https://issues.dlang.org/show_bug.cgi?id=22878

          Issue ID: 22878
           Summary: importC: glibc fallback for HUGE_VAL gives "not
                    representable"
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: duser@neet.fi

// Error: number `1e10000` is not representable
double n = 1e10000;

glibc's math.h defines HUGE_VAL as 1e10000 for old or non-gnu compilers that can't use the builtin:

---
/* Value returned on overflow.  With IEEE 754 floating point, this is
   +Infinity, otherwise the largest representable positive value.  *
#if __GNUC_PREREQ (3, 3)
# define HUGE_VAL (__builtin_huge_val ())
#else
/* This may provoke compiler warnings, and may not be rounded to
   +Infinity in all IEEE 754 rounding modes, but is the best that can
   be done in ISO C while remaining a constant expression.  10,000 is
   greater than the maximum (decimal) exponent for all supported
   floating-point formats and widths.  *
# define HUGE_VAL 1e10000
#endif
---

if using gcc to preprocess, you can get the fallback by undefining the gnu version macros: -U__GNUC__ -U__GNUC_MINOR__ -U__GNUC_PATCHLEVEL__

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