[njs] Ensuring that double type is always evaluated at standard precision.

[Dmitry Volyntsev]

details:   https://hg.nginx.org/njs/rev/545d2d21dda5
branches:  
changeset: 1903:545d2d21dda5
user:      Dmitry Volyntsev <xeioex at nginx.com>
date:      Tue Jul 05 22:58:12 2022 -0700
description:
Ensuring that double type is always evaluated at standard precision.

Previously, GCC on x86 uses extended precision for intermediate
calculations by default.  This might conflict with njs_diyfp_t because
GCC is not always rounds back the intermediate values to standard
precision.

The fix is to explicitly tell to a compiler to do so.

This closes #507 issue on Github.

diffstat:

 auto/types |  54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 54 insertions(+), 0 deletions(-)

diffs (61 lines):

diff -r b7c4e0f714a9 -r 545d2d21dda5 auto/types
--- a/auto/types	Tue Jun 28 23:04:00 2022 -0700
+++ b/auto/types	Tue Jul 05 22:58:12 2022 -0700
@@ -118,3 +118,57 @@ njs_feature_test="#include <time.h>
                       return 0;
                   }"
 . auto/feature
+
+
+# Ensuring that double type is always evaluated at standard
+# precision required by njs_diyfp_t
+
+
+case $NJS_CC_NAME in
+
+    gcc)
+        NJS_CFLAGS="$NJS_CFLAGS -fexcess-precision=standard"
+    ;;
+
+    clang)
+
+        njs_found=no
+
+        njs_feature="flag -ffp-eval-method=double"
+        njs_feature_name=NJS_HAVE_FP_EVAL_METHOD
+        njs_feature_run=no
+        njs_feature_incs="-ffp-eval-method=double"
+        njs_feature_libs=
+        njs_feature_test="int main(void) {
+                             return 0;
+                         }"
+
+        . auto/feature
+
+        if [ $njs_found = yes ]; then
+            NJS_CFLAGS="$NJS_CFLAGS -ffp-eval-method=double"
+        fi
+
+    ;;
+
+    SunC)
+
+        njs_found=no
+
+        njs_feature="flag -xarch=sse2"
+        njs_feature_name=NJS_HAVE_XARCH_SSE2
+        njs_feature_run=no
+        njs_feature_incs="-xarch=sse2"
+        njs_feature_libs=
+        njs_feature_test="int main(void) {
+                             return 0;
+                         }"
+
+        . auto/feature
+
+        if [ $njs_found = yes ]; then
+            NJS_CFLAGS="$NJS_CFLAGS -xarch=sse2"
+        fi
+    ;;
+
+esac