QByteArrayView: inline the char overload of lastIndexOf()

It's just memrchr()... which unfortunately is a GNU extension (picked by
FreeBSD and OpenBSD too), so we need to provide a fallback
implementation for other OSes and bootstrap mode.

By creating a new overload instead of doing the inlining trick, this
gets inlined in QtCore uses as well and has a simpler #ifdef'ery. We
still reach the C library function indirectly, but that's going to be
minimal (and unavoidable) overhead, more than offset by the gain in
accessing an optimized memrchr().

Change-Id: If05cb740b64f42eba21efffd17d0b681bcfe9cf3
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/compat/removed_api.cpp

@@ -954,6 +954,15 @@ bool QPersistentModelIndex::operator!=(const QModelIndex &other) const noexcept
 
 #include "qbytearray.h" // inlined API
 
+QT_BEGIN_NAMESPACE
+namespace QtPrivate {
+Q_CORE_EXPORT qsizetype lastIndexOf(QByteArrayView haystack, qsizetype from, char needle) noexcept
+{
+    return lastIndexOf(haystack, from, uchar(needle));
+}
+}
+QT_END_NAMESPACE
+
 #include "qcborarray.h" // inlined API
 
 #include "qcbormap.h" // inlined API

src/corelib/configure.cmake

@@ -324,6 +324,21 @@ linkat(AT_FDCWD, \"foo\", AT_FDCWD, \"bar\", AT_SYMLINK_FOLLOW);
 }
 ")
 
+# memrchr
+qt_config_compile_test(memrchr
+    LABEL "memrchr()"
+    CODE
+"#define _BSD_SOURCE 1   /* For FreeBSD */
+#define _GNU_SOURCE 1   /* For glibc, Bionic */
+#include <string.h>
+
+int main(void)
+{
+    const void *r = memrchr(\"abc\", 'a', 3);
+    (void)r;
+    return 0;
+}")
+
 # ppoll
 qt_config_compile_test(ppoll
     LABEL "ppoll()"
@@ -554,6 +569,10 @@ qt_feature("std-atomic64" PUBLIC
     LABEL "64 bit atomic operations"
     CONDITION WrapAtomic_FOUND
 )
+qt_feature("memrchr" PRIVATE
+    LABEL "C library function memrchr()"
+    CONDITION TEST_memrchr
+)
 qt_feature("mimetype" PUBLIC
     SECTION "Utilities"
     LABEL "Mimetype handling"

src/corelib/global/qconfig-bootstrapped.h

@@ -72,6 +72,7 @@
 # define QT_FEATURE_linkat -1
 #endif
 #define QT_FEATURE_lttng -1
+#define QT_FEATURE_memrchr -1
 #define QT_NO_QOBJECT
 #define QT_FEATURE_process -1
 #define QT_FEATURE_regularexpression 1

src/corelib/text/qbytearray.cpp

@@ -60,6 +60,30 @@ static constexpr inline uchar asciiLower(uchar c)
   Safe and portable C string functions; extensions to standard string.h
  *****************************************************************************/
 
+/*! \relates QByteArray
+    \internal
+
+    Wrapper around memrchr() for systems that don't have it. It's provided in
+    every system because, as a GNU extension, memrchr() may not be declared in
+    string.h depending on how strict the compiler was asked to be.
+
+    Used in QByteArrayView::lastIndexOf() overload for a single char.
+*/
+const void *qmemrchr(const void *s, int needle, size_t size) noexcept
+{
+#if QT_CONFIG(memrchr)
+    return memrchr(s, needle, size);
+#endif
+    auto b = static_cast<const char *>(s);
+    const char *n = b + size;
+    while (n-- != b) {
+        if (*n == needle)
+            return n;
+    }
+    return nullptr;
+}
+
+
 /*! \relates QByteArray
 
     Returns a duplicate string.
@@ -2738,30 +2762,6 @@ static qsizetype lastIndexOfHelper(const char *haystack, qsizetype l, const char
     return -1;
 }
 
-static inline qsizetype lastIndexOfCharHelper(QByteArrayView haystack, qsizetype from, char needle) noexcept
-{
-    if (haystack.size() == 0)
-        return -1;
-    if (from < 0)
-        from += haystack.size();
-    else if (from > haystack.size())
-        from = haystack.size() - 1;
-    if (from >= 0) {
-        const char *b = haystack.data();
-        const char *n = b + from + 1;
-        while (n-- != b) {
-            if (*n == needle)
-                return n - b;
-        }
-    }
-    return -1;
-}
-
-qsizetype QtPrivate::lastIndexOf(QByteArrayView haystack, qsizetype from, char needle) noexcept
-{
-    return lastIndexOfCharHelper(haystack, from, needle);
-}
-
 qsizetype QtPrivate::lastIndexOf(QByteArrayView haystack, qsizetype from, QByteArrayView needle) noexcept
 {
     if (haystack.isEmpty()) {
@@ -2771,7 +2771,7 @@ qsizetype QtPrivate::lastIndexOf(QByteArrayView haystack, qsizetype from, QByteA
     }
     const auto ol = needle.size();
     if (ol == 1)
-        return lastIndexOfCharHelper(haystack, from, needle.front());
+        return QtPrivate::lastIndexOf(haystack, from, needle.front());
 
     return lastIndexOfHelper(haystack.data(), haystack.size(), needle.data(), ol, from);
 }

src/corelib/text/qbytearrayalgorithms.h

@@ -31,8 +31,8 @@ qsizetype findByteArray(QByteArrayView haystack, qsizetype from, char needle) no
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION
 qsizetype findByteArray(QByteArrayView haystack, qsizetype from, QByteArrayView needle) noexcept;
 
-[[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION
-qsizetype lastIndexOf(QByteArrayView haystack, qsizetype from, char needle) noexcept;
+[[nodiscard]] inline Q_DECL_PURE_FUNCTION
+qsizetype lastIndexOf(QByteArrayView haystack, qsizetype from, uchar needle) noexcept;
 
 [[nodiscard]] Q_CORE_EXPORT Q_DECL_PURE_FUNCTION
 qsizetype lastIndexOf(QByteArrayView haystack, qsizetype from, QByteArrayView needle) noexcept;
@@ -99,6 +99,8 @@ static inline T toIntegral(ByteArrayView data, bool *ok, int base)
   Safe and portable C string functions; extensions to standard string.h
  *****************************************************************************/
 
+[[nodiscard]] Q_DECL_PURE_FUNCTION Q_CORE_EXPORT
+const void *qmemrchr(const void *s, int needle, size_t n) noexcept;
 Q_CORE_EXPORT char *qstrdup(const char *);
 
 inline size_t qstrlen(const char *str)

src/corelib/text/qbytearrayview.h

@@ -401,6 +401,18 @@ qsizetype QtPrivate::findByteArray(QByteArrayView haystack, qsizetype from, char
     return -1;
 }
 
+qsizetype QtPrivate::lastIndexOf(QByteArrayView haystack, qsizetype from, uchar needle) noexcept
+{
+    if (from < 0)
+        from = qMax(from + haystack.size(), qsizetype(0));
+    else
+        from = qMin(from, haystack.size() - 1);
+
+    const char *const b = haystack.data();
+    const void *n = b ? qmemrchr(b, needle, from + 1) : nullptr;
+    return n ? static_cast<const char *>(n) - b : -1;
+}
+
 QT_END_NAMESPACE
 
 #endif // QBYTEARRAYVIEW_H