_mm_shuffle_epi8 in core::arch::x86 - Rust
Description: Shuffles bytes from `a` according to the content of `b`.

core::arch::x86

# Function _mm_shuffle_epi8

1.27.0 · source

    pub unsafe fn _mm_shuffle_epi8(a: __m128i, b: __m128i) -> __m128i

Available on (x86 or x86-64) and target feature `ssse3` and x86 only.
Expand description

Shuffles bytes from `a` according to the content of `b`.

The last 4 bits of each byte of `b` are used as addresses into the 16 bytes of `a`.

In addition, if the highest significant bit of a byte of `b` is set, the respective destination byte is set to 0.

Picturing `a` and `b` as `[u8; 16]`, `_mm_shuffle_epi8` is logically equivalent to:

    fn mm_shuffle_epi8(a: [u8; 16], b: [u8; 16]) -> [u8; 16] {
        let mut r = [0u8; 16];
        for i in 0..16 {
            // if the most significant bit of b is set,
            // then the destination byte is set to 0.
            if b[i] & 0x80 == 0u8 {
                r[i] = a[(b[i] % 16) as usize];
            }
        }
        r
    }

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