universal internal strlen for all char types

ostd/string.hh

@@ -73,6 +73,13 @@ static_assert(
     "wchar_t must correspond to either char, char16_t or char32_t"
 );
 
+namespace detail {
+    std::size_t tstrlen(char const *p) noexcept;
+    std::size_t tstrlen(char16_t const *p) noexcept;
+    std::size_t tstrlen(char32_t const *p) noexcept;
+    std::size_t tstrlen(wchar_t const *p) noexcept;
+}
+
 /** @addtogroup Strings
  * @{
  */
@@ -135,7 +142,7 @@ public:
             std::size_t N = std::extent_v<std::remove_reference_t<U>>;
             p_end = beg + N - (beg[N - 1] == '\0');
         } else {
-            p_end = beg + (beg ? std::strlen(beg) : 0);
+            p_end = beg + (beg ? detail::tstrlen(beg) : 0);
         }
     }
 
@@ -181,7 +188,7 @@ public:
      * The data pointed to by the argument must be zero terminated.
      */
     basic_char_range &operator=(value_type *s) noexcept {
-        p_beg = s; p_end = s + (s ? std::strlen(s) : 0); return *this;
+        p_beg = s; p_end = s + (s ? detail::tstrlen(s) : 0); return *this;
     }
 
     /** @brief Checks if the slice is empty. */

src/string.cc

@@ -5,9 +5,57 @@
 
 #include <cstdint>
 #include <cstdlib>
+#include <cstring>
+#include <limits>
+#include <type_traits>
 #include "ostd/string.hh"
 #include "ostd/format.hh"
 
+namespace ostd {
+namespace detail {
+
+template<typename C>
+inline std::size_t tstrlen_impl(C const *p) noexcept {
+    using SL = std::numeric_limits<std::size_t>;
+    using UL = std::numeric_limits<std::make_unsigned_t<C>>;
+    constexpr std::size_t Lbits = SL::max() / UL::max();
+    constexpr std::size_t Hbits = Lbits << (UL::digits - 1);
+
+    C const *bp = p;
+    if constexpr(sizeof(C) >= sizeof(std::size_t)) {
+        goto sloop;
+    }
+    for (; std::uintptr_t(p) % sizeof(std::size_t); ++p) {
+        if (!*p) {
+            return (p - bp);
+        }
+    }
+    {
+        auto *wp = reinterpret_cast<std::size_t const *>(p);
+        for (; !(((*wp - Lbits) & ~*wp) & Hbits); ++wp) {}
+        p = reinterpret_cast<C const *>(wp);
+    }
+sloop:
+    for (; *p; ++p) {}
+    return (p - bp);
+}
+
+std::size_t tstrlen(char const *p) noexcept {
+    return tstrlen_impl(p);
+}
+std::size_t tstrlen(char16_t const *p) noexcept {
+    return tstrlen_impl(p);
+}
+std::size_t tstrlen(char32_t const *p) noexcept {
+    return tstrlen_impl(p);
+}
+std::size_t tstrlen(wchar_t const *p) noexcept {
+    return tstrlen_impl(p);
+}
+
+} /* namespace detail */
+} /* namespace ostd */
+
 namespace ostd {
 namespace utf {