modified error system, following suggestions by @nemequ
diff --git a/lib/error_private.h b/lib/error_private.h
new file mode 100644
index 0000000..dbb202f
--- /dev/null
+++ b/lib/error_private.h
@@ -0,0 +1,109 @@
+/* ******************************************************************
+ Error codes and messages
+ Copyright (C) 2013-2016, Yann Collet
+
+ BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are
+ met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above
+ copyright notice, this list of conditions and the following disclaimer
+ in the documentation and/or other materials provided with the
+ distribution.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+ You can contact the author at :
+ - Source repository : https://github.com/Cyan4973/zstd
+****************************************************************** */
+/* Note : this module is expected to remain private, do not expose it */
+
+#ifndef ERROR_H_MODULE
+#define ERROR_H_MODULE
+
+#if defined (__cplusplus)
+extern "C" {
+#endif
+
+
+/* *****************************************
+* Includes
+******************************************/
+#include <stddef.h> /* size_t, ptrdiff_t */
+#include "error_public.h" /* enum list */
+
+
+/* *****************************************
+* Compiler-specific
+******************************************/
+#if defined(__GNUC__)
+# define ERR_STATIC static __attribute__((unused))
+#elif defined (__cplusplus) || (defined (__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L) /* C99 */)
+# define ERR_STATIC static inline
+#elif defined(_MSC_VER)
+# define ERR_STATIC static __inline
+#else
+# define ERR_STATIC static /* this version may generate warnings for unused static functions; disable the relevant warning */
+#endif
+
+
+/* *****************************************
+* Error Codes
+******************************************/
+#define PREFIX(name) ZSTD_error_##name
+
+#ifdef ERROR
+# undef ERROR /* reported already defined on VS 2015 by Rich Geldreich */
+#endif
+#define ERROR(name) (size_t)-PREFIX(name)
+
+ERR_STATIC unsigned ERR_isError(size_t code) { return (code > ERROR(maxCode)); }
+
+
+/* *****************************************
+* Error Strings
+******************************************/
+
+ERR_STATIC const char* ERR_getErrorName(size_t code)
+{
+ static const char* codeError = "Unspecified error code";
+ switch( (size_t)-code )
+ {
+ case ZSTD_error_No_Error: return "No error detected";
+ case ZSTD_error_GENERIC: return "Error (generic)";
+ case ZSTD_error_prefix_unknown: return "Unknown frame descriptor";
+ case ZSTD_error_frameParameter_unsupported: return "Unsupported frame parameter";
+ case ZSTD_error_frameParameter_unsupportedBy32bitsImplementation: return "Frame parameter unsupported in 32-bits mode";
+ case ZSTD_error_init_missing: return "Context should be init first";
+ case ZSTD_error_memory_allocation: return "Allocation error : not enough memory";
+ case ZSTD_error_dstSize_tooSmall: return "Destination buffer is too small";
+ case ZSTD_error_srcSize_wrong: return "Src size incorrect";
+ case ZSTD_error_corruption_detected: return "Corrupted block detected";
+ case ZSTD_error_tableLog_tooLarge: return "tableLog requires too much memory";
+ case ZSTD_error_maxSymbolValue_tooLarge: return "Unsupported max possible Symbol Value : too large";
+ case ZSTD_error_maxSymbolValue_tooSmall: return "Specified maxSymbolValue is too small";
+ case ZSTD_error_maxCode:
+ default: return codeError;
+ }
+}
+
+
+#if defined (__cplusplus)
+}
+#endif
+
+#endif /* ERROR_H_MODULE */