Export of internal Abseil changes

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d8ddeda8e52132b908fae89b25f117a055d78c04 by Abseil Team <absl-team@google.com>:

Improve performance of ByteStringFromAscii by changing kHexValue to have -1 in invalid value slots. This way a single load can do both the validation and conversion.

PiperOrigin-RevId: 284167344

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5037e97e2eaaac8ced9a5290949deda4b43b9ceb by Mark Barolak <mbar@google.com>:

Change the underlying symbol name of Cord to absl::Cord.

PiperOrigin-RevId: 284005429

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4ef66c72aedf135f2b4fd0ba7a73de6642decfff by Abseil Team <absl-team@google.com>:

Eliminate an unnecessary load when futex is contended in Waiter::Wait()

The first argument to compare_exchange_weak() is a reference and will be
updated upon failure.  There is no need to do an additional load on the
same variable.

PiperOrigin-RevId: 284002752
GitOrigin-RevId: d8ddeda8e52132b908fae89b25f117a055d78c04
Change-Id: Idac68a1901eb8c30050adc3860765b1a6fa085c7

absl/strings/escaping.cc

@@ -961,7 +961,7 @@ bool Base64UnescapeInternal(const char* src, size_t slen, String* dest,
 }
 
 /* clang-format off */
-constexpr char kHexValue[256] = {
+constexpr char kHexValueLenient[256] = {
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
@@ -977,8 +977,9 @@ constexpr char kHexValue[256] = {
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
     0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+    0,  0,  0,  0,  0,  0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 };
+
 /* clang-format on */
 
 // This is a templated function so that T can be either a char*
@@ -987,8 +988,8 @@ constexpr char kHexValue[256] = {
 template <typename T>
 void HexStringToBytesInternal(const char* from, T to, ptrdiff_t num) {
   for (int i = 0; i < num; i++) {
-    to[i] = (kHexValue[from[i * 2] & 0xFF] << 4) +
+    to[i] = (kHexValueLenient[from[i * 2] & 0xFF] << 4) +
-            (kHexValue[from[i * 2 + 1] & 0xFF]);
+            (kHexValueLenient[from[i * 2 + 1] & 0xFF]);
   }
 }
 

absl/strings/internal/str_format/arg.h

@@ -18,11 +18,11 @@
 #include "absl/strings/internal/str_format/extension.h"
 #include "absl/strings/string_view.h"
 
-class Cord;
 class CordReader;
 
 namespace absl {
 
+class Cord;
 class FormatCountCapture;
 class FormatSink;
 
@@ -67,7 +67,7 @@ ConvertResult<Conv::s | Conv::p> FormatConvertImpl(const char* v,
                                                    FormatSinkImpl* sink);
 template <class AbslCord,
           typename std::enable_if<
-              std::is_same<AbslCord, ::Cord>::value>::type* = nullptr,
+              std::is_same<AbslCord, absl::Cord>::value>::type* = nullptr,
           class AbslCordReader = ::CordReader>
 ConvertResult<Conv::s> FormatConvertImpl(const AbslCord& value,
                                          ConversionSpec conv,

absl/strings/internal/str_format/extension.h

@@ -25,10 +25,10 @@
 #include "absl/strings/internal/str_format/output.h"
 #include "absl/strings/string_view.h"
 
-class Cord;
-
 namespace absl {
 
+class Cord;
+
 namespace str_format_internal {
 
 class FormatRawSinkImpl {

absl/strings/internal/str_format/output.h

@@ -28,9 +28,10 @@
 #include "absl/base/port.h"
 #include "absl/strings/string_view.h"
 
+namespace absl {
+
 class Cord;
 
-namespace absl {
 namespace str_format_internal {
 
 // RawSink implementation that writes into a char* buffer.
@@ -76,7 +77,7 @@ inline void AbslFormatFlush(std::ostream* out, string_view s) {
 }
 
 template <class AbslCord, typename = typename std::enable_if<
-                              std::is_same<AbslCord, ::Cord>::value>::type>
+                              std::is_same<AbslCord, absl::Cord>::value>::type>
 inline void AbslFormatFlush(AbslCord* out, string_view s) {
   out->Append(s);
 }

absl/synchronization/internal/waiter.cc

@@ -136,7 +136,7 @@ bool Waiter::Wait(KernelTimeout t) {
   bool first_pass = true;
   while (true) {
     int32_t x = futex_.load(std::memory_order_relaxed);
-    if (x != 0) {
+    while (x != 0) {
       if (!futex_.compare_exchange_weak(x, x - 1,
                                         std::memory_order_acquire,
                                         std::memory_order_relaxed)) {
@@ -313,7 +313,7 @@ bool Waiter::Wait(KernelTimeout t) {
   bool first_pass = true;
   while (true) {
     int x = wakeups_.load(std::memory_order_relaxed);
-    if (x != 0) {
+    while (x != 0) {
       if (!wakeups_.compare_exchange_weak(x, x - 1,
                                           std::memory_order_acquire,
                                           std::memory_order_relaxed)) {