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use rustc_middle::mir;
use rustc_span::Symbol;
use rustc_target::spec::abi::Abi;

use super::{horizontal_bin_op, int_abs, pmulhrsw, psign};
use crate::*;

impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
    fn emulate_x86_ssse3_intrinsic(
        &mut self,
        link_name: Symbol,
        abi: Abi,
        args: &[OpTy<'tcx>],
        dest: &MPlaceTy<'tcx>,
    ) -> InterpResult<'tcx, EmulateItemResult> {
        let this = self.eval_context_mut();
        this.expect_target_feature_for_intrinsic(link_name, "ssse3")?;
        // Prefix should have already been checked.
        let unprefixed_name = link_name.as_str().strip_prefix("llvm.x86.ssse3.").unwrap();

        match unprefixed_name {
            // Used to implement the _mm_abs_epi{8,16,32} functions.
            // Calculates the absolute value of packed 8/16/32-bit integers.
            "pabs.b.128" | "pabs.w.128" | "pabs.d.128" => {
                let [op] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                int_abs(this, op, dest)?;
            }
            // Used to implement the _mm_shuffle_epi8 intrinsic.
            // Shuffles bytes from `left` using `right` as pattern.
            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_shuffle_epi8
            "pshuf.b.128" => {
                let [left, right] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                let (left, left_len) = this.operand_to_simd(left)?;
                let (right, right_len) = this.operand_to_simd(right)?;
                let (dest, dest_len) = this.mplace_to_simd(dest)?;

                assert_eq!(dest_len, left_len);
                assert_eq!(dest_len, right_len);

                for i in 0..dest_len {
                    let right = this.read_scalar(&this.project_index(&right, i)?)?.to_u8()?;
                    let dest = this.project_index(&dest, i)?;

                    let res = if right & 0x80 == 0 {
                        let j = right % 16; // index wraps around
                        this.read_scalar(&this.project_index(&left, j.into())?)?
                    } else {
                        // If the highest bit in `right` is 1, write zero.
                        Scalar::from_u8(0)
                    };

                    this.write_scalar(res, &dest)?;
                }
            }
            // Used to implement the _mm_h{add,adds,sub}_epi{16,32} functions.
            // Horizontally add / add with saturation / subtract adjacent 16/32-bit
            // integer values in `left` and `right`.
            "phadd.w.128" | "phadd.sw.128" | "phadd.d.128" | "phsub.w.128" | "phsub.sw.128"
            | "phsub.d.128" => {
                let [left, right] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                let (which, saturating) = match unprefixed_name {
                    "phadd.w.128" | "phadd.d.128" => (mir::BinOp::Add, false),
                    "phadd.sw.128" => (mir::BinOp::Add, true),
                    "phsub.w.128" | "phsub.d.128" => (mir::BinOp::Sub, false),
                    "phsub.sw.128" => (mir::BinOp::Sub, true),
                    _ => unreachable!(),
                };

                horizontal_bin_op(this, which, saturating, left, right, dest)?;
            }
            // Used to implement the _mm_maddubs_epi16 function.
            // Multiplies packed 8-bit unsigned integers from `left` and packed
            // signed 8-bit integers from `right` into 16-bit signed integers. Then,
            // the saturating sum of the products with indices `2*i` and `2*i+1`
            // produces the output at index `i`.
            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_maddubs_epi16
            "pmadd.ub.sw.128" => {
                let [left, right] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                let (left, left_len) = this.operand_to_simd(left)?;
                let (right, right_len) = this.operand_to_simd(right)?;
                let (dest, dest_len) = this.mplace_to_simd(dest)?;

                assert_eq!(left_len, right_len);
                assert_eq!(dest_len.strict_mul(2), left_len);

                for i in 0..dest_len {
                    let j1 = i.strict_mul(2);
                    let left1 = this.read_scalar(&this.project_index(&left, j1)?)?.to_u8()?;
                    let right1 = this.read_scalar(&this.project_index(&right, j1)?)?.to_i8()?;

                    let j2 = j1.strict_add(1);
                    let left2 = this.read_scalar(&this.project_index(&left, j2)?)?.to_u8()?;
                    let right2 = this.read_scalar(&this.project_index(&right, j2)?)?.to_i8()?;

                    let dest = this.project_index(&dest, i)?;

                    // Multiplication of a u8 and an i8 into an i16 cannot overflow.
                    let mul1 = i16::from(left1).strict_mul(right1.into());
                    let mul2 = i16::from(left2).strict_mul(right2.into());
                    let res = mul1.saturating_add(mul2);

                    this.write_scalar(Scalar::from_i16(res), &dest)?;
                }
            }
            // Used to implement the _mm_mulhrs_epi16 function.
            // Multiplies packed 16-bit signed integer values, truncates the 32-bit
            // product to the 18 most significant bits by right-shifting, and then
            // divides the 18-bit value by 2 (rounding to nearest) by first adding
            // 1 and then taking the bits `1..=16`.
            // https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#text=_mm_mulhrs_epi16
            "pmul.hr.sw.128" => {
                let [left, right] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                pmulhrsw(this, left, right, dest)?;
            }
            // Used to implement the _mm_sign_epi{8,16,32} functions.
            // Negates elements from `left` when the corresponding element in
            // `right` is negative. If an element from `right` is zero, zero
            // is writen to the corresponding output element.
            // Basically, we multiply `left` with `right.signum()`.
            "psign.b.128" | "psign.w.128" | "psign.d.128" => {
                let [left, right] =
                    this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

                psign(this, left, right, dest)?;
            }
            _ => return Ok(EmulateItemResult::NotSupported),
        }
        Ok(EmulateItemResult::NeedsReturn)
    }
}