# File lib/mkmf.rb, line 373
def try_constant(const, headers = nil, opt = "", &b)
  includes = cpp_include(headers)
  if CROSS_COMPILING
    if try_static_assert("#{const} > 0", headers, opt)
      # positive constant
    elsif try_static_assert("#{const} < 0", headers, opt)
      neg = true
      const = "-(#{const})"
    elsif try_static_assert("#{const} == 0", headers, opt)
      return 0
    else
      # not a constant
      return nil
    end
    upper = 1
    lower = 0
    until try_static_assert("#{const} <= #{upper}", headers, opt)
      lower = upper
      upper <<= 1
    end
    return nil unless lower
    while upper > lower + 1
      mid = (upper + lower) / 2
      if try_static_assert("#{const} > #{mid}", headers, opt)
        lower = mid
      else
        upper = mid
      end
    end
    upper = -upper if neg
    return upper
  else
    src = %{#{COMMON_HEADERS}
#{includes}
#include <stdio.h>
/*top*/
int conftest_const = (int)(#{const});
int main() {printf("%d\\n", conftest_const); return 0;}
}
    if try_link0(src, opt, &b)
      xpopen("./conftest") do |f|
        return Integer(f.gets)
      end
    end
  end
  nil
end