BLI: add probabilistic rounding utility

2 files changed, 15 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_rand.hh b/source/blender/blenlib/BLI_rand.hh
index 069a81bb84b..2c4484bd63f 100644
--- a/source/blender/blenlib/BLI_rand.hh
+++ b/source/blender/blenlib/BLI_rand.hh
@@ -103,6 +103,12 @@ class RandomNumberGenerator {
     return float3(rand1, rand2, 1.0f - rand1 - rand2);
   }
 
+  /**
+   * Round value to the next integer randomly.
+   * 4.9f is more likely to round to 5 than 4.6f.
+   */
+  int round_probabilistic(float x);
+
   float2 get_unit_float2();
   float3 get_unit_float3();
   /**
diff --git a/source/blender/blenlib/intern/rand.cc b/source/blender/blenlib/intern/rand.cc
index 27774cad31b..17bf5585f3f 100644
--- a/source/blender/blenlib/intern/rand.cc
+++ b/source/blender/blenlib/intern/rand.cc
@@ -374,6 +374,15 @@ void RandomNumberGenerator::seed_random(uint32_t seed)
   this->seed(seed + hash[seed & 255]);
 }
 
+int RandomNumberGenerator::round_probabilistic(float x)
+{
+  /* Support for negative values can be added when necessary. */
+  BLI_assert(x >= 0.0f);
+  const float round_up_probability = fractf(x);
+  const bool round_up = round_up_probability > this->get_float();
+  return (int)x + (int)round_up;
+}
+
 float2 RandomNumberGenerator::get_unit_float2()
 {
   float a = (float)(M_PI * 2.0) * this->get_float();