split internal.h into files

One day, I could not resist the way it was written.  I finally started
to make the code clean.  This changeset is the beginning of a series of
housekeeping commits.  It is a simple refactoring; split internal.h into
files, so that we can divide and concur in the upcoming commits.  No
lines of codes are either added or removed, except the obvious file
headers/footers.  The generated binary is identical to the one before.

internal/compar.h

@@ -0,0 +1,54 @@
+#ifndef INTERNAL_COMPAR_H /* -*- C -*- */
+#define INTERNAL_COMPAR_H
+/**
+ * @file
+ * @brief      Internal header for Comparable.
+ * @author     \@shyouhei
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ */
+
+#define STRING_P(s) (RB_TYPE_P((s), T_STRING) && CLASS_OF(s) == rb_cString)
+
+#ifdef RUBY_INTEGER_UNIFICATION
+# define rb_cFixnum rb_cInteger
+# define rb_cBignum rb_cInteger
+#endif
+
+enum {
+    cmp_opt_Fixnum,
+    cmp_opt_String,
+    cmp_opt_Float,
+    cmp_optimizable_count
+};
+
+struct cmp_opt_data {
+    unsigned int opt_methods;
+    unsigned int opt_inited;
+};
+
+#define NEW_CMP_OPT_MEMO(type, value) \
+    NEW_PARTIAL_MEMO_FOR(type, value, cmp_opt)
+#define CMP_OPTIMIZABLE_BIT(type) (1U << TOKEN_PASTE(cmp_opt_,type))
+#define CMP_OPTIMIZABLE(data, type) \
+    (((data).opt_inited & CMP_OPTIMIZABLE_BIT(type)) ? \
+     ((data).opt_methods & CMP_OPTIMIZABLE_BIT(type)) : \
+     (((data).opt_inited |= CMP_OPTIMIZABLE_BIT(type)), \
+      rb_method_basic_definition_p(TOKEN_PASTE(rb_c,type), id_cmp) && \
+      ((data).opt_methods |= CMP_OPTIMIZABLE_BIT(type))))
+
+#define OPTIMIZED_CMP(a, b, data) \
+    ((FIXNUM_P(a) && FIXNUM_P(b) && CMP_OPTIMIZABLE(data, Fixnum)) ? \
+     (((long)a > (long)b) ? 1 : ((long)a < (long)b) ? -1 : 0) : \
+     (STRING_P(a) && STRING_P(b) && CMP_OPTIMIZABLE(data, String)) ? \
+     rb_str_cmp(a, b) : \
+     (RB_FLOAT_TYPE_P(a) && RB_FLOAT_TYPE_P(b) && CMP_OPTIMIZABLE(data, Float)) ? \
+     rb_float_cmp(a, b) : \
+     rb_cmpint(rb_funcallv(a, id_cmp, 1, &b), a, b))
+
+/* compar.c */
+VALUE rb_invcmp(VALUE, VALUE);
+
+#endif /* INTERNAL_COMPAR_H */