fp8_to_fp16.h

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 #pragma once

#include <cutlass/half.h> 
#include <cute/util/sycl_vec.hpp>

using half_t = cutlass::half_t;
using uchar16 = cute::intel::uchar16;
using ushort16 = cute::intel::ushort16;

static inline ushort16 convert_ushort16(uchar16 x) {
    ushort16 result;
    #pragma unroll
    for (int i = 0; i < 16; ++i) {
        result[i] = static_cast<uint16_t>(x[i]);
    }
    return result;
}

static inline ushort16 E4M3_to_FP16_vec16(uchar16 xin) {
    uchar16 xa = xin & 0x7F;
    uchar16 sgn_x = xin ^ xa;

    uchar16 zero_mask;
    #pragma unroll
    for (int i = 0; i < 16; ++i) {
        zero_mask[i] = (xa[i] == 0) ? 1 : 0;
    }
    uchar16 nan_mask = (0x7E - xa) & 0x80;
    uchar16 den_mask = ((xa - 8) >> 7) & 0x01;

    xa += (nan_mask >> 1);
    xa |= (den_mask & 8);
    den_mask &= 0x48;
    xa += 0x40 & ~(zero_mask * 0x40);

    ushort16 x16 = convert_ushort16(xa) << 7;
    ushort16 den_corr = convert_ushort16(den_mask & ~zero_mask) << 7;

    ushort16 result = x16 - den_corr;
    result &= ~(convert_ushort16(zero_mask) << 7);

    ushort16 sign_ext = convert_ushort16(sgn_x) << 8;
    result ^= sign_ext;

    return result;
}

static inline unsigned short E4M3_to_FP16(unsigned char xin) {
    unsigned char xa, sgn_x, nan_mask, den_mask;

    union {
        signed short i;
        _Float16 f;
    } x16, den_corr;

    xa = xin & 0x7f;
    sgn_x = xin ^ xa;

    // mask for NaN input
    nan_mask = (0x7e - xa) & 0x80;
    // mask for denormal / zero input
    den_mask = (((signed char)(xa - 8)) >> 7);

    // apply Nan correction
    xa += (nan_mask >> 1);
    // first denormal correction
    xa |= (den_mask & 8);
    den_mask &= 0x48;
    // exponent bias correction
    xa += 0x40;

    // zero-extend to 16 bits
    x16.i = xa;
    den_corr.i = den_mask;
    // FP16 format
    x16.i <<= 7;
    den_corr.i <<= 7;

    // apply correction for denormals/zero
    x16.f -= den_corr.f;

    // finally, apply the sign
    x16.i ^= (((signed short)sgn_x) << 8);

    return (unsigned short)x16.i;
}