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Diffstat (limited to 'library/core/src/intrinsics/mod.rs')
| -rw-r--r-- | library/core/src/intrinsics/mod.rs | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/library/core/src/intrinsics/mod.rs b/library/core/src/intrinsics/mod.rs index 42b8eb33a1a..1ee3b83ed22 100644 --- a/library/core/src/intrinsics/mod.rs +++ b/library/core/src/intrinsics/mod.rs @@ -68,6 +68,7 @@ use crate::marker::{DiscriminantKind, Tuple}; use crate::mem::SizedTypeProperties; use crate::{ptr, ub_checks}; +pub mod fallback; pub mod mir; pub mod simd; @@ -3305,6 +3306,34 @@ pub const fn mul_with_overflow<T: Copy>(_x: T, _y: T) -> (T, bool) { unimplemented!() } +/// Performs full-width multiplication and addition with a carry: +/// `multiplier * multiplicand + addend + carry`. +/// +/// This is possible without any overflow. For `uN`: +/// MAX * MAX + MAX + MAX +/// => (2ⁿ-1) × (2ⁿ-1) + (2ⁿ-1) + (2ⁿ-1) +/// => (2²ⁿ - 2ⁿ⁺¹ + 1) + (2ⁿ⁺¹ - 2) +/// => 2²ⁿ - 1 +/// +/// For `iN`, the upper bound is MIN * MIN + MAX + MAX => 2²ⁿ⁻² + 2ⁿ - 2, +/// and the lower bound is MAX * MIN + MIN + MIN => -2²ⁿ⁻² - 2ⁿ + 2ⁿ⁺¹. +/// +/// This currently supports unsigned integers *only*, no signed ones. +/// The stabilized versions of this intrinsic are available on integers. +#[unstable(feature = "core_intrinsics", issue = "none")] +#[rustc_const_unstable(feature = "const_carrying_mul_add", issue = "85532")] +#[rustc_nounwind] +#[cfg_attr(not(bootstrap), rustc_intrinsic)] +#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_is_spec)] +pub const fn carrying_mul_add<T: ~const fallback::CarryingMulAdd<Unsigned = U>, U>( + multiplier: T, + multiplicand: T, + addend: T, + carry: T, +) -> (U, T) { + multiplier.carrying_mul_add(multiplicand, addend, carry) +} + /// Performs an exact division, resulting in undefined behavior where /// `x % y != 0` or `y == 0` or `x == T::MIN && y == -1` /// |