hlsl_intrinsic_helpers.h

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//===----- hlsl_intrinsic_helpers.h - HLSL helpers intrinsics -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#ifndef _HLSL_HLSL_INTRINSIC_HELPERS_H_
#define _HLSL_HLSL_INTRINSIC_HELPERS_H_
 
namespace hlsl {
namespace __detail {
 
constexpr int4 d3d_color_to_ubyte4_impl(float4 V) {
  // Use the same scaling factor used by FXC, and DXC for DXIL
  // (i.e., 255.001953)
  // https://github.com/microsoft/DirectXShaderCompiler/blob/070d0d5a2beacef9eeb51037a9b04665716fd6f3/lib/HLSL/HLOperationLower.cpp#L666C1-L697C2
  // The DXC implementation refers to a comment on the following stackoverflow
  // discussion to justify the scaling factor: "Built-in rounding, necessary
  // because of truncation. 0.001953 * 256 = 0.5"
  // https://stackoverflow.com/questions/52103720/why-does-d3dcolortoubyte4-multiplies-components-by-255-001953f
  return V.zyxw * 255.001953f;
}
 
template <typename T> constexpr T length_impl(T X) { return abs(X); }
 
template <typename T, int N>
constexpr enable_if_t<is_same<float, T>::value || is_same<half, T>::value, T>
length_vec_impl(vector<T, N> X) {
#if (__has_builtin(__builtin_spirv_length))
  return __builtin_spirv_length(X);
#else
  return sqrt(dot(X, X));
#endif
}
 
template <typename T>
constexpr vector<T, 4> dst_impl(vector<T, 4> Src0, vector<T, 4> Src1) {
  return {1, Src0[1] * Src1[1], Src0[2], Src1[3]};
}
 
template <typename T> constexpr T distance_impl(T X, T Y) {
  return length_impl(X - Y);
}
 
template <typename T, int N>
constexpr enable_if_t<is_same<float, T>::value || is_same<half, T>::value, T>
distance_vec_impl(vector<T, N> X, vector<T, N> Y) {
  return length_vec_impl(X - Y);
}
 
constexpr float dot2add_impl(half2 a, half2 b, float c) {
#if (__has_builtin(__builtin_dx_dot2add))
  return __builtin_dx_dot2add(a, b, c);
#else
  return dot(a, b) + c;
#endif
}
 
template <typename T, int N>
constexpr enable_if_t<!is_same<double, T>::value, T>
mul_vec_impl(vector<T, N> x, vector<T, N> y) {
  return dot(x, y);
}
 
// Double vectors do not have a dot intrinsic, so expand manually.
template <typename T, int N>
enable_if_t<is_same<double, T>::value, T> mul_vec_impl(vector<T, N> x,
                                                       vector<T, N> y) {
  T sum = x[0] * y[0];
  [unroll] for (int i = 1; i < N; ++i) sum = mad(x[i], y[i], sum);
  return sum;
}
 
template <typename T> constexpr T reflect_impl(T I, T N) {
  return I - 2 * N * I * N;
}
 
template <typename T, int L>
constexpr vector<T, L> reflect_vec_impl(vector<T, L> I, vector<T, L> N) {
#if (__has_builtin(__builtin_spirv_reflect))
  return __builtin_spirv_reflect(I, N);
#else
  return I - 2 * N * dot(I, N);
#endif
}
 
template <typename T, typename U> constexpr T refract_impl(T I, T N, U Eta) {
#if (__has_builtin(__builtin_spirv_refract))
  return __builtin_spirv_refract(I, N, Eta);
#endif
  T Mul = dot(N, I);
  T K = 1 - Eta * Eta * (1 - Mul * Mul);
  T Result = (Eta * I - (Eta * Mul + sqrt(K)) * N);
  return select<T>(K < 0, static_cast<T>(0), Result);
}
 
template <typename T> constexpr T fmod_impl(T X, T Y) {
#if !defined(__DIRECTX__)
  return __builtin_elementwise_fmod(X, Y);
#else
  T div = X / Y;
  bool ge = div >= 0;
  T frc = frac(abs(div));
  return select<T>(ge, frc, -frc) * Y;
#endif
}
 
template <typename T, int N>
constexpr vector<T, N> fmod_vec_impl(vector<T, N> X, vector<T, N> Y) {
#if !defined(__DIRECTX__)
  return __builtin_elementwise_fmod(X, Y);
#else
  vector<T, N> div = X / Y;
  vector<bool, N> ge = div >= 0;
  vector<T, N> frc = frac(abs(div));
  return select<T>(ge, frc, -frc) * Y;
#endif
}
 
template <typename T> constexpr T smoothstep_impl(T Min, T Max, T X) {
#if (__has_builtin(__builtin_spirv_smoothstep))
  return __builtin_spirv_smoothstep(Min, Max, X);
#else
  T S = saturate((X - Min) / (Max - Min));
  return (3 - 2 * S) * S * S;
#endif
}
 
template <typename T, int N>
constexpr vector<T, N> smoothstep_vec_impl(vector<T, N> Min, vector<T, N> Max,
                                           vector<T, N> X) {
#if (__has_builtin(__builtin_spirv_smoothstep))
  return __builtin_spirv_smoothstep(Min, Max, X);
#else
  vector<T, N> S = saturate((X - Min) / (Max - Min));
  return (3 - 2 * S) * S * S;
#endif
}
 
template <typename T> constexpr vector<T, 4> lit_impl(T NDotL, T NDotH, T M) {
  bool DiffuseCond = NDotL < 0;
  T Diffuse = select<T>(DiffuseCond, 0, NDotL);
  vector<T, 4> Result = {1, Diffuse, 0, 1};
  // clang-format off
  bool SpecularCond = or(DiffuseCond, (NDotH < 0));
  // clang-format on
  T SpecularExp = exp(log(NDotH) * M);
  Result[2] = select<T>(SpecularCond, 0, SpecularExp);
  return Result;
}
 
template <typename T> constexpr T faceforward_impl(T N, T I, T Ng) {
  return select(dot(I, Ng) < 0, N, -N);
}
 
template <typename T> constexpr T ldexp_impl(T X, T Exp) {
  return exp2(Exp) * X;
}
 
template <typename K, typename T, int BitWidth>
constexpr K firstbithigh_impl(T X) {
  K FBH = __builtin_hlsl_elementwise_firstbithigh(X);
#if defined(__DIRECTX__)
  // The firstbithigh DXIL ops count bits from the wrong side, so we need to
  // invert it for DirectX.
  K Inversion = (BitWidth - 1) - FBH;
  FBH = select(FBH == -1, FBH, Inversion);
#endif
  return FBH;
}
 
template <typename T> constexpr T ddx_impl(T input) {
#if (__has_builtin(__builtin_spirv_ddx))
  return __builtin_spirv_ddx(input);
#else
  return __builtin_hlsl_elementwise_ddx_coarse(input);
#endif
}
 
template <typename T> constexpr T ddy_impl(T input) {
#if (__has_builtin(__builtin_spirv_ddy))
  return __builtin_spirv_ddy(input);
#else
  return __builtin_hlsl_elementwise_ddy_coarse(input);
#endif
}
 
template <typename T> constexpr T fwidth_impl(T input) {
#if (__has_builtin(__builtin_spirv_fwidth))
  return __builtin_spirv_fwidth(input);
#else
  T derivCoarseX = ddx_coarse(input);
  derivCoarseX = abs(derivCoarseX);
  T derivCoarseY = ddy_coarse(input);
  derivCoarseY = abs(derivCoarseY);
  return derivCoarseX + derivCoarseY;
#endif
}
 
} // namespace __detail
} // namespace hlsl
 
#endif // _HLSL_HLSL_INTRINSIC_HELPERS_H_