Move String#{getbyte,setbyte,byteslice} to the core; #4696

Unlike CRuby, there's no way to process strings byte-wise by core
methods because there's no per string encoding in mruby, so that
we moved 3 byte-wise operation methods from `mruby-string-ext` gem.

src/string.c

@@ -2941,6 +2941,104 @@ mrb_str_bytes(mrb_state *mrb, mrb_value str)
   return a;
 }
 
+/*
+ *  call-seq:
+ *     str.getbyte(index)          -> 0 .. 255
+ *
+ *  returns the <i>index</i>th byte as an integer.
+ */
+static mrb_value
+mrb_str_getbyte(mrb_state *mrb, mrb_value str)
+{
+  mrb_int pos;
+  mrb_get_args(mrb, "i", &pos);
+
+  if (pos < 0)
+    pos += RSTRING_LEN(str);
+  if (pos < 0 ||  RSTRING_LEN(str) <= pos)
+    return mrb_nil_value();
+
+  return mrb_fixnum_value((unsigned char)RSTRING_PTR(str)[pos]);
+}
+
+/*
+ *  call-seq:
+ *     str.setbyte(index, integer) -> integer
+ *
+ *  modifies the <i>index</i>th byte as <i>integer</i>.
+ */
+static mrb_value
+mrb_str_setbyte(mrb_state *mrb, mrb_value str)
+{
+  mrb_int pos, byte;
+  mrb_int len;
+
+  mrb_get_args(mrb, "ii", &pos, &byte);
+
+  len = RSTRING_LEN(str);
+  if (pos < -len || len <= pos)
+    mrb_raisef(mrb, E_INDEX_ERROR, "index %i out of string", pos);
+  if (pos < 0)
+    pos += len;
+
+  mrb_str_modify(mrb, mrb_str_ptr(str));
+  byte &= 0xff;
+  RSTRING_PTR(str)[pos] = (unsigned char)byte;
+  return mrb_fixnum_value((unsigned char)byte);
+}
+
+/*
+ *  call-seq:
+ *     str.byteslice(integer)           -> new_str or nil
+ *     str.byteslice(integer, integer)   -> new_str or nil
+ *     str.byteslice(range)            -> new_str or nil
+ *
+ *  Byte Reference---If passed a single Integer, returns a
+ *  substring of one byte at that position. If passed two Integer
+ *  objects, returns a substring starting at the offset given by the first, and
+ *  a length given by the second. If given a Range, a substring containing
+ *  bytes at offsets given by the range is returned. In all three cases, if
+ *  an offset is negative, it is counted from the end of <i>str</i>. Returns
+ *  <code>nil</code> if the initial offset falls outside the string, the length
+ *  is negative, or the beginning of the range is greater than the end.
+ *  The encoding of the resulted string keeps original encoding.
+ *
+ *     "hello".byteslice(1)     #=> "e"
+ *     "hello".byteslice(-1)    #=> "o"
+ *     "hello".byteslice(1, 2)  #=> "el"
+ *     "\x80\u3042".byteslice(1, 3) #=> "\u3042"
+ *     "\x03\u3042\xff".byteslice(1..3) #=> "\u3042"
+ */
+static mrb_value
+mrb_str_byteslice(mrb_state *mrb, mrb_value str)
+{
+  mrb_value a1, a2;
+  mrb_int str_len = RSTRING_LEN(str), beg, len;
+  mrb_bool empty = TRUE;
+
+  if (mrb_get_args(mrb, "o|o", &a1, &a2) == 2) {
+    beg = mrb_fixnum(mrb_to_int(mrb, a1));
+    len = mrb_fixnum(mrb_to_int(mrb, a2));
+  }
+  else if (mrb_type(a1) == MRB_TT_RANGE) {
+    if (mrb_range_beg_len(mrb, a1, &beg, &len, str_len, TRUE) != MRB_RANGE_OK) {
+      return mrb_nil_value();
+    }
+  }
+  else {
+    beg = mrb_fixnum(mrb_to_int(mrb, a1));
+    len = 1;
+    empty = FALSE;
+  }
+
+  if (mrb_str_beg_len(str_len, &beg, &len) && (empty || len != 0)) {
+    return mrb_str_byte_subseq(mrb, str, beg, len);
+  }
+  else {
+    return mrb_nil_value();
+  }
+}
+
 /* ---------------------------*/
 void
 mrb_init_string(mrb_state *mrb)
@@ -2998,6 +3096,10 @@ mrb_init_string(mrb_state *mrb)
   mrb_define_method(mrb, s, "upcase!",         mrb_str_upcase_bang,     MRB_ARGS_NONE()); /* 15.2.10.5.43 */
   mrb_define_method(mrb, s, "inspect",         mrb_str_inspect,         MRB_ARGS_NONE()); /* 15.2.10.5.46(x) */
   mrb_define_method(mrb, s, "bytes",           mrb_str_bytes,           MRB_ARGS_NONE());
+
+  mrb_define_method(mrb, s, "getbyte",         mrb_str_getbyte,         MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, s, "setbyte",         mrb_str_setbyte,         MRB_ARGS_REQ(2));
+  mrb_define_method(mrb, s, "byteslice",       mrb_str_byteslice,       MRB_ARGS_REQ(1)|MRB_ARGS_OPT(1));
 }
 
 #ifndef MRB_WITHOUT_FLOAT