Fix ComputeModifiedUtf8Hash().

Explicitly cast the character to uint8_t so that we do not
produce different results depending on whether the platform
has a signed or unsigned char.

Test: Additional test in utf_test.
Bug: 120749178
Change-Id: Icf329baa9eb95c2db820b51873e72d95aabf398e

2 files changed, 10 insertions, 2 deletions

diff --git a/libdexfile/dex/utf.cc b/libdexfile/dex/utf.cc
index d09da735f2..ed07568fbc 100644
--- a/libdexfile/dex/utf.cc
+++ b/libdexfile/dex/utf.cc
@@ -194,9 +194,10 @@ int32_t ComputeUtf16HashFromModifiedUtf8(const char* utf8, size_t utf16_length)
 uint32_t ComputeModifiedUtf8Hash(const char* chars) {
   uint32_t hash = 0;
   while (*chars != '\0') {
-    hash = hash * 31 + *chars++;
+    hash = hash * 31 + static_cast<uint8_t>(*chars);
+    ++chars;
   }
-  return static_cast<int32_t>(hash);
+  return hash;
 }
 
 int CompareModifiedUtf8ToUtf16AsCodePointValues(const char* utf8, const uint16_t* utf16,
diff --git a/libdexfile/dex/utf_test.cc b/libdexfile/dex/utf_test.cc
index d2f22d16ef..c7a6a342ff 100644
--- a/libdexfile/dex/utf_test.cc
+++ b/libdexfile/dex/utf_test.cc
@@ -378,4 +378,11 @@ TEST_F(UtfTest, ExhaustiveBidirectionalCodePointCheck) {
   }
 }
 
+TEST_F(UtfTest, NonAscii) {
+  const char kNonAsciiCharacter = '\x80';
+  const char input[] = { kNonAsciiCharacter, '\0' };
+  uint32_t hash = ComputeModifiedUtf8Hash(input);
+  EXPECT_EQ(static_cast<uint8_t>(kNonAsciiCharacter), hash);
+}
+
 }  // namespace art