feat(libc): implement memrchr

core/libs/prx/libc/CMakeLists.txt

@@ -187,6 +187,15 @@ if(BUILD_TESTING)
         set_tests_properties(guest_environment PROPERTIES ENVIRONMENT_MODIFICATION
             "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
     endif()
+    add_test_executable(guest_memrchr_tests ${LIBS_INCLUDE_DIR}/tests/GuestMemrchr.cpp)
+    target_include_directories(guest_memrchr_tests PRIVATE ${LIBS_INCLUDE_DIR})
+    target_link_libraries(guest_memrchr_tests PRIVATE libc)
+    configure_windows_unwind(guest_memrchr_tests)
+    add_test(NAME guest_memrchr COMMAND guest_memrchr_tests)
+    if(WIN32)
+        set_tests_properties(guest_memrchr PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libc>")
+    endif()
     add_test_executable(guest_lifecycle_tests ${LIBS_INCLUDE_DIR}/tests/GuestLifecycle.cpp)
     target_include_directories(guest_lifecycle_tests PRIVATE ${LIBS_INCLUDE_DIR})
     target_link_libraries(guest_lifecycle_tests PRIVATE libc)

core/libs/prx/libc/src/Strings.cpp

@@ -73,6 +73,16 @@ const void* APS5_VABI memchr_nid_postfix(const void* s, int c, size_t n) {
     return std::memchr(s, c, n);
 }
 
+void* APS5_VABI memrchr_nid_postfix(const void* s, int c, size_t n) {
+    const auto* bytes = static_cast<const unsigned char*>(s);
+    const auto value = static_cast<unsigned char>(c);
+    while (n != 0) {
+        --n;
+        if (bytes[n] == value) return const_cast<unsigned char*>(bytes + n);
+    }
+    return nullptr;
+}
+
 int APS5_VABI strcmp_nid_postfix(const char* s1, const char* s2) {
     return std::strcmp(s1, s2);
 }

core/libs/tests/GuestMemrchr.cpp

@@ -0,0 +1,17 @@
+#include "prx/libc/include/general/VabiMacros.hpp"
+#include <cstdlib>
+
+extern "C" {
+void* APS5_VABI memrchr_nid_postfix(const void*, int, std::size_t);
+}
+
+int main() {
+    const unsigned char bytes[] = {0xff, 0x01, 0xff, 0x00};
+    const auto* found = static_cast<const unsigned char*>(memrchr_nid_postfix(bytes, 0xff, sizeof(bytes)));
+    if (found != bytes + 2) std::abort();
+    found = static_cast<const unsigned char*>(memrchr_nid_postfix(bytes, 0x1ff, sizeof(bytes)));
+    if (found != bytes + 2) std::abort();
+    found = static_cast<const unsigned char*>(memrchr_nid_postfix(bytes, 0xff, 2));
+    if (found != bytes) std::abort();
+    if (memrchr_nid_postfix(bytes, 0x02, sizeof(bytes)) != nullptr) std::abort();
+}