2 files changed, 14 insertions, 8 deletions
diff --git a/spec/ruby/optional/capi/encoding_spec.rb b/spec/ruby/optional/capi/encoding_spec.rb
index e18108c022..ae557b03d7 100644
--- a/spec/ruby/optional/capi/encoding_spec.rb
+++ b/spec/ruby/optional/capi/encoding_spec.rb
@@ -128,10 +128,16 @@ describe "C-API Encoding function" do
 
   describe "rb_enc_mbc_to_codepoint" do
     it "returns the correct codepoint for the given character and size" do
-       @s.rb_enc_mbc_to_codepoint("é", 2).should == 0x00E9
-       @s.rb_enc_mbc_to_codepoint("éa", 2).should == 0x00E9
-       @s.rb_enc_mbc_to_codepoint("éa", 1).should == 0xC3
-       @s.rb_enc_mbc_to_codepoint("éa", 3).should == 0x00E9
+       @s.rb_enc_mbc_to_codepoint("é").should == 0xE9
+    end
+
+    it "returns 0 if p == e" do
+      @s.rb_enc_mbc_to_codepoint("").should == 0
+    end
+
+    it "returns the raw byte if incomplete character in UTF-8" do
+      @s.rb_enc_mbc_to_codepoint("\xC3").should == 0xC3
+      @s.rb_enc_mbc_to_codepoint("\x80").should == 0x80
     end
   end
 
@@ -630,6 +636,7 @@ describe "C-API Encoding function" do
     it "returns the correct case fold for the given string" do
       @s.ONIGENC_MBC_CASE_FOLD("lower").should == ["l", 1]
       @s.ONIGENC_MBC_CASE_FOLD("Upper").should == ["u", 1]
+      @s.ONIGENC_MBC_CASE_FOLD("ABC"[1..-1]).should == ["b", 1]
     end
 
     it "works with other encodings" do
diff --git a/spec/ruby/optional/capi/ext/encoding_spec.c b/spec/ruby/optional/capi/ext/encoding_spec.c
index 68c4161bab..c49f6cde7e 100644
--- a/spec/ruby/optional/capi/ext/encoding_spec.c
+++ b/spec/ruby/optional/capi/ext/encoding_spec.c
@@ -120,10 +120,9 @@ static VALUE encoding_spec_rb_enc_from_index(VALUE self, VALUE index) {
   return rb_str_new2(rb_enc_from_index(NUM2INT(index))->name);
 }
 
-static VALUE encoding_spec_rb_enc_mbc_to_codepoint(VALUE self, VALUE str, VALUE offset) {
-  int o = FIX2INT(offset);
+static VALUE encoding_spec_rb_enc_mbc_to_codepoint(VALUE self, VALUE str) {
   char *p = RSTRING_PTR(str);
-  char *e = p + o;
+  char *e = RSTRING_END(str);
   return INT2FIX(rb_enc_mbc_to_codepoint(p, e, rb_enc_get(str)));
 }
 
@@ -341,7 +340,7 @@ void Init_encoding_spec(void) {
   rb_define_method(cls, "rb_enc_isalnum", encoding_spec_rb_enc_isalnum, 2);
   rb_define_method(cls, "rb_enc_isspace", encoding_spec_rb_enc_isspace, 2);
   rb_define_method(cls, "rb_enc_from_index", encoding_spec_rb_enc_from_index, 1);
-  rb_define_method(cls, "rb_enc_mbc_to_codepoint", encoding_spec_rb_enc_mbc_to_codepoint, 2);
+  rb_define_method(cls, "rb_enc_mbc_to_codepoint", encoding_spec_rb_enc_mbc_to_codepoint, 1);
   rb_define_method(cls, "rb_enc_mbcput", encoding_spec_rb_enc_mbcput, 2);
   rb_define_method(cls, "rb_enc_from_encoding", encoding_spec_rb_enc_from_encoding, 1);
   rb_define_method(cls, "rb_enc_get", encoding_spec_rb_enc_get, 1);