pub unsafe extern "rust-intrinsic" fn simd_bitmask<T, U>(x: T) -> Ucore_intrinsics)Expand description
Truncates an integer vector to a bitmask.
T must be an integer vector.
U must be either the smallest unsigned integer with at least as many bits as the length
of T, or the smallest array of u8 with at least as many bits as the length of T.
Each element is truncated to a single bit and packed into the result.
No matter whether the output is an array or an unsigned integer, it is treated as a single contiguous list of bits. The bitmask is always packed on the least-significant side of the output, and padded with 0s in the most-significant bits. The order of the bits depends on endianness:
- On little endian, the least significant bit corresponds to the first vector element.
- On big endian, the least significant bit corresponds to the last vector element.
For example, [!0, 0, !0, !0] packs to
- 0b1101u8or- [0b1101]on little endian, and
- 0b1011u8or- [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
- 0b0100001100000001u16or- [0b00000001, 0b01000011]on little endian, and
- 0b1000000011000010u16or- [0b10000000, 0b11000010]on big endian.
And finally, a non-power-of-2 example with multiple bytes:
[!0, !0, 0, !0, 0, 0, !0, 0, !0, 0] packs to
- 0b0101001011u16or- [0b01001011, 0b01]on little endian, and
- 0b1101001010u16or- [0b11, 0b01001010]on big endian.
§Safety
x must contain only 0 and !0.