[svn-r10797] Purpose: A feature

Description:  Cygwin compiler doesn't do rounding correctly when converting
"unsigned long long" to "long double".

Solution: Added test case to variable detection of
"hdf5_cv_ullong_to_ldouble_precision_works".

Platforms tested: sleipnir, fuss, and shanti - mainly to test configuration,
don't need to run h5committest.

1 files changed, 40 insertions, 6 deletions

diff --git a/configure b/configure
index 33684ce..4bd8fec 100755
--- a/configure
+++ b/configure
@@ -50273,13 +50273,23 @@ cat >>conftest.$ac_ext <<_ACEOF
 
     int main(void)
     {
+        /* General variables */
+        int endian;
+        int tst_value = 1;
+        int ret = 0;
+
+        /* For FreeBSD */
         unsigned long long l = 0xa601e80bda85fcefULL;
         long double ld;
         unsigned char *c1, *c2;
         size_t size;
-        int endian;
-        int tst_value = 1;
-        int ret = 0;
+
+        /* For Cygwin */
+        unsigned long long l_cyg = 0xfffffffffffffff0ULL;
+        long double ld_cyg;
+        unsigned char *c2_cyg;
+        size_t size_cyg;
+
 
         /* Determine this system's endianess */
         c1 = (unsigned char*)calloc(1, sizeof(int));
@@ -50289,6 +50299,7 @@ cat >>conftest.$ac_ext <<_ACEOF
         else
             endian = 1;  /* big endian */
 
+        /* For FreeBSD */
         size = sizeof(long double);
         memset(&ld, 0, size);
         ld = (long double)l;
@@ -50299,12 +50310,35 @@ cat >>conftest.$ac_ext <<_ACEOF
         /* Test if the last 2 bytes of mantissa are lost.  Mainly for FreeBSD on Intel
          * architecture(sleipnir) where it happens. */
         /*if(endian==0 && c2[0]==0 && c2[1]==0)*/ /*little endian*/
-        if(endian==0 && c2[0]==0) /*little endian*/
+        if(endian==0 && c2[0]==0) { /*little endian*/
+            ret = 1;
+            goto done;
+        }
+
+        /* For Cygwin */
+        size_cyg = sizeof(long double);
+        memset(&ld_cyg, 0, size);
+        ld_cyg = (long double)l_cyg;
+
+        c2_cyg = (unsigned char*)calloc(1, size_cyg);
+        memcpy((void*)c2_cyg, &ld_cyg, size_cyg);
+
+        /* Test if the last 4 bytes(roughly) of mantissa are rounded up.  Mainly for Cygwin
+         * where the values like 0xffffffffffffffff,  0xfffffffffffffffe, ...,
+         * 0xfffffffffffff000 ... are rounded up as 0x0000403f8000000000000000
+         * instead of 0x0000403effffffffffffffff, 0x0000403efffffffffffffffe, ...,
+         * 0x0000403efffffffffffff000 ...
+         */
+        if(endian==0 && c2_cyg[0]==0 && c2_cyg[1]==0 && c2_cyg[2]==0 && c2_cyg[3]==0)
             ret = 1;
 
-        free(c1);
-        free(c2);
 done:
+        if(c1)
+            free(c1);
+        if(c2)
+            free(c2);
+        if(c2_cyg)
+            free(c2_cyg);
         exit(ret);
     }