ab_riscv_interpreter/rv32/zk/zbkx/
rv32_zbkx_helpers.rs

1//! Opaque helpers for Zbkx extension
2
3#[inline]
4#[doc(hidden)]
5#[cfg_attr(feature = "no-panic", no_panic_const::no_panic)]
6pub fn xperm4(rs1: u32, rs2: u32) -> u32 {
7    // TODO: Miri is excluded because corresponding intrinsic is not implemented there
8    cfg_select! {
9        all(not(miri), target_arch = "riscv32", target_feature = "zbkx") => {
10            unsafe { core::arch::riscv32::xperm4(rs1 as usize, rs2 as usize) as u32 }
11        }
12        _ => {
13            use core::simd::num::SimdUint;
14            use core::simd::{simd_swizzle, u32x8};
15
16            const SHIFT: u32x8 = u32x8::from_array([0, 4, 8, 12, 16, 20, 24, 28]);
17            const MASK: u32x8 = u32x8::splat(0xf);
18
19            // Unpack nibbles of rs1 into bytes via SIMD: broadcast, shift per-lane, mask
20            let lut = (u32x8::splat(rs1) >> SHIFT) & MASK;
21            // Unpack nibbles of rs2 into byte indices via SIMD
22            let idx = (u32x8::splat(rs2) >> SHIFT) & MASK;
23            // For each nibble of rs2, look up from lut (out-of-bounds -> 0 via swizzle_dyn)
24            let nibbles = lut.cast().swizzle_dyn(idx.cast());
25            // Pack nibbles back: interleave even/odd lanes and fold into bytes
26            let lo = simd_swizzle!(nibbles, [0, 2, 4, 6]);
27            let hi = simd_swizzle!(nibbles, [1, 3, 5, 7]);
28            u32::from_le_bytes((lo | (hi << 4)).to_array())
29        }
30    }
31}
32
33#[inline]
34#[doc(hidden)]
35#[cfg_attr(feature = "no-panic", no_panic_const::no_panic)]
36pub fn xperm8(rs1: u32, rs2: u32) -> u32 {
37    // TODO: Miri is excluded because corresponding intrinsic is not implemented there
38    cfg_select! {
39        all(not(miri), target_arch = "riscv32", target_feature = "zbkx") => {
40            unsafe { core::arch::riscv32::xperm8(rs1 as usize, rs2 as usize) as u32 }
41        }
42        _ => {
43            use core::simd::u8x4;
44
45            let lut = u8x4::from_array(rs1.to_le_bytes());
46            let idx = u8x4::from_array(rs2.to_le_bytes());
47
48            let result = lut.swizzle_dyn(idx);
49
50            u32::from_le_bytes(result.to_array())
51        }
52    }
53}
ab_riscv_interpreter/rv32/zk/zbkx/rv32_zbkx_helpers.rs

ab_riscv_interpreter/rv32/zk/zbkx/
rv32_zbkx_helpers.rs
