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Fix unsoundness in new is_power_of_two fast path #120546

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Fix unsoundness in new is_power_of_two fast path #120546

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16 changes: 8 additions & 8 deletions library/core/src/num/int_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1389,9 +1389,9 @@ macro_rules! int_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self.wrapping_abs()) as u32 };
if exp > Self::BITS / power_used { return None; } // Division of constants is free
if exp >= Self::BITS / power_used { return None; } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
let res = unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -2106,9 +2106,9 @@ macro_rules! int_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self.wrapping_abs()) as u32 };
if exp > Self::BITS / power_used { return 0; } // Division of constants is free
if exp >= Self::BITS / power_used { return 0; } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
let res = unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -2640,9 +2640,9 @@ macro_rules! int_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self.wrapping_abs()) as u32 };
if exp > Self::BITS / power_used { return (0, true); } // Division of constants is free
if exp >= Self::BITS / power_used { return (0, true); } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
let res = unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -2721,12 +2721,12 @@ macro_rules! int_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self.wrapping_abs()) as u32 };
if exp > Self::BITS / power_used { // Division of constants is free
if exp >= Self::BITS / power_used { // Division of constants is free
#[allow(arithmetic_overflow)]
return Self::MAX * Self::MAX * 0;
}

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
let res = unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down
16 changes: 8 additions & 8 deletions library/core/src/num/uint_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1376,9 +1376,9 @@ macro_rules! uint_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self) as u32 };
if exp > Self::BITS / power_used { return None; } // Division of constants is free
if exp >= Self::BITS / power_used { return None; } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
unsafe { Some(intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -1920,9 +1920,9 @@ macro_rules! uint_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self) as u32 };
if exp > Self::BITS / power_used { return 0; } // Division of constants is free
if exp >= Self::BITS / power_used { return 0; } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -2395,9 +2395,9 @@ macro_rules! uint_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self) as u32 };
if exp > Self::BITS / power_used { return (0, true); } // Division of constants is free
if exp >= Self::BITS / power_used { return (0, true); } // Division of constants is free

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
unsafe { (intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down Expand Up @@ -2475,12 +2475,12 @@ macro_rules! uint_impl {
}
// SAFETY: We just checked this is a power of two. and above zero.
let power_used = unsafe { intrinsics::cttz_nonzero(self) as u32 };
if exp > Self::BITS / power_used { // Division of constants is free
if exp >= Self::BITS / power_used { // Division of constants is free
#[allow(arithmetic_overflow)]
return Self::MAX * Self::MAX * 0;
}

// SAFETY: exp <= Self::BITS / power_used
// SAFETY: exp < Self::BITS / power_used
unsafe { intrinsics::unchecked_shl(
1 as Self,
intrinsics::unchecked_mul(power_used, exp) as Self
Expand Down
1 change: 1 addition & 0 deletions library/core/tests/num/int_macros.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -288,6 +288,7 @@ macro_rules! int_module {
assert_eq!(r.saturating_pow(2), 4 as $T);
assert_eq!(r.saturating_pow(3), -8 as $T);
assert_eq!(r.saturating_pow(0), 1 as $T);
assert_eq!(2i64.checked_pow(64), None); // issue #120537
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These tests are expanded for all integer types $T, so it would be nice to keep it testing each type. In this signed case, above where r = 2 as $T we can check exponent <$T>::BITS - 1 produces None, and with r = -2 we can check that BITS - 1 is Some(<$T>::MIN) and BITS gets None.

}

#[test]
Expand Down
1 change: 1 addition & 0 deletions library/core/tests/num/uint_macros.rs
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Expand Up @@ -204,6 +204,7 @@ macro_rules! uint_module {
assert_eq!(r.checked_pow(2), None);
assert_eq!(r.overflowing_pow(2), (1 as $T, true));
assert_eq!(r.saturating_pow(2), MAX);
assert_eq!(2u64.checked_pow(64), None); // issue #120537
}

#[test]
Expand Down