Fix size_t -> int -> size_t 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)`.

On an implementation side the `min()` is defined for a fixed width
integer type to disambiguate uint from size_t on 32bit platforms,
and yet be able to use it for 32bit operands on 64bit platforms without
upcast.

Fixes 32bit platforms (such as i386) in Debian package build system.

Differential Revision: https://developer.blender.org/D13992

intern/cycles/bvh/embree.cpp

@@ -471,7 +471,7 @@ 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);
@@ -522,7 +522,7 @@ 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();
 
@@ -775,7 +775,7 @@ 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;

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. */

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];

intern/cycles/scene/pointcloud.cpp

@@ -55,7 +55,7 @@ float4 PointCloud::Point::motion_key(const float3 *points,
   /* 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. */
   const float4 curr_key = point_for_step(

intern/cycles/util/math.h

@@ -124,7 +124,12 @@ 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;
 }