates to constant-time xgcd (pending #853) #1333

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doc: clarify xgcd_vartime delegates to constant-time xgcd (pending #853) #1333

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a867b1b
doc: clarify xgcd_vartime delegates to CT xgcd pending #853
LuisCastellanos-dev Aug 8, 2026
48566d2
doc: remove test block, keep only comment clarification
LuisCastellanos-dev Aug 8, 2026
2717a6d
gcd: document xgcd_vartime delegation to xgcd
LuisCastellanos-dev Aug 28, 2026
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30 changes: 27 additions & 3 deletions src/uint/gcd.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -398,7 +398,15 @@ impl<const LIMBS: usize> Xgcd for Uint<LIMBS> {
}

fn xgcd_vartime(&self, rhs: &Uint<LIMBS>) -> Self::Output {
// TODO(#853): implement vartime
// TODO(#853): implement variable-time version.
//
// NOTE: this currently delegates to the constant-time `xgcd` implementation.
// Callers expecting variable-time performance should be aware that this runs
// in constant time and may be significantly slower than a true vartime algorithm.
//
// WARNING: when issue #853 is resolved, this will switch to a variable-time
// implementation. Callers that currently rely on constant-time behavior for
// security properties MUST NOT use `xgcd_vartime`.
self.xgcd(rhs)
}
}
Expand All @@ -411,7 +419,15 @@ impl<const LIMBS: usize> Xgcd for NonZeroUint<LIMBS> {
}

fn xgcd_vartime(&self, rhs: &NonZeroUint<LIMBS>) -> Self::Output {
// TODO(#853): implement vartime
// TODO(#853): implement variable-time version.
//
// NOTE: this currently delegates to the constant-time `xgcd` implementation.
// Callers expecting variable-time performance should be aware that this runs
// in constant time and may be significantly slower than a true vartime algorithm.
//
// WARNING: when issue #853 is resolved, this will switch to a variable-time
// implementation. Callers that currently rely on constant-time behavior for
// security properties MUST NOT use `xgcd_vartime`.
self.xgcd(rhs)
}
}
Expand All @@ -424,7 +440,15 @@ impl<const LIMBS: usize> Xgcd for OddUint<LIMBS> {
}

fn xgcd_vartime(&self, rhs: &OddUint<LIMBS>) -> Self::Output {
// TODO(#853): implement vartime
// TODO(#853): implement variable-time version.
//
// NOTE: this currently delegates to the constant-time `xgcd` implementation.
// Callers expecting variable-time performance should be aware that this runs
// in constant time and may be significantly slower than a true vartime algorithm.
//
// WARNING: when issue #853 is resolved, this will switch to a variable-time
// implementation. Callers that currently rely on constant-time behavior for
// security properties MUST NOT use `xgcd_vartime`.
self.xgcd(rhs)
}
}
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