4 files changed, 52 insertions, 0 deletions
diff --git a/build_config.rb b/build_config.rb
index 3c089d8cc..c54c9d323 100644
--- a/build_config.rb
+++ b/build_config.rb
@@ -23,6 +23,9 @@ MRuby::Build.new do |conf|
   # Use standard Kernel#sprintf method
   conf.gem 'mrbgems/mruby-sprintf'
 
+  # Use extensional String class
+  conf.gem 'mrbgems/mruby-string-ext'
+
   # Generate binaries
   # conf.bins = %w(mrbc mruby mirb)
   
diff --git a/mrbgems/mruby-string-ext/mrbgem.rake b/mrbgems/mruby-string-ext/mrbgem.rake
new file mode 100644
index 000000000..83db97eb4
--- /dev/null
+++ b/mrbgems/mruby-string-ext/mrbgem.rake
@@ -0,0 +1,4 @@
+MRuby::Gem::Specification.new('mruby-string-ext') do |spec|
+  spec.license = 'MIT'
+  spec.authors = 'mruby developers'
+end
diff --git a/mrbgems/mruby-string-ext/src/string.c b/mrbgems/mruby-string-ext/src/string.c
new file mode 100644
index 000000000..175426638
--- /dev/null
+++ b/mrbgems/mruby-string-ext/src/string.c
@@ -0,0 +1,30 @@
+#include "mruby.h"
+#include "mruby/string.h"
+
+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]);
+}
+
+
+void
+mrb_mruby_string_ext_gem_init(mrb_state* mrb)
+{
+  struct RClass * s = mrb->string_class;
+
+  mrb_define_method(mrb, s, "getbyte", mrb_str_getbyte, ARGS_REQ(1));
+}
+
+void
+mrb_mruby_string_ext_gem_final(mrb_state* mrb)
+{
+}
diff --git a/mrbgems/mruby-string-ext/test/string.rb b/mrbgems/mruby-string-ext/test/string.rb
new file mode 100644
index 000000000..9a7579131
--- /dev/null
+++ b/mrbgems/mruby-string-ext/test/string.rb
@@ -0,0 +1,15 @@
+##
+# String(Ext) Test
+
+assert('String#getbyte') do
+  str1 = "hello"
+  bytes1 = [104, 101, 108, 108, 111]
+  assert_equal bytes1[0], str1.getbyte(0)
+  assert_equal bytes1[-1], str1.getbyte(-1)
+  assert_equal bytes1[6], str1.getbyte(6)
+
+  str2 = "\xFF"
+  bytes2 = [0xFF]
+  assert_equal bytes2[0], str2.getbyte(0)
+end
+