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  • /* SPDX-FileCopyrightText: 2022-2023 Blender Authors
    
     *
     * SPDX-License-Identifier: Apache-2.0 */
    
    
    /** \file
     * \ingroup mikktspace
     */
    
    #pragma once
    
    #include <cassert>
    #include <cmath>
    
    #ifndef M_PI_F
    #  define M_PI_F (3.1415926535897932f) /* pi */
    #endif
    
    namespace mikk {
    
    inline bool not_zero(const float fX)
    {
      return fabsf(fX) > FLT_MIN;
    }
    
    /* Helpers for (un)packing a 2-bit vertex index and a 30-bit face index to one integer. */
    static uint pack_index(const uint face, const uint vert)
    {
      assert((vert & 0x3) == vert);
      return (face << 2) | (vert & 0x3);
    }
    
    static void unpack_index(uint &face, uint &vert, const uint indexIn)
    {
      vert = indexIn & 0x3;
      face = indexIn >> 2;
    }
    
    /* From intern/cycles/util/math_fast.h */
    inline float fast_acosf(float x)
    {
      const float f = fabsf(x);
      /* clamp and crush denormals. */
      const float m = (f < 1.0f) ? 1.0f - (1.0f - f) : 1.0f;
      /* Based on http://www.pouet.net/topic.php?which=9132&page=2
    
       * 85% accurate (ULP 0)
    
       * Examined 2130706434 values of acos:
    
       *   15.2000597 avg ULP diff, 4492 max ULP, 4.51803e-05 max error // without "denormal crush"
    
       * Examined 2130706434 values of acos:
    
       *   15.2007108 avg ULP diff, 4492 max ULP, 4.51803e-05 max error // with "denormal crush"
    
       */
      const float a = sqrtf(1.0f - m) *
                      (1.5707963267f + m * (-0.213300989f + m * (0.077980478f + m * -0.02164095f)));
      return x < 0 ? M_PI_F - a : a;
    }
    
    static uint rotl(uint x, uint k)
    {
      return (x << k) | (x >> (32 - k));
    }
    
    static uint hash_uint3(uint kx, uint ky, uint kz)
    {
      uint a, b, c;
      a = b = c = 0xdeadbeef + (2 << 2) + 13;
    
      c += kz;
      b += ky;
      a += kx;
    
      c = (c ^ b) - rotl(b, 14);
      a = (a ^ c) - rotl(c, 11);
      b = (b ^ a) - rotl(a, 25);
      c = (c ^ b) - rotl(b, 16);
    
      return c;
    }
    
    static uint hash_uint3_fast(const uint x, const uint y, const uint z)
    {
      return (x * 73856093) ^ (y * 19349663) ^ (z * 83492791);
    }
    
    static uint float_as_uint(const float v)
    {
      return *((uint *)(&v));
    }
    
    static float uint_as_float(const uint v)
    {
      return *((float *)(&v));
    }
    
    static uint hash_float3_fast(const float x, const float y, const float z)
    {
      return hash_uint3_fast(float_as_uint(x), float_as_uint(y), float_as_uint(z));
    }
    
    static uint hash_float3x3(const float3 &x, const float3 &y, const float3 &z)
    {
      return hash_uint3(hash_float3_fast(x.x, x.y, x.z),
                        hash_float3_fast(y.x, y.y, y.z),
                        hash_float3_fast(z.x, z.y, z.z));
    }
    
    template<typename T, typename KeyGetter>
    void radixsort(std::vector<T> &data, std::vector<T> &data2, KeyGetter getKey)
    {
      typedef decltype(getKey(data[0])) key_t;
      constexpr size_t datasize = sizeof(key_t);
      static_assert(datasize % 2 == 0);
      static_assert(std::is_integral<key_t>::value);
    
    
      uint bins[datasize][257] = {{0}};
    
    
      /* Count number of elements per bin. */
      for (const T &item : data) {
        key_t key = getKey(item);
        for (uint pass = 0; pass < datasize; pass++)
          bins[pass][((key >> (8 * pass)) & 0xff) + 1]++;
      }
    
      /* Compute prefix sum to find position of each bin in the sorted array. */
      for (uint pass = 0; pass < datasize; pass++) {
        for (uint i = 2; i < 256; i++) {
          bins[pass][i] += bins[pass][i - 1];
        }
      }
    
      int shift = 0;
      for (uint pass = 0; pass < datasize; pass++, shift += 8) {
        /* Insert the elements in their correct location based on their bin. */
        for (const T &item : data) {
          uint pos = bins[pass][(getKey(item) >> shift) & 0xff]++;
          data2[pos] = item;
        }
    
        /* Swap arrays. */
        std::swap(data, data2);
      }
    }
    
    static void float_add_atomic(float *val, float add)
    {
    
      /* Hacky, but atomic floats are only supported from C++20 onward.
       * This works in practice since `std::atomic<uint32_t>` is really just an `uint32_t` in memory,
    
       * so this cast lets us do a 32-bit CAS operation (which is used to build the atomic float
       * operation) without needing any external libraries or compiler-specific builtins. */
      std::atomic<uint32_t> *atomic_val = reinterpret_cast<std::atomic<uint32_t> *>(val);
      for (;;) {
        uint32_t old_v = atomic_val->load();
        uint32_t new_v = float_as_uint(uint_as_float(old_v) + add);
        if (atomic_val->compare_exchange_weak(old_v, new_v)) {
          return;
        }
      }
    }
    
    }  // namespace mikk