Add support for _Float16 16-bit floating point type

.github/workflows/main.yml

@@ -36,4 +36,3 @@ jobs:
     name: "CMake Workflows"
     uses: ./.github/workflows/cmake.yml
     if: "!contains(github.event.head_commit.message, 'skip-ci')"
-

config/cmake/ConfigureChecks.cmake

@@ -891,7 +891,8 @@ macro (H5ConversionTests TEST def msg)
           ${CMAKE_BINARY_DIR}
           ${HDF_RESOURCES_DIR}/ConversionTests.c
           CMAKE_FLAGS -DCOMPILE_DEFINITIONS:STRING=-D${TEST}_TEST
-          OUTPUT_VARIABLE OUTPUT
+          COMPILE_OUTPUT_VARIABLE ${TEST}_COMPILE_OUTPUT
+          RUN_OUTPUT_VARIABLE ${TEST}_RUN_OUTPUT
       )
       if (${TEST}_COMPILE)
         if (${TEST}_RUN EQUAL "0")
@@ -901,14 +902,17 @@ macro (H5ConversionTests TEST def msg)
           set (${TEST} "" CACHE INTERNAL ${msg})
           message (VERBOSE "${msg}... no")
           file (APPEND ${CMAKE_BINARY_DIR}/CMakeFiles/CMakeError.log
-                "Test ${TEST} Run failed with the following output and exit code:\n ${OUTPUT}\n"
+            "Test ${TEST} Compile succeeded with the following output:\n ${${TEST}_COMPILE_OUTPUT}\n"
+          )         
+          file (APPEND ${CMAKE_BINARY_DIR}/CMakeFiles/CMakeError.log
+            "Test ${TEST} Run failed with exit code ${${TEST}_RUN} and with the following output:\n ${${TEST}_RUN_OUTPUT}\n"
           )
         endif ()
       else ()
         set (${TEST} "" CACHE INTERNAL ${msg})
         message (VERBOSE "${msg}... no")
         file (APPEND ${CMAKE_BINARY_DIR}/CMakeFiles/CMakeError.log
-            "Test ${TEST} Compile failed with the following output:\n ${OUTPUT}\n"
+            "Test ${TEST} Compile failed with the following output:\n ${${TEST}_COMPILE_OUTPUT}\n"
         )
       endif ()
     else ()
@@ -970,3 +974,67 @@ H5ConversionTests (${HDF_PREFIX}_LLONG_TO_LDOUBLE_CORRECT TRUE "Checking IF corr
 # some long double values
 #-----------------------------------------------------------------------------
 H5ConversionTests (${HDF_PREFIX}_DISABLE_SOME_LDOUBLE_CONV FALSE "Checking IF the cpu is power9 and cannot correctly converting long double values")
+
+#-----------------------------------------------------------------------------
+# Check if _Float16 type is available
+#-----------------------------------------------------------------------------
+HDF_CHECK_TYPE_SIZE (_Float16 ${HDF_PREFIX}_SIZEOF__FLOAT16)
+if (${HDF_PREFIX}_SIZEOF__FLOAT16)
+  # Request _Float16 support
+  set (CMAKE_REQUIRED_DEFINITIONS ${CMAKE_REQUIRED_DEFINITIONS} "-D__STDC_WANT_IEC_60559_TYPES_EXT__")
+
+  # Some compilers expose the _Float16 datatype, but not the macros and
+  # functions used with the datatype. We need the macros for proper
+  # datatype conversion support. The main function we're interested in
+  # is fabsf16. Check for these here.
+  CHECK_SYMBOL_EXISTS (FLT16_EPSILON "float.h" h5_have_flt16_epsilon)
+  CHECK_SYMBOL_EXISTS (FLT16_MIN "float.h" h5_have_flt16_min)
+  CHECK_SYMBOL_EXISTS (FLT16_MAX "float.h" h5_have_flt16_max)
+  CHECK_SYMBOL_EXISTS (FLT16_MIN_10_EXP "float.h" h5_have_flt16_min_10_exp)
+  CHECK_SYMBOL_EXISTS (FLT16_MAX_10_EXP "float.h" h5_have_flt16_max_10_exp)
+  CHECK_SYMBOL_EXISTS (FLT16_MANT_DIG "float.h" h5_have_flt16_mant_dig)
+
+  if (h5_have_flt16_epsilon AND h5_have_flt16_min AND
+      h5_have_flt16_max AND h5_have_flt16_min_10_exp AND
+      h5_have_flt16_max_10_exp AND h5_have_flt16_mant_dig)
+    # Some compilers like OneAPI on MSVC appear to just be broken, as support
+    # for _Float16 and its macros can be detected properly, but then code is
+    # generated that uses the __truncsfhf2, __truncdfhf2, __extendhfsf2 functions,
+    # which end up being unresolved with MSVC. Let's try to compile a program
+    # that will generate these functions to check for _Float16 support.
+    message (STATUS "Compiling test program to check for _Float16 support")
+    try_compile (
+        h5_compiled_float16_test
+        ${CMAKE_BINARY_DIR} 
+        ${HDF_RESOURCES_DIR}/HDFTests.c
+        COMPILE_DEFINITIONS "-DCHECK_FLOAT16"
+        C_STANDARD 99
+    )
+
+    if (${h5_compiled_float16_test})
+      # Finally, MacOS 13 appears to have a bug specifically when converting
+      # long double values to _Float16. Release builds of the dt_arith test
+      # would cause any assignments to a _Float16 variable to be elided,
+      # whereas Debug builds would perform incorrect hardware conversions by
+      # simply chopping off all the bytes of the value except for the first 2.
+      # These tests pass on MacOS 14, so let's perform a quick test to check
+      # if the hardware conversion is done correctly.
+      H5ConversionTests (
+          ${HDF_PREFIX}_LDOUBLE_TO_FLOAT16_CORRECT
+          TRUE
+          "Checking if correctly converting long double to _Float16 values"
+      )
+
+      set (${HDF_PREFIX}_HAVE__FLOAT16 1)
+
+      # Check if we can use fabsf16
+      CHECK_FUNCTION_EXISTS (fabsf16 ${HDF_PREFIX}_HAVE_FABSF16)
+    else ()
+      message (STATUS "Failed to compile test program to check for _Float16 support")
+    endif ()
+  else ()
+    set (${HDF_PREFIX}_HAVE__FLOAT16 0)
+  endif ()
+else ()
+  set (${HDF_PREFIX}_HAVE__FLOAT16 0)
+endif ()

config/cmake/ConversionTests.c

@@ -285,3 +285,32 @@ int HDF_NO_UBSAN main(void)
 }
 
 #endif
+
+#ifdef H5_LDOUBLE_TO_FLOAT16_CORRECT_TEST
+
+#define __STDC_WANT_IEC_60559_TYPES_EXT__
+
+#include <stdlib.h>
+#include <float.h>
+#include <math.h>
+#include <limits.h>
+
+int HDF_NO_UBSAN main(void)
+{
+    long double ld;
+    _Float16    half;
+    int         ret = 1;
+
+    ld   = 32.0L;
+    half = 64.0f16;
+
+    half = (_Float16)ld;
+
+    if (fabsl(ld - (long double)half) < LDBL_EPSILON)
+        ret = 0;
+
+done:
+    exit(ret);
+}
+
+#endif

config/cmake/H5pubconf.h.in

@@ -128,6 +128,9 @@
 /* Define if library information should be embedded in the executables */
 #cmakedefine H5_HAVE_EMBEDDED_LIBINFO @H5_HAVE_EMBEDDED_LIBINFO@
 
+/* Define to 1 if you have the `fabsf16' function. */
+#cmakedefine H5_HAVE_FABSF16 @H5_HAVE_FABSF16@
+
 /* Define to 1 if you have the `fcntl' function. */
 #cmakedefine H5_HAVE_FCNTL @H5_HAVE_FCNTL@
 
@@ -140,6 +143,9 @@
 /* Define if support for szip filter is enabled */
 #cmakedefine H5_HAVE_FILTER_SZIP @H5_HAVE_FILTER_SZIP@
 
+/* Determine if _Float16 is available */
+#cmakedefine H5_HAVE__FLOAT16 @H5_HAVE__FLOAT16@
+
 /* Determine if __float128 is available */
 #cmakedefine H5_HAVE_FLOAT128 @H5_HAVE_FLOAT128@
 
@@ -387,6 +393,9 @@
 /* Define if new-style references should be used with dimension scales */
 #cmakedefine H5_DIMENSION_SCALES_WITH_NEW_REF @H5_DIMENSION_SCALES_WITH_NEW_REF@
 
+/* Define if your system can convert long double to _Float16 values correctly. */
+#cmakedefine H5_LDOUBLE_TO_FLOAT16_CORRECT @H5_LDOUBLE_TO_FLOAT16_CORRECT@
+
 /* Define if your system can convert long double to (unsigned) long long
    values correctly. */
 #cmakedefine H5_LDOUBLE_TO_LLONG_ACCURATE @H5_LDOUBLE_TO_LLONG_ACCURATE@
@@ -592,6 +601,9 @@
 /* The size of `_Quad', as computed by sizeof. */
 #define H5_SIZEOF__QUAD @H5_SIZEOF__QUAD@
 
+/* The size of `_Float16', as computed by sizeof. */
+#define H5_SIZEOF__FLOAT16 @H5_SIZEOF__FLOAT16@
+
 /* The size of `__float128', as computed by sizeof. */
 #define H5_SIZEOF___FLOAT128 @H5_SIZEOF___FLOAT128@
 

config/cmake/HDFTests.c

@@ -192,3 +192,36 @@ int main ()
 }
 
 #endif /* HAVE_IOEO */
+
+#ifdef CHECK_FLOAT16
+
+#define __STDC_WANT_IEC_60559_TYPES_EXT__
+#include <float.h>
+
+int
+main(int argc, char **argv)
+{
+    signed char a;
+    _Float16    b;
+    double      c;
+
+    /* Convert signed char to _Float16  */
+    a = 1;
+    b = (_Float16)a;
+
+    /* Convert back */
+    b = 3.0f16;
+    a = (signed char)b;
+
+    /* Convert double to _Float16 */
+    c = 5.0;
+    b = (_Float16)c;
+
+    /* Convert back */
+    b = 3.0f16;
+    c = (double)b;
+
+    return 0;
+}
+
+#endif /* CHECK_FLOAT16 */

configure.ac

@@ -546,6 +546,120 @@ AC_CHECK_SIZEOF([float])
 AC_CHECK_SIZEOF([double])
 AC_CHECK_SIZEOF([long double])
 
+## ----------------------------------------------------------------------
+## Check if _Float16 support is available
+##
+HAVE__FLOAT16="no"
+AC_CHECK_SIZEOF([_Float16])
+if test "$ac_cv_sizeof__Float16" != 0; then
+  # Some compilers expose the _Float16 datatype, but not the macros and
+  # functions used with the datatype. We need the macros for proper
+  # datatype conversion support. The main function we're interested in
+  # is fabsf16. Check for these here.
+  AC_CHECK_DECL([FLT16_EPSILON], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+  AC_CHECK_DECL([FLT16_MIN], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+  AC_CHECK_DECL([FLT16_MAX], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+  AC_CHECK_DECL([FLT16_MIN_10_EXP], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+  AC_CHECK_DECL([FLT16_MAX_10_EXP], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+  AC_CHECK_DECL([FLT16_MANT_DIG], [], [], [[
+                 #define __STDC_WANT_IEC_60559_TYPES_EXT__
+                 #include <float.h>]])
+
+  if test "X$ac_cv_have_decl_FLT16_EPSILON" = "Xyes" &&
+     test "X$ac_cv_have_decl_FLT16_MIN" = "Xyes" &&
+     test "X$ac_cv_have_decl_FLT16_MAX" = "Xyes" &&
+     test "X$ac_cv_have_decl_FLT16_MIN_10_EXP" = "Xyes" &&
+     test "X$ac_cv_have_decl_FLT16_MAX_10_EXP" = "Xyes" &&
+     test "X$ac_cv_have_decl_FLT16_MANT_DIG" = "Xyes" ; then
+    # Some compilers like OneAPI on MSVC appear to just be broken, as support
+    # for _Float16 and its macros can be detected properly, but then code is
+    # generated that uses the __truncsfhf2, __truncdfhf2, __extendhfsf2 functions,
+    # which end up being unresolved with MSVC. Let's try to compile a program
+    # that will generate these functions to check for _Float16 support.
+    AC_MSG_CHECKING([if _Float16 program can be compiled])
+    AC_CACHE_VAL([hdf5_cv_float16_prog_compiled],
+      [AC_RUN_IFELSE(
+        [AC_LANG_PROGRAM([
+            #define __STDC_WANT_IEC_60559_TYPES_EXT__
+            #include <float.h>
+        ],[
+            signed char a;
+            _Float16    b;
+            double      c;
+            /* Convert signed char to _Float16  */
+            a = 1;
+            b = (_Float16)a;
+            /* Convert back */
+            b = 3.0f16;
+            a = (signed char)b;
+            /* Convert double to _Float16 */
+            c = 5.0;
+            b = (_Float16)c;
+            /* Convert back */
+            b = 3.0f16;
+            c = (double)b;
+        ])]
+      , [hdf5_cv_float16_prog_compiled=yes], [hdf5_cv_float16_prog_compiled=no], [hdf5_cv_float16_prog_compiled=no])])
+
+    if test ${hdf5_cv_float16_prog_compiled} = "yes" ; then
+      AC_MSG_RESULT([yes])
+
+      # Finally, MacOS 13 appears to have a bug specifically when converting
+      # long double values to _Float16. Release builds of the dt_arith test
+      # would cause any assignments to a _Float16 variable to be elided,
+      # whereas Debug builds would perform incorrect hardware conversions by
+      # simply chopping off all the bytes of the value except for the first 2.
+      # These tests pass on MacOS 14, so let's perform a quick test to check
+      # if the hardware conversion is done correctly.
+      AC_MSG_CHECKING([if compiler can correctly convert long double values to _Float16])
+      TEST_SRC="`(echo \"#define H5_LDOUBLE_TO_FLOAT16_CORRECT_TEST 1\"; cat $srcdir/config/cmake/ConversionTests.c)`"
+      if test ${ac_cv_sizeof_long_double} = 0; then
+        hdf5_cv_ldouble_to_float16_correct=${hdf5_cv_ldouble_to_float16_correct=no}
+      else
+        AC_CACHE_VAL([hdf5_cv_ldouble_to_float16_correct],
+        [AC_RUN_IFELSE(
+            [AC_LANG_SOURCE([$TEST_SRC])],
+            [hdf5_cv_ldouble_to_float16_correct=yes], [hdf5_cv_ldouble_to_float16_correct=no], [hdf5_cv_ldouble_to_float16_correct=yes])])
+      fi
+
+      if test ${hdf5_cv_ldouble_to_float16_correct} = "yes"; then
+        AC_DEFINE([LDOUBLE_TO_FLOAT16_CORRECT], [1],
+          [Define if your system can convert long double to _Float16 values correctly.])
+        AC_MSG_RESULT([yes])
+      else
+        AC_MSG_RESULT([no])
+      fi
+
+      HAVE__FLOAT16="yes"
+
+      # Check if we can use fabsf16
+      AC_CHECK_FUNC([fabsf16], [AC_DEFINE([HAVE_FABSF16], [1],
+                        [Define if has fabsf16 function])], [])
+
+      # Define HAVE__FLOAT16 macro for H5pubconf.h if _Float16 is available.
+      AC_DEFINE([HAVE__FLOAT16], [1], [Determine if _Float16 is available])
+    else
+      AC_MSG_RESULT([no])
+    fi
+  fi
+
+  AC_MSG_CHECKING([if _Float16 support is available])
+  AC_MSG_RESULT([$HAVE__FLOAT16])
+fi
+
+# Define HAVE__FLOAT16 value to substitute into other files for conditional testing
+AC_SUBST([HAVE__FLOAT16])
+
 ## ----------------------------------------------------------------------
 ## Check if the Fortran interface should be enabled
 ##

doxygen/dox/LearnBasics2.dox

@@ -626,6 +626,11 @@ into a long integer buffer.)
 <th span="3"><strong>Float</strong></th>
 </tr>
 <tr>
+<td>_Float16</td>
+<td>#H5T_NATIVE_FLOAT16</td>
+<td>#H5T_IEEE_F16BE or #H5T_IEEE_F16LE</td>
+</tr>
+<tr>
 <td>float</td>
 <td>#H5T_NATIVE_FLOAT</td>
 <td>#H5T_IEEE_F32BE or #H5T_IEEE_F32LE</td>

doxygen/examples/tables/predefinedDatatypes.dox

@@ -8,6 +8,14 @@
 <th>Description</th>
 </tr>
 <tr>
+<td>#H5T_IEEE_F16BE</td>
+<td>16-bit big-endian IEEE floating point</td>
+</tr>
+<tr>
+<td>#H5T_IEEE_F16LE</td>
+<td>16-bit little-endian IEEE floating point</td>
+</tr>
+<tr>
 <td>#H5T_IEEE_F32BE</td>
 <td>32-bit big-endian IEEE floating point</td>
 </tr>
@@ -465,6 +473,10 @@
 <td>C-style unsigned long long</td>
 </tr>
 <tr>
+<td>#H5T_NATIVE_FLOAT16</td>
+<td>C-style _Float16 (May be H5I_INVALID_HID if platform doesn't support _Float16 type)</td>
+</tr>
+<tr>
 <td>#H5T_NATIVE_FLOAT</td>
 <td>C-style float</td>
 </tr>

hl/src/H5LT.c

@@ -2287,7 +2287,13 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
 
             break;
         case H5T_FLOAT:
-            if (H5Tequal(dtype, H5T_IEEE_F32BE)) {
+            if (H5Tequal(dtype, H5T_IEEE_F16BE)) {
+                snprintf(dt_str, *slen, "H5T_IEEE_F16BE");
+            }
+            else if (H5Tequal(dtype, H5T_IEEE_F16LE)) {
+                snprintf(dt_str, *slen, "H5T_IEEE_F16LE");
+            }
+            else if (H5Tequal(dtype, H5T_IEEE_F32BE)) {
                 snprintf(dt_str, *slen, "H5T_IEEE_F32BE");
             }
             else if (H5Tequal(dtype, H5T_IEEE_F32LE)) {
@@ -2299,6 +2305,11 @@ H5LT_dtype_to_text(hid_t dtype, char *dt_str, H5LT_lang_t lang, size_t *slen, bo
             else if (H5Tequal(dtype, H5T_IEEE_F64LE)) {
                 snprintf(dt_str, *slen, "H5T_IEEE_F64LE");
             }
+#ifdef H5_HAVE__FLOAT16
+            else if (H5Tequal(dtype, H5T_NATIVE_FLOAT16)) {
+                snprintf(dt_str, *slen, "H5T_NATIVE_FLOAT16");
+            }
+#endif
             else if (H5Tequal(dtype, H5T_NATIVE_FLOAT)) {
                 snprintf(dt_str, *slen, "H5T_NATIVE_FLOAT");
             }