Function core::intrinsics::simd::simd_bitmask
source · pub unsafe extern "rust-intrinsic" fn simd_bitmask<T, U>(x: T) -> U
core_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
0b1101u8
or[0b1101]
on little endian, and0b1011u8
or[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
0b0100001100000001u16
or[0b00000001, 0b01000011]
on little endian, and0b1000000011000010u16
or[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
0b0101001011u16
or[0b01001011, 0b01]
on little endian, and0b1101001010u16
or[0b11, 0b01001010]
on big endian.
§Safety
x
must contain only 0
and !0
.