diff options
| -rw-r--r-- | library/core/src/intrinsics/simd.rs | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/library/core/src/intrinsics/simd.rs b/library/core/src/intrinsics/simd.rs index e8a914ffee2..fcc4d014e66 100644 --- a/library/core/src/intrinsics/simd.rs +++ b/library/core/src/intrinsics/simd.rs @@ -83,7 +83,14 @@ extern "platform-intrinsic" { /// Otherwise, truncates or extends the value, maintaining the sign for signed integers. /// /// # Safety - /// Casting floats to integers truncates, but the truncated value must fit in the target type. + /// Casting from integer types is always safe. + /// Casting between two float types is also always safe. + /// + /// Casting floats to integers truncates, following the same rules as `to_int_unchecked`. + /// Specifically, each element must: + /// * Not be `NaN` + /// * Not be infinite + /// * Be representable in the return type, after truncating off its fractional part pub fn simd_cast<T, U>(x: T) -> U; /// Numerically cast a vector, elementwise. @@ -91,7 +98,7 @@ extern "platform-intrinsic" { /// `T` and `U` be a vectors of integer or floating point primitive types, and must have the /// same length. /// - /// Like `simd_cast`, but saturates float-to-integer conversions. + /// Like `simd_cast`, but saturates float-to-integer conversions (NaN becomes 0). /// This matches regular `as` and is always safe. /// /// When casting floats to integers, the result is truncated. @@ -337,6 +344,10 @@ extern "platform-intrinsic" { /// For example, `[!0, 0, !0, !0]` packs to `0b1101` on little endian and `0b1011` on big /// endian. /// + /// To consider a larger example, `[!0, 0, 0, 0, 0, 0, 0, 0, !0, !0, 0, 0, 0, 0, !0, 0]` packs + /// to `[0b00000001, 0b01000011]` or `0b0100001100000001` on little endian, and `[0b10000000, + /// 0b11000010]` or `0b1000000011000010` on big endian. + /// /// # Safety /// `x` must contain only `0` and `!0`. pub fn simd_bitmask<T, U>(x: T) -> U; |