Added some missing C99 float operations (#944)

* Added some missing C99 float operations
* Update float.template.mli
* Automatically enable shims on VS 2012 and earlier
* Refactor lib-float test
* Add autoconf test for runnable host exes

When building for Windows, configuring with --build and --host enables
cross-compilation mode but configuring with just --host doesn't (since
the resulting executables can be run on the build machine). Adds an
additional check to see whether executables from the C compiler can be
run _regardless_ of autoconf's cross-compilation mode.

* Workaround broken round on mingw-w64
* Generalise the fma test in configure


Co-authored-by: David Allsopp <david.allsopp@metastack.com>

Changes

@@ -150,6 +150,17 @@ Working version
 
 ### Standard library:
 
+- #944: Add some missing C99 float operations.  `Stdlib` now contains
+  the inverse hyperbolic functions `acosh`, `asinh`, and `atanh`.  These
+  functions were also added to module `Stdlib.Float` together with `exp2`,
+  `log2`, `cbrt`, `erf`, and `erfc`. Full support on MSVC requires VS2013+ but
+  emulated versions are still available (for now) for older compilers.
+  (Markus Mottl, review by David Allsopp, Olivier Andrieu, Florian Angeletti,
+  Nicolás Ojeda Bär, Daniel Bünzli, Fabian @copy, Pascal Cuoq, Damien
+  Doligez, Sébastien Hinderer, Jacques-Henri Jourdan, Xavier Leroy, Guillaume
+  Melquiond, Perry E. Metzger, @objmagic, Gabriel Scherer, Mark Shinwell,
+  Bernhard Schommer and Christophe Troestler)
+
 - #9448: Add String.{empty,cat} as dual of Bytes.{empty,cat},
   String.{of,to}_bytes as aliases of Bytes.{to,of}_string,
   Bytes.split_on_char as dual of String.split_on_char, and binary decoding

INSTALL.adoc

@@ -164,3 +164,12 @@ and sanity checks that could help you pinpoint the problem.
 * On HP 9000/700 machines under HP/UX 9, some versions of `cc` are unable to
   compile correctly the runtime system (wrong code is generated for `(x - y)`
   where `x` is a pointer and `y` an integer). Fix: use `gcc`.
+
+* In the unlikely case that a platform does not offer all C99 float operations
+  that the runtime needs, a configuration error will result.  Users
+  can work around this problem by calling `configure` with the flag
+  `--enable-imprecise-c99-float-ops`.  This will enable simple but potentially
+  imprecise implementations of C99 float operations.  Users with exacting
+  requirements for mathematical accuracy, numerical precision, and proper
+  handling of mathematical corner cases and error conditions may need to
+  consider running their code on a platform with better C99 support.

aclocal.m4

@@ -58,7 +58,8 @@ unknown
 #endif]
     )],
     [AC_CACHE_VAL([ocaml_cv_cc_vendor],
-      [ocaml_cv_cc_vendor=`grep ['^[a-z]'] conftest.i | tr -s ' ' '-'`])],
+      [ocaml_cv_cc_vendor=`grep ['^[a-z]'] conftest.i | tr -s ' ' '-' \
+                                                      | tr -d '\r'`])],
     [AC_MSG_FAILURE([unexpected preprocessor failure])])
   AC_MSG_RESULT([$ocaml_cv_cc_vendor])
 ])
@@ -356,3 +357,115 @@ EOF
 
   OCAML_CC_RESTORE_VARIABLES
 ])
+
+AC_DEFUN([OCAML_HOST_IS_EXECUTABLE], [
+  AC_MSG_CHECKING([whether host executables can be run in the build])
+  old_cross_compiling="$cross_compiling"
+  cross_compiling='no'
+  AC_RUN_IFELSE(
+    [AC_LANG_SOURCE([[int main (void) {return 0;}]])],
+    [AC_MSG_RESULT([yes])
+    host_runnable=true],
+    [AC_MSG_RESULT([no])
+    host_runnable=false],
+    # autoconf displays a warning if this parameter is missing, but
+    # cross-compilation mode was disabled above.
+    [assert=false])
+  cross_compiling="$old_cross_compiling"
+])
+
+# This is AC_RUN_IFELSE but taking $host_runnable into account (i.e. if the
+# program can be run, then it is run)
+AC_DEFUN([OCAML_RUN_IFELSE], [
+  old_cross_compiling="$cross_compiling"
+  AS_IF([test "x$host_runnable" = 'xtrue'], [cross_compiling='no'])
+  AC_RUN_IFELSE([$1],[$2],[$3],[$4])
+  cross_compiling="$old_cross_compiling"
+])
+
+AC_DEFUN([OCAML_C99_CHECK_ROUND], [
+  AC_MSG_CHECKING([whether round works])
+  OCAML_RUN_IFELSE(
+    [AC_LANG_SOURCE([[
+#include <math.h>
+int main (void) {
+  static volatile double d = 0.49999999999999994449;
+  return (fpclassify(round(d)) != FP_ZERO);
+}
+    ]])],
+    [AC_MSG_RESULT([yes])
+    AC_DEFINE([HAS_WORKING_ROUND])],
+    [AC_MSG_RESULT([no])
+    AS_CASE([$enable_imprecise_c99_float_ops,$target],
+      [no,*], [hard_error=true],
+      [yes,*], [hard_error=false],
+      [*,x86_64-w64-mingw32], [hard_error=false],
+      [hard_error=true])
+    AS_IF([test x"$hard_error" = "xtrue"],
+      [AC_MSG_ERROR(m4_normalize([
+        round does not work, enable emulation with
+        --enable-imprecise-c99-float-ops]))],
+      [AC_MSG_WARN(m4_normalize([
+        round does not work; emulation enabled]))])],
+    [AS_CASE([$target],
+      [x86_64-w64-mingw32],[AC_MSG_RESULT([cross-compiling; assume not])],
+      [AC_MSG_RESULT([cross-compiling; assume yes])
+      AC_DEFINE([HAS_WORKING_ROUND])])])
+])
+
+AC_DEFUN([OCAML_C99_CHECK_FMA], [
+  AC_MSG_CHECKING([whether fma works])
+  OCAML_RUN_IFELSE(
+    [AC_LANG_SOURCE([[
+#include <math.h>
+int main (void) {
+  /* Tests 264-266 from testsuite/tests/fma/fma.ml. These tests trigger the
+     broken implementations of Cygwin64, mingw-w64 (x86_64) and VS2013-2017.
+     The static volatile variables aim to thwart GCC's constant folding. */
+  static volatile double x, y, z;
+  double t264, t265, t266;
+  x = 0x3.bd5b7dde5fddap-496;
+  y = 0x3.bd5b7dde5fddap-496;
+  z = -0xd.fc352bc352bap-992;
+  t264 = fma(x, y, z);
+  x = 0x3.bd5b7dde5fddap-504;
+  y = 0x3.bd5b7dde5fddap-504;
+  z = -0xd.fc352bc352bap-1008;
+  t265 = fma(x, y, z);
+  x = 0x8p-540;
+  y = 0x4p-540;
+  z = 0x4p-1076;
+  t266 = fma(x, y, z);
+  return (!(t264 == 0x1.0989687cp-1044 ||
+            t264 == 0x0.000004277ca1fp-1022 || /* Acceptable emulated values */
+            t264 == 0x0.00000428p-1022)
+       || !(t265 == 0x1.0988p-1060 ||
+            t265 == 0x0.0000000004278p-1022 ||  /* Acceptable emulated values */
+            t265 == 0x0.000000000428p-1022)
+       || !(t266 == 0x8p-1076));
+}
+    ]])],
+    [AC_MSG_RESULT([yes])
+    AC_DEFINE([HAS_WORKING_FMA])],
+    [AC_MSG_RESULT([no])
+    AS_CASE([$enable_imprecise_c99_float_ops,$target],
+      [no,*], [hard_error=true],
+      [yes,*], [hard_error=false],
+      [*,x86_64-w64-mingw32|*,x86_64-*-cygwin*], [hard_error=false],
+      [AS_CASE([$ocaml_cv_cc_vendor],
+        [msvc-*], [AS_IF([test "${ocaml_cv_cc_vendor#msvc-}" -lt 1920 ],
+          [hard_error=false],
+          [hard_error=true])],
+        [hard_error=true])])
+    AS_IF([test x"$hard_error" = "xtrue"],
+      [AC_MSG_ERROR(m4_normalize([
+        fma does not work, enable emulation with
+        --enable-imprecise-c99-float-ops]))],
+      [AC_MSG_WARN(m4_normalize([
+        fma does not work; emulation enabled]))])],
+    [AS_CASE([$target],
+      [x86_64-w64-mingw32|x86_64-*-cygwin*],
+        [AC_MSG_RESULT([cross-compiling; assume not])],
+      [AC_MSG_RESULT([cross-compiling; assume yes])
+      AC_DEFINE([HAS_WORKING_FMA])])])
+])