[libc-commits] [libc] [libc] Implemented mblen functions (PR #150141)

via libc-commits libc-commits at lists.llvm.org
Thu Jul 24 10:17:40 PDT 2025 

https://github.com/sribee8 updated https://github.com/llvm/llvm-project/pull/150141

>From 69768eb6dbc63755abf8140d2584edc4f91928f5 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Tue, 22 Jul 2025 21:43:27 +0000
Subject: [PATCH 1/5] implemented mblen

---
 libc/config/linux/x86_64/entrypoints.txt |   1 +
 libc/include/wchar.yaml                  |   7 ++
 libc/src/wchar/CMakeLists.txt            |  16 ++++
 libc/src/wchar/mblen.cpp                 |  38 ++++++++
 libc/src/wchar/mblen.h                   |  21 +++++
 libc/src/wchar/mbrlen.cpp                |  38 ++++++++
 libc/src/wchar/mbrlen.h                  |  22 +++++
 libc/test/src/wchar/CMakeLists.txt       |  13 +++
 libc/test/src/wchar/mblen_test.cpp       | 105 +++++++++++++++++++++++
 9 files changed, 261 insertions(+)
 create mode 100644 libc/src/wchar/mblen.cpp
 create mode 100644 libc/src/wchar/mblen.h
 create mode 100644 libc/src/wchar/mbrlen.cpp
 create mode 100644 libc/src/wchar/mbrlen.h
 create mode 100644 libc/test/src/wchar/mblen_test.cpp

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 381359cec6f1d..5610c946a90fb 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1261,6 +1261,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.sys.socket.recvmsg
 
     # wchar.h entrypoints
+    libc.src.wchar.mblen
     libc.src.wchar.mbrtowc
     libc.src.wchar.mbtowc
     libc.src.wchar.wcrtomb
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 123d3440aeec3..605e505dc3bc7 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -53,6 +53,13 @@ functions:
       - type: wchar_t *__restrict
       - type: const char *__restrict
       - type: size_t
+  - name: mblen
+    standards:
+      - stdc
+    return_type: int
+    arguments:
+      - type: const char *__restrict
+      - type: size_t
   - name: wmemset
     standards:
       - stdc
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index 7ace1a6ca66ba..5bc294eeec587 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -159,6 +159,22 @@ add_entrypoint_object(
     libc.src.__support.wchar.mbstate
 )
 
+add_entrypoint_object(
+  mblen
+  SRCS
+    mblen.cpp
+  HDRS
+    mblen.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.wchar_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbrtowc
+    libc.src.__support.wchar.mbstate
+)
+
 add_entrypoint_object(
   wmemset
   SRCS
diff --git a/libc/src/wchar/mblen.cpp b/libc/src/wchar/mblen.cpp
new file mode 100644
index 0000000000000..0f7b94dcf7ca5
--- /dev/null
+++ b/libc/src/wchar/mblen.cpp
@@ -0,0 +1,38 @@
+//===-- Implementation of mblen -------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/wchar/mblen.h"
+
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, mblen, (const char *__restrict s, size_t n)) {
+  // returns 0 since UTF-8 encoding is not state-dependent
+  if (s == nullptr)
+    return 0;
+  internal::mbstate internal_mbstate;
+  // temp ptr to use for internal function
+  wchar_t buf[1];
+  auto ret = internal::mbrtowc(buf, s, n, &internal_mbstate);
+  if (!ret.has_value() || static_cast<int>(ret.value()) == -2) {
+    // Encoding failure
+    if (!ret.has_value())
+      libc_errno = EILSEQ;
+    return -1;
+  }
+  return static_cast<int>(ret.value());
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/mblen.h b/libc/src/wchar/mblen.h
new file mode 100644
index 0000000000000..982081270cf9a
--- /dev/null
+++ b/libc/src/wchar/mblen.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for mblen -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_WCHAR_MBLEN_H
+#define LLVM_LIBC_SRC_WCHAR_MBLEN_H
+
+#include "hdr/types/size_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+int mblen(const char *__restrict s, size_t n);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBLEN_H
diff --git a/libc/src/wchar/mbrlen.cpp b/libc/src/wchar/mbrlen.cpp
new file mode 100644
index 0000000000000..0a256f8d50102
--- /dev/null
+++ b/libc/src/wchar/mbrlen.cpp
@@ -0,0 +1,38 @@
+//===-- Implementation of mbrlen ------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/wchar/mbrlen.h"
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "hdr/types/wchar_t.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/wchar/mbrtowc.h"
+#include "src/__support/wchar/mbstate.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(size_t, mbrlen,
+                   (const char *__restrict s, size_t n,
+                    mbstate_t *__restrict ps)) {
+  static internal::mbstate internal_mbstate;
+  auto ret = internal::mbrtowc(pwc, s, n,
+                               ps == nullptr
+                                   ? &internal_mbstate
+                                   : reinterpret_cast<internal::mbstate *>(ps));
+  if (!ret.has_value()) {
+    // Encoding failure
+    libc_errno = ret.error();
+    return -1;
+  }
+  return ret.value();
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/wchar/mbrlen.h b/libc/src/wchar/mbrlen.h
new file mode 100644
index 0000000000000..08b59cfc8651c
--- /dev/null
+++ b/libc/src/wchar/mbrlen.h
@@ -0,0 +1,22 @@
+//===-- Implementation header for mbrlen ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_WCHAR_MBRLEN_H
+#define LLVM_LIBC_SRC_WCHAR_MBRLEN_H
+
+#include "hdr/types/mbstate_t.h"
+#include "hdr/types/size_t.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+size_t mbrlen(const char *__restrict s, size_t n, mbstate_t *__restrict ps);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_WCHAR_MBRLEN_H
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index 176cf7c3487cd..de0cd697b3a02 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -64,6 +64,19 @@ add_libc_test(
     libc.test.UnitTest.ErrnoCheckingTest
 )
 
+add_libc_test(
+  mblen_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    mblen_test.cpp
+  DEPENDS
+    libc.src.__support.libc_errno
+    libc.src.wchar.mblen
+    libc.hdr.types.wchar_t
+    libc.test.UnitTest.ErrnoCheckingTest
+)
+
 add_libc_test(
   wctob_test
   SUITE
diff --git a/libc/test/src/wchar/mblen_test.cpp b/libc/test/src/wchar/mblen_test.cpp
new file mode 100644
index 0000000000000..f7a9dc55bdab6
--- /dev/null
+++ b/libc/test/src/wchar/mblen_test.cpp
@@ -0,0 +1,105 @@
+//===-- Unittests for mblen -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/types/wchar_t.h"
+#include "src/__support/libc_errno.h"
+#include "src/wchar/mblen.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcMBLenTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcMBLenTest, OneByte) {
+  const char *ch = "A";
+  int n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, 1);
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 0);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, -1);
+}
+
+TEST_F(LlvmLibcMBLenTest, TwoByte) {
+  const char ch[2] = {static_cast<char>(0xC2),
+                      static_cast<char>(0x8E)}; // Ž car symbol
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, 2);
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+  // Should fail after trying to read next byte too
+  n = LIBC_NAMESPACE::mblen(ch + 1, 1);
+  ASSERT_EQ(n, -1);
+  // This one should be an invalid starting byte so should set errno
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBLenTest, ThreeByte) {
+  const char ch[3] = {static_cast<char>(0xE2), static_cast<char>(0x88),
+                      static_cast<char>(0x91)}; // ∑ sigma symbol
+  int n = LIBC_NAMESPACE::mblen(ch, 3);
+  ASSERT_EQ(n, 3);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 2);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, FourByte) {
+  const char ch[4] = {static_cast<char>(0xF0), static_cast<char>(0x9F),
+                      static_cast<char>(0xA4),
+                      static_cast<char>(0xA1)}; // 🤡 clown emoji
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_EQ(n, 4);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 2);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, InvalidByte) {
+  const char ch[1] = {static_cast<char>(0x80)};
+  int n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBLenTest, InvalidMultiByte) {
+  const char ch[4] = {static_cast<char>(0x80), static_cast<char>(0x00),
+                      static_cast<char>(0x80),
+                      static_cast<char>(0x00)}; // invalid sequence of bytes
+  // Trying to push all 4 should error
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+
+  // Trying to push the second and third should correspond to null wc
+  n = LIBC_NAMESPACE::mblen(ch + 1, 2);
+  ASSERT_EQ(n, 0);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, NullString) {
+  // reading on nullptr should return 0
+  int n = LIBC_NAMESPACE::mblen(nullptr, 2);
+  ASSERT_EQ(n, 0);
+  ASSERT_ERRNO_SUCCESS();
+  // reading a null terminator should return 0
+  const char *ch = "\0";
+  n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, 0);
+}

>From 692505f894ce6c631ecf69f44c40abe9829a5c15 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Tue, 22 Jul 2025 22:48:43 +0000
Subject: [PATCH 2/5] implemented mbrlen

---
 libc/config/linux/x86_64/entrypoints.txt |   1 +
 libc/include/wchar.yaml                  |   8 ++
 libc/src/wchar/CMakeLists.txt            |  17 +++-
 libc/src/wchar/mblen.cpp                 |   5 +-
 libc/src/wchar/mbrlen.cpp                |   3 +-
 libc/test/src/wchar/CMakeLists.txt       |  16 +++-
 libc/test/src/wchar/mblen_test.cpp       |   1 -
 libc/test/src/wchar/mbrlen_test.cpp      | 105 +++++++++++++++++++++++
 8 files changed, 147 insertions(+), 9 deletions(-)
 create mode 100644 libc/test/src/wchar/mbrlen_test.cpp

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 5610c946a90fb..3cb1c483cea9e 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1262,6 +1262,7 @@ if(LLVM_LIBC_FULL_BUILD)
 
     # wchar.h entrypoints
     libc.src.wchar.mblen
+    libc.src.wchar.mbrlen
     libc.src.wchar.mbrtowc
     libc.src.wchar.mbtowc
     libc.src.wchar.wcrtomb
diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 605e505dc3bc7..9b2dcf0943eed 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -60,6 +60,14 @@ functions:
     arguments:
       - type: const char *__restrict
       - type: size_t
+  - name: mbrlen
+    standards:
+      - stdc
+    return_type: size_t
+    arguments:
+      - type: const char *__restrict
+      - type: size_t
+      - type: mbstate_t *__restrict
   - name: wmemset
     standards:
       - stdc
diff --git a/libc/src/wchar/CMakeLists.txt b/libc/src/wchar/CMakeLists.txt
index 5bc294eeec587..4748177d9e6f1 100644
--- a/libc/src/wchar/CMakeLists.txt
+++ b/libc/src/wchar/CMakeLists.txt
@@ -167,7 +167,6 @@ add_entrypoint_object(
     mblen.h
   DEPENDS
     libc.hdr.types.size_t
-    libc.hdr.types.wchar_t
     libc.src.__support.common
     libc.src.__support.macros.config
     libc.src.__support.libc_errno
@@ -175,6 +174,22 @@ add_entrypoint_object(
     libc.src.__support.wchar.mbstate
 )
 
+add_entrypoint_object(
+  mbrlen
+  SRCS
+    mbrlen.cpp
+  HDRS
+    mbrlen.h
+  DEPENDS
+    libc.hdr.types.size_t
+    libc.hdr.types.mbstate_t
+    libc.src.__support.common
+    libc.src.__support.macros.config
+    libc.src.__support.wchar.mbrtowc
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbstate
+)
+
 add_entrypoint_object(
   wmemset
   SRCS
diff --git a/libc/src/wchar/mblen.cpp b/libc/src/wchar/mblen.cpp
index 0f7b94dcf7ca5..2b8f529325d25 100644
--- a/libc/src/wchar/mblen.cpp
+++ b/libc/src/wchar/mblen.cpp
@@ -9,7 +9,6 @@
 #include "src/wchar/mblen.h"
 
 #include "hdr/types/size_t.h"
-#include "hdr/types/wchar_t.h"
 #include "src/__support/common.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
@@ -23,9 +22,7 @@ LLVM_LIBC_FUNCTION(int, mblen, (const char *__restrict s, size_t n)) {
   if (s == nullptr)
     return 0;
   internal::mbstate internal_mbstate;
-  // temp ptr to use for internal function
-  wchar_t buf[1];
-  auto ret = internal::mbrtowc(buf, s, n, &internal_mbstate);
+  auto ret = internal::mbrtowc(nullptr, s, n, &internal_mbstate);
   if (!ret.has_value() || static_cast<int>(ret.value()) == -2) {
     // Encoding failure
     if (!ret.has_value())
diff --git a/libc/src/wchar/mbrlen.cpp b/libc/src/wchar/mbrlen.cpp
index 0a256f8d50102..8de78e099566b 100644
--- a/libc/src/wchar/mbrlen.cpp
+++ b/libc/src/wchar/mbrlen.cpp
@@ -10,7 +10,6 @@
 
 #include "hdr/types/mbstate_t.h"
 #include "hdr/types/size_t.h"
-#include "hdr/types/wchar_t.h"
 #include "src/__support/common.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/config.h"
@@ -23,7 +22,7 @@ LLVM_LIBC_FUNCTION(size_t, mbrlen,
                    (const char *__restrict s, size_t n,
                     mbstate_t *__restrict ps)) {
   static internal::mbstate internal_mbstate;
-  auto ret = internal::mbrtowc(pwc, s, n,
+  auto ret = internal::mbrtowc(nullptr, s, n,
                                ps == nullptr
                                    ? &internal_mbstate
                                    : reinterpret_cast<internal::mbstate *>(ps));
diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index de0cd697b3a02..5251823b44d13 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -73,7 +73,21 @@ add_libc_test(
   DEPENDS
     libc.src.__support.libc_errno
     libc.src.wchar.mblen
-    libc.hdr.types.wchar_t
+    libc.test.UnitTest.ErrnoCheckingTest
+)
+
+add_libc_test(
+  mbrtowc_test
+  SUITE
+    libc_wchar_unittests
+  SRCS
+    mbrtowc_test.cpp
+  DEPENDS
+    libc.src.__support.libc_errno
+    libc.src.__support.wchar.mbstate
+    libc.src.string.memset
+    libc.src.wchar.mbrtowc
+    libc.hdr.types.mbstate_t
     libc.test.UnitTest.ErrnoCheckingTest
 )
 
diff --git a/libc/test/src/wchar/mblen_test.cpp b/libc/test/src/wchar/mblen_test.cpp
index f7a9dc55bdab6..efd4df7020741 100644
--- a/libc/test/src/wchar/mblen_test.cpp
+++ b/libc/test/src/wchar/mblen_test.cpp
@@ -6,7 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "hdr/types/wchar_t.h"
 #include "src/__support/libc_errno.h"
 #include "src/wchar/mblen.h"
 #include "test/UnitTest/ErrnoCheckingTest.h"
diff --git a/libc/test/src/wchar/mbrlen_test.cpp b/libc/test/src/wchar/mbrlen_test.cpp
new file mode 100644
index 0000000000000..f7a9dc55bdab6
--- /dev/null
+++ b/libc/test/src/wchar/mbrlen_test.cpp
@@ -0,0 +1,105 @@
+//===-- Unittests for mblen -----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "hdr/types/wchar_t.h"
+#include "src/__support/libc_errno.h"
+#include "src/wchar/mblen.h"
+#include "test/UnitTest/ErrnoCheckingTest.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcMBLenTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+
+TEST_F(LlvmLibcMBLenTest, OneByte) {
+  const char *ch = "A";
+  int n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, 1);
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 0);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, -1);
+}
+
+TEST_F(LlvmLibcMBLenTest, TwoByte) {
+  const char ch[2] = {static_cast<char>(0xC2),
+                      static_cast<char>(0x8E)}; // Ž car symbol
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_ERRNO_SUCCESS();
+  ASSERT_EQ(n, 2);
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+  // Should fail after trying to read next byte too
+  n = LIBC_NAMESPACE::mblen(ch + 1, 1);
+  ASSERT_EQ(n, -1);
+  // This one should be an invalid starting byte so should set errno
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBLenTest, ThreeByte) {
+  const char ch[3] = {static_cast<char>(0xE2), static_cast<char>(0x88),
+                      static_cast<char>(0x91)}; // ∑ sigma symbol
+  int n = LIBC_NAMESPACE::mblen(ch, 3);
+  ASSERT_EQ(n, 3);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 2);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, FourByte) {
+  const char ch[4] = {static_cast<char>(0xF0), static_cast<char>(0x9F),
+                      static_cast<char>(0xA4),
+                      static_cast<char>(0xA1)}; // 🤡 clown emoji
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_EQ(n, 4);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mblen(ch, 2);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, InvalidByte) {
+  const char ch[1] = {static_cast<char>(0x80)};
+  int n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+}
+
+TEST_F(LlvmLibcMBLenTest, InvalidMultiByte) {
+  const char ch[4] = {static_cast<char>(0x80), static_cast<char>(0x00),
+                      static_cast<char>(0x80),
+                      static_cast<char>(0x00)}; // invalid sequence of bytes
+  // Trying to push all 4 should error
+  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  ASSERT_EQ(n, -1);
+  ASSERT_ERRNO_EQ(EILSEQ);
+
+  // Trying to push the second and third should correspond to null wc
+  n = LIBC_NAMESPACE::mblen(ch + 1, 2);
+  ASSERT_EQ(n, 0);
+  ASSERT_ERRNO_SUCCESS();
+}
+
+TEST_F(LlvmLibcMBLenTest, NullString) {
+  // reading on nullptr should return 0
+  int n = LIBC_NAMESPACE::mblen(nullptr, 2);
+  ASSERT_EQ(n, 0);
+  ASSERT_ERRNO_SUCCESS();
+  // reading a null terminator should return 0
+  const char *ch = "\0";
+  n = LIBC_NAMESPACE::mblen(ch, 1);
+  ASSERT_EQ(n, 0);
+}

>From 1eab8def2725d32b7a67e40fedb8bcdbef7058b4 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Tue, 22 Jul 2025 23:18:42 +0000
Subject: [PATCH 3/5] [libc] Implemented mblen functions

Implemented mblen and mbrlen as well as tests
---
 libc/test/src/wchar/CMakeLists.txt  |   6 +-
 libc/test/src/wchar/mbrlen_test.cpp | 116 ++++++++++++++++++----------
 2 files changed, 78 insertions(+), 44 deletions(-)

diff --git a/libc/test/src/wchar/CMakeLists.txt b/libc/test/src/wchar/CMakeLists.txt
index 5251823b44d13..baa52b74c3d97 100644
--- a/libc/test/src/wchar/CMakeLists.txt
+++ b/libc/test/src/wchar/CMakeLists.txt
@@ -77,16 +77,16 @@ add_libc_test(
 )
 
 add_libc_test(
-  mbrtowc_test
+  mbrlen_test
   SUITE
     libc_wchar_unittests
   SRCS
-    mbrtowc_test.cpp
+    mbrlen_test.cpp
   DEPENDS
     libc.src.__support.libc_errno
     libc.src.__support.wchar.mbstate
     libc.src.string.memset
-    libc.src.wchar.mbrtowc
+    libc.src.wchar.mbrlen
     libc.hdr.types.mbstate_t
     libc.test.UnitTest.ErrnoCheckingTest
 )
diff --git a/libc/test/src/wchar/mbrlen_test.cpp b/libc/test/src/wchar/mbrlen_test.cpp
index f7a9dc55bdab6..e1452bf416054 100644
--- a/libc/test/src/wchar/mbrlen_test.cpp
+++ b/libc/test/src/wchar/mbrlen_test.cpp
@@ -1,4 +1,4 @@
-//===-- Unittests for mblen -----------------------------------------------===//
+//===-- Unittests for mbrlen ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -8,98 +8,132 @@
 
 #include "hdr/types/wchar_t.h"
 #include "src/__support/libc_errno.h"
-#include "src/wchar/mblen.h"
+#include "src/__support/wchar/mbstate.h"
+#include "src/string/memset.h"
+#include "src/wchar/mbrlen.h"
 #include "test/UnitTest/ErrnoCheckingTest.h"
 #include "test/UnitTest/Test.h"
 
-using LlvmLibcMBLenTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
+using LlvmLibcMBRLenTest = LIBC_NAMESPACE::testing::ErrnoCheckingTest;
 
-TEST_F(LlvmLibcMBLenTest, OneByte) {
+TEST_F(LlvmLibcMBRLenTest, OneByte) {
   const char *ch = "A";
-  int n = LIBC_NAMESPACE::mblen(ch, 1);
+  mbstate_t mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 1, &mb);
   ASSERT_ERRNO_SUCCESS();
-  ASSERT_EQ(n, 1);
+  ASSERT_EQ(n, static_cast<size_t>(1));
 
   // Should fail since we have not read enough
-  n = LIBC_NAMESPACE::mblen(ch, 0);
+  n = LIBC_NAMESPACE::mbrlen(ch, 0, &mb);
   ASSERT_ERRNO_SUCCESS();
-  ASSERT_EQ(n, -1);
+  ASSERT_EQ(n, static_cast<size_t>(-2));
 }
 
-TEST_F(LlvmLibcMBLenTest, TwoByte) {
+TEST_F(LlvmLibcMBRLenTest, TwoByte) {
   const char ch[2] = {static_cast<char>(0xC2),
                       static_cast<char>(0x8E)}; // Ž car symbol
-  int n = LIBC_NAMESPACE::mblen(ch, 4);
+  mbstate_t mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 4, nullptr);
   ASSERT_ERRNO_SUCCESS();
-  ASSERT_EQ(n, 2);
+  ASSERT_EQ(static_cast<int>(n), 2);
 
   // Should fail since we have not read enough
-  n = LIBC_NAMESPACE::mblen(ch, 1);
-  ASSERT_EQ(n, -1);
+  n = LIBC_NAMESPACE::mbrlen(ch, 1, &mb);
+  ASSERT_EQ(static_cast<int>(n), -2);
+  ASSERT_ERRNO_SUCCESS();
+  // Should pass after trying to read next byte
+  n = LIBC_NAMESPACE::mbrlen(ch + 1, 1, &mb);
+  ASSERT_EQ(static_cast<int>(n), 1);
   ASSERT_ERRNO_SUCCESS();
-  // Should fail after trying to read next byte too
-  n = LIBC_NAMESPACE::mblen(ch + 1, 1);
-  ASSERT_EQ(n, -1);
-  // This one should be an invalid starting byte so should set errno
-  ASSERT_ERRNO_EQ(EILSEQ);
 }
 
-TEST_F(LlvmLibcMBLenTest, ThreeByte) {
+TEST_F(LlvmLibcMBRLenTest, ThreeByte) {
   const char ch[3] = {static_cast<char>(0xE2), static_cast<char>(0x88),
                       static_cast<char>(0x91)}; // ∑ sigma symbol
-  int n = LIBC_NAMESPACE::mblen(ch, 3);
-  ASSERT_EQ(n, 3);
+  mbstate_t mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 3, &mb);
+  ASSERT_EQ(static_cast<int>(n), 3);
   ASSERT_ERRNO_SUCCESS();
 
   // Should fail since we have not read enough
-  n = LIBC_NAMESPACE::mblen(ch, 2);
-  ASSERT_EQ(n, -1);
+  n = LIBC_NAMESPACE::mbrlen(ch, 2, &mb);
+  ASSERT_EQ(static_cast<int>(n), -2);
   ASSERT_ERRNO_SUCCESS();
 }
 
-TEST_F(LlvmLibcMBLenTest, FourByte) {
+TEST_F(LlvmLibcMBRLenTest, FourByte) {
   const char ch[4] = {static_cast<char>(0xF0), static_cast<char>(0x9F),
                       static_cast<char>(0xA4),
                       static_cast<char>(0xA1)}; // 🤡 clown emoji
-  int n = LIBC_NAMESPACE::mblen(ch, 4);
-  ASSERT_EQ(n, 4);
+  mbstate_t mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 4, &mb);
+  ASSERT_EQ(static_cast<int>(n), 4);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should fail since we have not read enough
+  n = LIBC_NAMESPACE::mbrlen(ch, 2, &mb);
+  ASSERT_EQ(static_cast<int>(n), -2);
   ASSERT_ERRNO_SUCCESS();
 
   // Should fail since we have not read enough
-  n = LIBC_NAMESPACE::mblen(ch, 2);
-  ASSERT_EQ(n, -1);
+  n = LIBC_NAMESPACE::mbrlen(ch + 2, 1, &mb);
+  ASSERT_EQ(static_cast<int>(n), -2);
+  ASSERT_ERRNO_SUCCESS();
+
+  // Should pass after reading final byte
+  n = LIBC_NAMESPACE::mbrlen(ch + 3, 5, &mb);
+  ASSERT_EQ(static_cast<int>(n), 1);
   ASSERT_ERRNO_SUCCESS();
 }
 
-TEST_F(LlvmLibcMBLenTest, InvalidByte) {
+TEST_F(LlvmLibcMBRLenTest, InvalidByte) {
   const char ch[1] = {static_cast<char>(0x80)};
-  int n = LIBC_NAMESPACE::mblen(ch, 1);
-  ASSERT_EQ(n, -1);
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 1, nullptr);
+  ASSERT_EQ(static_cast<int>(n), -1);
   ASSERT_ERRNO_EQ(EILSEQ);
 }
 
-TEST_F(LlvmLibcMBLenTest, InvalidMultiByte) {
+TEST_F(LlvmLibcMBRLenTest, InvalidMultiByte) {
   const char ch[4] = {static_cast<char>(0x80), static_cast<char>(0x00),
                       static_cast<char>(0x80),
                       static_cast<char>(0x00)}; // invalid sequence of bytes
+  mbstate_t mb;
+  LIBC_NAMESPACE::memset(&mb, 0, sizeof(mbstate_t));
   // Trying to push all 4 should error
-  int n = LIBC_NAMESPACE::mblen(ch, 4);
-  ASSERT_EQ(n, -1);
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 4, &mb);
+  ASSERT_EQ(static_cast<int>(n), -1);
   ASSERT_ERRNO_EQ(EILSEQ);
 
   // Trying to push the second and third should correspond to null wc
-  n = LIBC_NAMESPACE::mblen(ch + 1, 2);
-  ASSERT_EQ(n, 0);
+  n = LIBC_NAMESPACE::mbrlen(ch + 1, 2, &mb);
+  ASSERT_EQ(static_cast<int>(n), 0);
   ASSERT_ERRNO_SUCCESS();
 }
 
-TEST_F(LlvmLibcMBLenTest, NullString) {
+TEST_F(LlvmLibcMBRLenTest, NullString) {
   // reading on nullptr should return 0
-  int n = LIBC_NAMESPACE::mblen(nullptr, 2);
-  ASSERT_EQ(n, 0);
+  size_t n = LIBC_NAMESPACE::mbrlen(nullptr, 2, nullptr);
+  ASSERT_EQ(static_cast<int>(n), 0);
   ASSERT_ERRNO_SUCCESS();
   // reading a null terminator should return 0
   const char *ch = "\0";
-  n = LIBC_NAMESPACE::mblen(ch, 1);
-  ASSERT_EQ(n, 0);
+  n = LIBC_NAMESPACE::mbrlen(ch, 1, nullptr);
+  ASSERT_EQ(static_cast<int>(n), 0);
+}
+
+TEST_F(LlvmLibcMBRLenTest, InvalidMBState) {
+  const char ch[4] = {static_cast<char>(0xC2), static_cast<char>(0x8E),
+                      static_cast<char>(0xC7), static_cast<char>(0x8C)};
+  mbstate_t *mb;
+  LIBC_NAMESPACE::internal::mbstate inv;
+  inv.total_bytes = 6;
+  mb = reinterpret_cast<mbstate_t *>(&inv);
+  // invalid mbstate should error
+  size_t n = LIBC_NAMESPACE::mbrlen(ch, 2, mb);
+  ASSERT_EQ(static_cast<int>(n), -1);
+  ASSERT_ERRNO_EQ(EINVAL);
 }

>From 4c591a2f664a15c370e5cbc662eb3d156ec7f580 Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Thu, 24 Jul 2025 17:09:47 +0000
Subject: [PATCH 4/5] removed restrict from parameter

---
 libc/include/wchar.yaml  | 2 +-
 libc/src/wchar/mblen.cpp | 2 +-
 libc/src/wchar/mblen.h   | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/libc/include/wchar.yaml b/libc/include/wchar.yaml
index 9b2dcf0943eed..4adf596abe650 100644
--- a/libc/include/wchar.yaml
+++ b/libc/include/wchar.yaml
@@ -58,7 +58,7 @@ functions:
       - stdc
     return_type: int
     arguments:
-      - type: const char *__restrict
+      - type: const char *
       - type: size_t
   - name: mbrlen
     standards:
diff --git a/libc/src/wchar/mblen.cpp b/libc/src/wchar/mblen.cpp
index 2b8f529325d25..d6694a6558dc6 100644
--- a/libc/src/wchar/mblen.cpp
+++ b/libc/src/wchar/mblen.cpp
@@ -17,7 +17,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
-LLVM_LIBC_FUNCTION(int, mblen, (const char *__restrict s, size_t n)) {
+LLVM_LIBC_FUNCTION(int, mblen, (const char * s, size_t n)) {
   // returns 0 since UTF-8 encoding is not state-dependent
   if (s == nullptr)
     return 0;
diff --git a/libc/src/wchar/mblen.h b/libc/src/wchar/mblen.h
index 982081270cf9a..03f158711250a 100644
--- a/libc/src/wchar/mblen.h
+++ b/libc/src/wchar/mblen.h
@@ -14,7 +14,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
-int mblen(const char *__restrict s, size_t n);
+int mblen(const char * s, size_t n);
 
 } // namespace LIBC_NAMESPACE_DECL
 

>From e52ee8956616fb22f332ea95fb40c4ffe4548a1b Mon Sep 17 00:00:00 2001
From: Sriya Pratipati <sriyap at google.com>
Date: Thu, 24 Jul 2025 17:16:24 +0000
Subject: [PATCH 5/5] fixed formatting

---
 libc/src/wchar/mblen.cpp | 2 +-
 libc/src/wchar/mblen.h   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libc/src/wchar/mblen.cpp b/libc/src/wchar/mblen.cpp
index d6694a6558dc6..2d15b3e0e5648 100644
--- a/libc/src/wchar/mblen.cpp
+++ b/libc/src/wchar/mblen.cpp
@@ -17,7 +17,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
-LLVM_LIBC_FUNCTION(int, mblen, (const char * s, size_t n)) {
+LLVM_LIBC_FUNCTION(int, mblen, (const char *s, size_t n)) {
   // returns 0 since UTF-8 encoding is not state-dependent
   if (s == nullptr)
     return 0;
diff --git a/libc/src/wchar/mblen.h b/libc/src/wchar/mblen.h
index 03f158711250a..a315a2f12f6a1 100644
--- a/libc/src/wchar/mblen.h
+++ b/libc/src/wchar/mblen.h
@@ -14,7 +14,7 @@
 
 namespace LIBC_NAMESPACE_DECL {
 
-int mblen(const char * s, size_t n);
+int mblen(const char *s, size_t n);
 
 } // namespace LIBC_NAMESPACE_DECL

More information about the libc-commits mailing list