From: Sergey Sharybin <sergey@blender.org>
Date: Wed, 2 Feb 2022 11:17:13 +0100
Subject: fix_round_trip_in_Cycles

There are two things achieved by this change:

- No possible downcast of size_t to int when calculating motion steps.
- Disambiguate call to min() which was for some reason considered
  ambiguous on 32bit platforms `min(int, unsigned int)`.

Differential Revision: https://developer.blender.org/D13992
---
 intern/cycles/bvh/embree.cpp | 6 +++---
 intern/cycles/scene/hair.cpp | 8 ++++----
 intern/cycles/scene/mesh.cpp | 2 +-
 intern/cycles/util/math.h    | 7 ++++++-
 4 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/intern/cycles/bvh/embree.cpp b/intern/cycles/bvh/embree.cpp
index 944a84c..386c6f4 100644
--- a/intern/cycles/bvh/embree.cpp
+++ b/intern/cycles/bvh/embree.cpp
@@ -418,7 +418,7 @@ void BVHEmbree::add_instance(Object *ob, int i)
   assert(instance_bvh != NULL);
 
   const size_t num_object_motion_steps = ob->use_motion() ? ob->get_motion().size() : 1;
-  const size_t num_motion_steps = min(num_object_motion_steps, RTC_MAX_TIME_STEP_COUNT);
+  const size_t num_motion_steps = min(num_object_motion_steps, (size_t)RTC_MAX_TIME_STEP_COUNT);
   assert(num_object_motion_steps <= RTC_MAX_TIME_STEP_COUNT);
 
   RTCGeometry geom_id = rtcNewGeometry(rtc_device, RTC_GEOMETRY_TYPE_INSTANCE);
@@ -469,7 +469,7 @@ void BVHEmbree::add_triangles(const Object *ob, const Mesh *mesh, int i)
   }
 
   assert(num_motion_steps <= RTC_MAX_TIME_STEP_COUNT);
-  num_motion_steps = min(num_motion_steps, RTC_MAX_TIME_STEP_COUNT);
+  num_motion_steps = min(num_motion_steps, (size_t)RTC_MAX_TIME_STEP_COUNT);
 
   const size_t num_triangles = mesh->num_triangles();
 
@@ -638,7 +638,7 @@ void BVHEmbree::add_curves(const Object *ob, const Hair *hair, int i)
   }
 
   assert(num_motion_steps <= RTC_MAX_TIME_STEP_COUNT);
-  num_motion_steps = min(num_motion_steps, RTC_MAX_TIME_STEP_COUNT);
+  num_motion_steps = min(num_motion_steps, (size_t)RTC_MAX_TIME_STEP_COUNT);
 
   const size_t num_curves = hair->num_curves();
   size_t num_segments = 0;
diff --git a/intern/cycles/scene/hair.cpp b/intern/cycles/scene/hair.cpp
index 2951a60..0fd9c70 100644
--- a/intern/cycles/scene/hair.cpp
+++ b/intern/cycles/scene/hair.cpp
@@ -119,7 +119,7 @@ void Hair::Curve::motion_keys(const float3 *curve_keys,
 {
   /* Figure out which steps we need to fetch and their interpolation factor. */
   const size_t max_step = num_steps - 1;
-  const size_t step = min((int)(time * max_step), max_step - 1);
+  const size_t step = std::min((size_t)(time * max_step), max_step - 1);
   const float t = time * max_step - step;
   /* Fetch vertex coordinates. */
   float4 curr_keys[2];
@@ -147,7 +147,7 @@ void Hair::Curve::cardinal_motion_keys(const float3 *curve_keys,
 {
   /* Figure out which steps we need to fetch and their interpolation factor. */
   const size_t max_step = num_steps - 1;
-  const size_t step = min((int)(time * max_step), max_step - 1);
+  const size_t step = min((size_t)(time * max_step), max_step - 1);
   const float t = time * max_step - step;
   /* Fetch vertex coordinates. */
   float4 curr_keys[4];
@@ -192,7 +192,7 @@ void Hair::Curve::keys_for_step(const float3 *curve_keys,
                                 float4 r_keys[2]) const
 {
   k0 = max(k0, 0);
-  k1 = min(k1, num_keys - 1);
+  k1 = min(k1, (size_t)(num_keys - 1));
   const size_t center_step = ((num_steps - 1) / 2);
   if (step == center_step) {
     /* Center step: regular key location. */
@@ -238,7 +238,7 @@ void Hair::Curve::cardinal_keys_for_step(const float3 *curve_keys,
                                          float4 r_keys[4]) const
 {
   k0 = max(k0, 0);
-  k3 = min(k3, num_keys - 1);
+  k3 = min(k3, (size_t)(num_keys - 1));
   const size_t center_step = ((num_steps - 1) / 2);
   if (step == center_step) {
     /* Center step: regular key location. */
diff --git a/intern/cycles/scene/mesh.cpp b/intern/cycles/scene/mesh.cpp
index f47dab3..e6c8d9b 100644
--- a/intern/cycles/scene/mesh.cpp
+++ b/intern/cycles/scene/mesh.cpp
@@ -53,7 +53,7 @@ void Mesh::Triangle::motion_verts(const float3 *verts,
 {
   /* Figure out which steps we need to fetch and their interpolation factor. */
   const size_t max_step = num_steps - 1;
-  const size_t step = min((int)(time * max_step), max_step - 1);
+  const size_t step = min((size_t)(time * max_step), max_step - 1);
   const float t = time * max_step - step;
   /* Fetch vertex coordinates. */
   float3 curr_verts[3];
diff --git a/intern/cycles/util/math.h b/intern/cycles/util/math.h
index e4c7df6..4e0e97f 100644
--- a/intern/cycles/util/math.h
+++ b/intern/cycles/util/math.h
@@ -122,7 +122,12 @@ ccl_device_inline int min(int a, int b)
   return (a < b) ? a : b;
 }
 
-ccl_device_inline uint min(uint a, uint b)
+ccl_device_inline uint32_t min(uint32_t a, uint32_t b)
+{
+  return (a < b) ? a : b;
+}
+
+ccl_device_inline uint64_t min(uint64_t a, uint64_t b)
 {
   return (a < b) ? a : b;
 }
