fmath.h: re-inline convert_type() half varieties (#5130)

A few years ago, in PR #3301, we made a big effort to remove Imath types
as much as possible from the public APIs. Somehow, as part of that
refactor, we ended up with just the half-varieties of fmath.h's
convert_types() templates actually being implemented in fmath.cpp and
only declared (by default) in fmath.h. I'm honestly not sure why I did
that now, and the PR doesn't explain that particular point.

But that sets up a potential link incompatibility if OIIO used a
different release of Imath than the use is using when calling that
utility function.

So this PR makes it fully inline again, so the Imath version the
downstream package uses just doesn't need to match what was found/used
at the time that OIIO was built.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/include/OpenImageIO/fmath.h

@@ -911,20 +911,11 @@ convert_type<float,uint8_t> (const float *src, uint8_t *dst, size_t n,
 
 
 #if defined(_HALF_H_) || defined(IMATH_HALF_H_)
+// Specialize for half only if half.h is included prior to fmath.h
 template<>
-OIIO_UTIL_API
-void convert_type<half,float> (const half *src, float *dst, size_t n,
-                               float /*_min*/, float /*_max*/);
-template<>
-OIIO_UTIL_API
-void convert_type<float,half> (const float *src, half *dst, size_t n,
-                               half /*_min*/, half /*_max*/);
-
-#if OIIO_FMATH_HEADER_ONLY
-// Not just the declarations, give the definitions here.
-template<>
-void convert_type<half,float> (const half *src, float *dst, size_t n,
-                               float /*_min*/, float /*_max*/)
+inline void
+convert_type<half,float> (const half *src, float *dst, size_t n,
+                          float /*_min*/, float /*_max*/)
 {
 #if OIIO_SIMD >= 8 && OIIO_F16C_ENABLED
     // If f16c ops are enabled, it's worth doing this by 8's
@@ -944,7 +935,7 @@ void convert_type<half,float> (const half *src, float *dst, size_t n,
 }
 
 template<>
-void
+inline void
 convert_type<float,half> (const float *src, half *dst, size_t n,
                           half /*_min*/, half /*_max*/)
 {
@@ -964,7 +955,6 @@ convert_type<float,half> (const float *src, half *dst, size_t n,
     while (n--)
         *dst++ = *src++;
 }
-#endif /* if OIIO_FMATH_HEADER_ONLY */
 #endif /* if defined(IMATH_HALF_H_) */
 
 #endif /* ifndef __CUDA_ARCH__ */

src/libutil/CMakeLists.txt

@@ -4,7 +4,7 @@
 
 set (libOpenImageIO_Util_srcs argparse.cpp benchmark.cpp
                   errorhandler.cpp farmhash.cpp filesystem.cpp
-                  fmath.cpp filter.cpp hashes.cpp paramlist.cpp
+                  filter.cpp hashes.cpp paramlist.cpp
                   plugin.cpp SHA1.cpp
                   strutil.cpp sysutil.cpp thread.cpp timer.cpp
                   typedesc.cpp ustring.cpp xxhash.cpp)
@@ -15,9 +15,6 @@ if (CMAKE_COMPILER_IS_GNUCC)
 endif ()
 
 if (CMAKE_UNITY_BUILD)
-    # If unity builds are occurring, fmath.cpp MUST be compiled alone. But the
-    # rest can be built together if in group mode.
-    set_property (SOURCE fmath.cpp APPEND PROPERTY SKIP_UNITY_BUILD_INCLUSION TRUE)
     set_source_files_properties (${libOpenImageIO_Util_srcs}
                                  PROPERTIES UNITY_GROUP utilsrc)
 endif ()