work in 128-bit integer values while compiling
diff --git a/libasn1parser/asn1p_integer.h b/libasn1parser/asn1p_integer.h
new file mode 100644
index 0000000..7cd6058
--- /dev/null
+++ b/libasn1parser/asn1p_integer.h
@@ -0,0 +1,45 @@
+#ifndef ASN1P_INTEGER_H
+#define ASN1P_INTEGER_H
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif /* HAVE_CONFIG_H */
+
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif /* HAVE_SYS_TYPES_H */
+#ifdef HAVE_INTTYPES_H
+#include <inttypes.h> /* POSIX 1003.1-2001, C99 */
+#else /* HAVE_INTTYPES_H */
+#ifdef HAVE_STDINT_H
+#include <stdint.h> /* SUSv2+ */
+#endif /* HAVE_STDINT_H */
+#endif /* HAVE_INTTYPES_H */
+
+/*
+ * Basic integer type used in numerous places.
+ * ASN.1 does not define any limits on this number, so it must be sufficiently
+ * large to accomodate typical inputs. It does not have to be a dynamically
+ * allocated type with potentially unlimited width: consider the width of
+ * an integer defined here as one of the "compiler limitations".
+ * NOTE: this is NOT a type for ASN.1 "INTEGER" type representation, this
+ * type is used by the compiler itself to handle large integer values
+ * specified inside ASN.1 grammar.
+ */
+#ifdef HAVE_128_BIT_INT
+typedef __int128 asn1c_integer_t;
+#else
+typedef intmax_t asn1c_integer_t;
+#endif
+
+int asn1p_atoi(const char *ptr, asn1c_integer_t *r_value);
+const char *asn1p_itoa(asn1c_integer_t value); /* Ptr to a static buf */
+/*
+ * Return values:
+ * -1: The value did not fit in the buffer.
+ * >0: The length in bytes of the stringified numeric value.
+ */
+int asn1p_itoa_s(char *buf, size_t size,
+ asn1c_integer_t value); /* Return -1 on error, or length. */
+
+#endif /* ASN1P_INTEGER_H */