vector_algorithms.cpp: fix incorrect activation of bitmap find-meow-of algorithms (#5758)

Co-authored-by: Stephan T. Lavavej <stl@microsoft.com>

Author: AlexGuteniev

stl/src/vector_algorithms.cpp

@@ -3991,16 +3991,20 @@ namespace {
 
                     const size_t _Byte_size = _Needle_length * sizeof(_Ty);
 
+                    constexpr size_t _Vec_size = sizeof(_Mask);
+                    constexpr size_t _Vec_mask = _Vec_size - 1;
+                    static_assert((_Vec_size & _Vec_mask) == 0);
+
                     const void* _Stop = _Needle_ptr;
-                    _Advance_bytes(_Stop, _Byte_size & ~size_t{0x1F});
-                    for (; _Needle_ptr != _Stop; _Needle_ptr += 32 / sizeof(_Ty)) {
+                    _Advance_bytes(_Stop, _Byte_size & ~_Vec_mask);
+                    for (; _Needle_ptr != _Stop; _Needle_ptr += _Vec_size / sizeof(_Ty)) {
                         const __m128i _Data = _mm_loadu_si128(reinterpret_cast<const __m128i*>(_Needle_ptr));
                         if (!_mm_testz_si128(_Mask, _Data)) {
                             return false;
                         }
                     }
 
-                    _Advance_bytes(_Stop, _Byte_size & 0x1E);
+                    _Advance_bytes(_Stop, _Byte_size & _Vec_mask);
                     for (; _Needle_ptr != _Stop; ++_Needle_ptr) {
                         if ((*_Needle_ptr & ~_Ty{0xFF}) != 0) {
                             return false;

tests/std/tests/VSO_0000000_vector_algorithms/test.cpp

@@ -1710,6 +1710,26 @@ void test_basic_string(mt19937_64& gen) {
     }
 }
 
+// GH-5757 <string>: wstring::find_first_of crashes on some inputs
+void test_gh_5757_find_first_of() {
+    const wstring hay(40, L'e');
+    wstring needle;
+    needle.resize(32);
+
+    for (unsigned int k = 0; k != 32; k += 16) {
+        for (unsigned int i = 0; i != 8; ++i) {
+            needle[i + k] = static_cast<wchar_t>(L'a' + i);
+        }
+
+        for (unsigned int i = 8; i != 16; ++i) {
+            needle[i + k] = static_cast<wchar_t>(0xFF00 + i);
+        }
+    }
+
+    const auto pos = hay.find_first_of(needle);
+    assert(pos == 0);
+}
+
 void test_string(mt19937_64& gen) {
     test_basic_string<char>(gen);
     test_basic_string<wchar_t>(gen);
@@ -1719,6 +1739,8 @@ void test_string(mt19937_64& gen) {
     test_basic_string<char16_t>(gen);
     test_basic_string<char32_t>(gen);
     test_basic_string<unsigned long long>(gen);
+
+    test_gh_5757_find_first_of();
 }
 
 void test_various_containers() {