ℓRGB -> sRGB Quintic Conversion (Draft!)

[[nodiscard]] inline static float _helper(float a) noexcept {
    constexpr int32_t P0=0x44c3cb8c, P1=0x10, P2=0x1554; //Magic!
    constexpr float
        s     =  0x1.0e153cp+0f , // ≈  1.055
        BIAS  = -0x1.c28efp-5f  , // ≈ -0.055
        sA    =  0x1.68f75ap-4f , // ≈  s(1/n), (note n=12)
        sB    =  0x1.863818p-5f , // ≈  s(1+n)/(2n²)
        sC    =  0x1.0e774cp-5f , // ≈  s(1+n)(1+2n)/(6n³)
        sD    =  0x1.a429e8p-6f , // ≈  s(1+n)(1+2n)(1+3n)/(24n⁴)
        ONE   =  0x1.0000ccp+0f , // ≈  1
        TWEAK =  0x1.6cb8cap-16f  // ≈  0
    ;
    float x = std::bit_cast<float>(
        P0 - (std::bit_cast<int32_t>(a)>>P1)*P2
    );
    float sx = s * x;
    float sAx = sA * x;
    float x2 = x * x;
    float sqrta = std::sqrt(a);
    float x4 = x2 * x2;
    float ax4 = x4 * a;
    float x8 = x4 * x4;
    float y = std::fma( -ax4,x8, ONE );
    float xy = std::fma( x,y, TWEAK );
    float y2 = y * y;
    float sx_sAxy = std::fma( sAx,y, sx );
    float sC_sDy = std::fma( sD,y, sC );
    float sBy = sB * y;
    float sBy_sCy2_sDy3 = std::fma( sC_sDy,y2, sBy );
    float sx_sAxy_sBxy2_sCxy3_sDxy4 = std::fma(
        sBy_sCy2_sDy3,xy, sx_sAxy
    );
    return std::fma( sqrta,sx_sAxy_sBxy2_sCxy3_sDxy4, BIAS );
}
[[nodiscard]] constexpr static float srgb_invgamma(float val) noexcept {
    return val > 0.0031308f ? _helper(val) : 12.92f*val;
}