lcg.h

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/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
 *
 * SPDX-License-Identifier: Apache-2.0 */
 
#pragma once
 
#include "util/hash.h"
 
CCL_NAMESPACE_BEGIN
 
/* Linear Congruential Generator */
 
/* This is templated to handle multiple address spaces on Metal. */
template<class T> ccl_device uint lcg_step_uint(T rng)
{
  /* implicit mod 2^32 */
  *rng = (1103515245 * (*rng) + 12345);
  return *rng;
}
 
/* This is templated to handle multiple address spaces on Metal. */
template<class T> ccl_device float lcg_step_float(T rng)
{
  /* implicit mod 2^32 */
  *rng = (1103515245 * (*rng) + 12345);
  return (float)*rng * (1.0f / (float)0xFFFFFFFF);
}
 
template<class T> ccl_device float3 lcg_step_float3(T rng)
{
  /* Make sure the random numbers are evaluated in order. */
  const float rand_x = lcg_step_float(rng);
  const float rand_y = lcg_step_float(rng);
  const float rand_z = lcg_step_float(rng);
  return make_float3(rand_x, rand_y, rand_z);
}
 
ccl_device uint lcg_init(const uint seed)
{
  uint rng = seed;
  lcg_step_uint(&rng);
  return rng;
}
 
ccl_device_inline uint lcg_state_init(const uint rng_hash,
                                      const uint rng_offset,
                                      const uint sample,
                                      const uint scramble)
{
  return hash_uint3(rng_hash ^ scramble, rng_offset, sample);
}
 
CCL_NAMESPACE_END