Export of internal Abseil changes

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a9ac6567c0933d786d68c10011e3f3ff9deedf89 by Greg Falcon <gfalcon@google.com>:

Add absl::FunctionRef, a type analogous to the proposed C++23 std::function_ref.

Like std::function, FunctionRef can be used to type-erase any callable (invokable) object.  However, FunctionRef works by reference: it does not store a copy of the type-erased object.  If the wrapped object is destroyed before the FunctionRef, the reference becomes dangling.

FunctionRef relates to std::function in much the same way that string_view relates to std::string.

Because of these limitations, FunctionRef is best used only as a function argument type, and only where the function will be invoked immediately (rather than saved for later use).  When `const std::function<...>&` is used in this way, `absl::FunctionRef<...>` is a better-performing replacement.

PiperOrigin-RevId: 275484044

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1f7c4df3760f8b93e5a5baf40b070eca1d3f4c98 by Abseil Team <absl-team@google.com>:

Add FastHexToBufferZeroPad16() function for blazingly fast hex encoding of uint64_t.

PiperOrigin-RevId: 275420901

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08d48ac004eba57cf2f1ada827181a2995f74807 by Abseil Team <absl-team@google.com>:

Avoid applying the workaround for MSVC's static initialization problems when using clang-cl.

PiperOrigin-RevId: 275366326

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40be82bd2b34670b5458c0a72a0475086153c2d6 by Abseil Team <absl-team@google.com>:

Added comments to SimpleAtof()/SimpleAtod() that clarify that they
always use the "C" locale, unlike the standard functions strtod()
and strtof() referenced now in the comments.

PiperOrigin-RevId: 275355815

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086779dacb3f6f2b3ab59947e94e79046bdb1fe1 by Jorg Brown <jorg@google.com>:

Move the hex conversion table used by escaping.cc into numbers.h so
that other parts of Abseil can more efficiently access it.

PiperOrigin-RevId: 275331251

--
3c4ed1b04e55d96a40cbe70fb70929ffbb0c0432 by Abseil Team <absl-team@google.com>:

Avoid applying the workaround for MSVC's static initialization problems when using clang-cl.

PiperOrigin-RevId: 275323858

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56ceb58ab688c3761978308609b09a1ac2739c9a by Derek Mauro <dmauro@google.com>:

Add script for testing on Alpine Linux (for musl test coverage)

PiperOrigin-RevId: 275321244
GitOrigin-RevId: a9ac6567c0933d786d68c10011e3f3ff9deedf89
Change-Id: I39799fa03768ddb44f3166200c860e1da4461807

1 files changed, 43 insertions, 2 deletions

diff --git a/absl/strings/numbers.h b/absl/strings/numbers.h
index 100839b04626..745de67ad86d 100644
--- a/absl/strings/numbers.h
+++ b/absl/strings/numbers.h
@@ -24,6 +24,10 @@
 #ifndef ABSL_STRINGS_NUMBERS_H_
 #define ABSL_STRINGS_NUMBERS_H_
 
+#ifdef __SSE4_2__
+#include <x86intrin.h>
+#endif
+
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
@@ -32,6 +36,8 @@
 #include <string>
 #include <type_traits>
 
+#include "absl/base/internal/bits.h"
+#include "absl/base/internal/endian.h"
 #include "absl/base/macros.h"
 #include "absl/base/port.h"
 #include "absl/numeric/int128.h"
@@ -54,7 +60,8 @@ ABSL_MUST_USE_RESULT bool SimpleAtoi(absl::string_view str, int_type* out);
 // Converts the given string (optionally followed or preceded by ASCII
 // whitespace) into a float, which may be rounded on overflow or underflow.
 // See https://en.cppreference.com/w/c/string/byte/strtof for details about the
-// allowed formats for `str`. If any errors are encountered, this function
+// allowed formats for `str`, except SimpleAtof() is locale-indepdent and will
+// always use the "C" locale. If any errors are encountered, this function
 // returns `false`, leaving `out` in an unspecified state.
 ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str, float* out);
 
@@ -63,7 +70,8 @@ ABSL_MUST_USE_RESULT bool SimpleAtof(absl::string_view str, float* out);
 // Converts the given string (optionally followed or preceded by ASCII
 // whitespace) into a double, which may be rounded on overflow or underflow.
 // See https://en.cppreference.com/w/c/string/byte/strtof for details about the
-// allowed formats for `str`. If any errors are encountered, this function
+// allowed formats for `str`, except SimpleAtod is locale-independent and will
+// always use the "C" locale. If any errors are encountered, this function
 // returns `false`, leaving `out` in an unspecified state.
 ABSL_MUST_USE_RESULT bool SimpleAtod(absl::string_view str, double* out);
 
@@ -84,6 +92,10 @@ ABSL_MUST_USE_RESULT bool SimpleAtob(absl::string_view str, bool* out);
 namespace absl {
 namespace numbers_internal {
 
+// Digit conversion.
+extern const char kHexChar[17];    // 0123456789abcdef
+extern const char kHexTable[513];  // 000102030405060708090a0b0c0d0e0f1011...
+
 // safe_strto?() functions for implementing SimpleAtoi()
 bool safe_strto32_base(absl::string_view text, int32_t* value, int base);
 bool safe_strto64_base(absl::string_view text, int64_t* value, int base);
@@ -170,6 +182,35 @@ ABSL_MUST_USE_RESULT bool safe_strtoi_base(absl::string_view s, int_type* out,
   return parsed;
 }
 
+// FastHexToBufferZeroPad16()
+//
+// Outputs `val` into `out` as if by `snprintf(out, 17, "%016x", val)` but
+// without the terminating null character. Thus `out` must be of length >= 16.
+// Returns the number of non-pad digits of the output (it can never be zero
+// since 0 has one digit).
+inline size_t FastHexToBufferZeroPad16(uint64_t val, char* out) {
+  uint64_t be = absl::big_endian::FromHost64(val);
+#ifdef __SSE4_2__
+  const auto kNibbleMask = _mm_set1_epi8(0xf);
+  const auto kHexDigits = _mm_setr_epi8('0', '1', '2', '3', '4', '5', '6', '7',
+                                        '8', '9', 'a', 'b', 'c', 'd', 'e', 'f');
+  auto v = _mm_loadu_si64(reinterpret_cast<__m128i*>(&be));  // load lo dword
+  auto v4 = _mm_srli_epi64(v, 4);                            // shift 4 right
+  auto il = _mm_unpacklo_epi8(v4, v);                        // interleave bytes
+  auto m = _mm_and_si128(il, kNibbleMask);                   // mask out nibbles
+  auto hexchars = _mm_shuffle_epi8(kHexDigits, m);           // hex chars
+  _mm_storeu_si128(reinterpret_cast<__m128i*>(out), hexchars);
+#else
+  for (int i = 0; i < 8; ++i) {
+    auto byte = (be >> (8 * i)) & 0xFF;
+    auto* hex = &absl::numbers_internal::kHexTable[byte * 2];
+    std::memcpy(out + 2 * i, hex, 2);
+  }
+#endif
+  // | 0x1 so that even 0 has 1 digit.
+  return 16 - absl::base_internal::CountLeadingZeros64(val | 0x1) / 4;
+}
+
 }  // namespace numbers_internal
 
 // SimpleAtoi()