Restructure x86 signed pack instructions

This reduces the amount of duplicated code and the chance for bugs.

I validated the new code for correctness against LLVM using the
following script. It found many bugs in the implementation until I was
finally able to get it correct and passing.

```rust
//! Test for x86 pack instructions. Prints deterministic results, use it to compare backends.
use std::arch::x86_64::{self, __m128i, __m256i};
use rand::{rngs::SmallRng, Rng, SeedableRng};
fn main() {
    let rng = &mut SmallRng::seed_from_u64(123);
    for _ in 0..100_000 {
        unsafe {
            sse_test(rng);
            avx_test(rng);
        }
    }
}
unsafe fn sse_test(rng: &mut SmallRng) {
    print_sse_8(x86_64::_mm_packus_epi16(sse16(rng), sse16(rng)));
    print_sse_8(x86_64::_mm_packs_epi16(sse16(rng), sse16(rng)));
    print_sse_16(x86_64::_mm_packus_epi32(sse32(rng), sse32(rng)));
    print_sse_16(x86_64::_mm_packs_epi32(sse32(rng), sse32(rng)));
}
unsafe fn avx_test(rng: &mut SmallRng) {
    print_avx_8(x86_64::_mm256_packs_epi16(avx16(rng), avx16(rng)));
    print_avx_8(x86_64::_mm256_packs_epi16(avx16(rng), avx16(rng)));
    print_avx_16(x86_64::_mm256_packus_epi32(avx32(rng), avx32(rng)));
    print_avx_16(x86_64::_mm256_packs_epi32(avx32(rng), avx32(rng)));
}
fn print_sse_8(t: __m128i) {
    let ints = unsafe { std::mem::transmute::<_, [i8; 16]>(t) };
    println!("{ints:?}");
}
fn print_sse_16(t: __m128i) {
    let ints = unsafe { std::mem::transmute::<_, [i16; 8]>(t) };
    println!("{ints:?}");
}
fn print_avx_8(t: __m256i) {
    let ints = unsafe { std::mem::transmute::<_, [i8; 32]>(t) };
    println!("{ints:?}");
}
fn print_avx_16(t: __m256i) {
    let ints = unsafe { std::mem::transmute::<_, [i16; 16]>(t) };
    println!("{ints:?}");
}
fn sse16(rand: &mut SmallRng) -> __m128i {
    unsafe { std::mem::transmute([(); 8].map(|()| i16(rand))) }
}
fn sse32(rand: &mut SmallRng) -> __m128i {
    unsafe { std::mem::transmute([(); 4].map(|()| i32(rand))) }
}
fn avx16(rand: &mut SmallRng) -> __m256i {
    unsafe { std::mem::transmute([(); 16].map(|()| i16(rand))) }
}
fn avx32(rand: &mut SmallRng) -> __m256i {
    unsafe { std::mem::transmute([(); 8].map(|()| i32(rand))) }
}
fn i16(rand: &mut SmallRng) -> i16 {
    if rand.gen() {
        rand.gen::<i16>()
    } else {
        rand.gen::<i8>() as i16
    }
}
fn i32(rand: &mut SmallRng) -> i32 {
    if rand.gen() {
        rand.gen::<i32>()
    } else {
        rand.gen::<i16>() as i32
    }
}
```

0 files changed, 0 insertions, 0 deletions