Release the CRC library

This implementation can advantage of hardware acceleration available
on common CPUs when using GCC and Clang. A future update may enable
this on MSVC as well.

PiperOrigin-RevId: 487327024
Change-Id: I99a8f1bcbdf25297e776537e23bd0a902e0818a1

1 files changed, 691 insertions, 0 deletions

diff --git a/absl/crc/internal/crc_x86_arm_combined.cc b/absl/crc/internal/crc_x86_arm_combined.cc
new file mode 100644
index 00000000..06f9c69c
--- /dev/null
+++ b/absl/crc/internal/crc_x86_arm_combined.cc
@@ -0,0 +1,691 @@
+// Copyright 2022 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Hardware accelerated CRC32 computation on Intel and ARM architecture.
+
+#include <stddef.h>
+
+#include <cstdint>
+
+#include "absl/base/attributes.h"
+#include "absl/base/call_once.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/endian.h"
+#include "absl/base/internal/prefetch.h"
+#include "absl/crc/internal/cpu_detect.h"
+#include "absl/crc/internal/crc.h"
+#include "absl/crc/internal/crc32_x86_arm_combined_simd.h"
+#include "absl/crc/internal/crc_internal.h"
+#include "absl/memory/memory.h"
+#include "absl/numeric/bits.h"
+
+#if defined(__aarch64__) && defined(__LITTLE_ENDIAN__) && \
+    defined(__ARM_FEATURE_CRC32) && defined(__ARM_NEON)
+#define ABSL_INTERNAL_CAN_USE_SIMD_CRC32C
+#elif defined(__SSE4_2__) && defined(__PCLMUL__)
+#define ABSL_INTERNAL_CAN_USE_SIMD_CRC32C
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace crc_internal {
+
+#if defined(ABSL_INTERNAL_CAN_USE_SIMD_CRC32C)
+
+// Implementation details not exported outside of file
+namespace {
+
+// Some machines have CRC acceleration hardware.
+// We can do a faster version of Extend() on such machines.
+class CRC32AcceleratedX86ARMCombined : public CRC32 {
+ public:
+  CRC32AcceleratedX86ARMCombined() {}
+  ~CRC32AcceleratedX86ARMCombined() override {}
+  void ExtendByZeroes(uint32_t* crc, size_t length) const override;
+  uint32_t ComputeZeroConstant(size_t length) const;
+
+ private:
+  CRC32AcceleratedX86ARMCombined(const CRC32AcceleratedX86ARMCombined&) =
+      delete;
+  CRC32AcceleratedX86ARMCombined& operator=(
+      const CRC32AcceleratedX86ARMCombined&) = delete;
+};
+
+// Constants for switching between algorithms.
+// Chosen by comparing speed at different powers of 2.
+constexpr int kSmallCutoff = 256;
+constexpr int kMediumCutoff = 2048;
+
+#define ABSL_INTERNAL_STEP1(crc) \
+  do {                           \
+    crc = CRC32_u8(crc, *p++);   \
+  } while (0)
+#define ABSL_INTERNAL_STEP2(crc)                          \
+  do {                                                    \
+    crc = CRC32_u16(crc, absl::little_endian::Load16(p)); \
+    p += 2;                                               \
+  } while (0)
+#define ABSL_INTERNAL_STEP4(crc)                          \
+  do {                                                    \
+    crc = CRC32_u32(crc, absl::little_endian::Load32(p)); \
+    p += 4;                                               \
+  } while (0)
+#define ABSL_INTERNAL_STEP8(crc, data)                       \
+  do {                                                       \
+    crc = CRC32_u64(crc, absl::little_endian::Load64(data)); \
+    data += 8;                                               \
+  } while (0)
+#define ABSL_INTERNAL_STEP8BY2(crc0, crc1, p0, p1) \
+  do {                                             \
+    ABSL_INTERNAL_STEP8(crc0, p0);                 \
+    ABSL_INTERNAL_STEP8(crc1, p1);                 \
+  } while (0)
+#define ABSL_INTERNAL_STEP8BY3(crc0, crc1, crc2, p0, p1, p2) \
+  do {                                                       \
+    ABSL_INTERNAL_STEP8(crc0, p0);                           \
+    ABSL_INTERNAL_STEP8(crc1, p1);                           \
+    ABSL_INTERNAL_STEP8(crc2, p2);                           \
+  } while (0)
+
+uint32_t multiply(uint32_t a, uint32_t b) {
+  V128 shifts = V128_From2x64(0, 1);
+  V128 power = V128_From2x64(0, a);
+  V128 crc = V128_From2x64(0, b);
+  V128 res = V128_PMulLow(power, crc);
+
+  // Combine crc values
+  res = V128_ShiftLeft64(res, shifts);
+  return V128_Extract32<1>(res) ^ CRC32_u32(0, V128_Low64(res));
+}
+
+namespace {
+
+// Powers of crc32c polynomial, for faster ExtendByZeros.
+// Verified against folly:
+// folly/hash/detail/Crc32CombineDetail.cpp
+constexpr uint32_t kCRC32CPowers[] = {
+    0x82f63b78, 0x6ea2d55c, 0x18b8ea18, 0x510ac59a, 0xb82be955, 0xb8fdb1e7,
+    0x88e56f72, 0x74c360a4, 0xe4172b16, 0x0d65762a, 0x35d73a62, 0x28461564,
+    0xbf455269, 0xe2ea32dc, 0xfe7740e6, 0xf946610b, 0x3c204f8f, 0x538586e3,
+    0x59726915, 0x734d5309, 0xbc1ac763, 0x7d0722cc, 0xd289cabe, 0xe94ca9bc,
+    0x05b74f3f, 0xa51e1f42, 0x40000000, 0x20000000, 0x08000000, 0x00800000,
+    0x00008000, 0x82f63b78, 0x6ea2d55c, 0x18b8ea18, 0x510ac59a, 0xb82be955,
+    0xb8fdb1e7, 0x88e56f72, 0x74c360a4, 0xe4172b16, 0x0d65762a, 0x35d73a62,
+    0x28461564, 0xbf455269, 0xe2ea32dc, 0xfe7740e6, 0xf946610b, 0x3c204f8f,
+    0x538586e3, 0x59726915, 0x734d5309, 0xbc1ac763, 0x7d0722cc, 0xd289cabe,
+    0xe94ca9bc, 0x05b74f3f, 0xa51e1f42, 0x40000000, 0x20000000, 0x08000000,
+    0x00800000, 0x00008000,
+};
+
+}  // namespace
+
+// Compute a magic constant, so that multiplying by it is the same as
+// extending crc by length zeros.
+uint32_t CRC32AcceleratedX86ARMCombined::ComputeZeroConstant(
+    size_t length) const {
+  // Lowest 2 bits are handled separately in ExtendByZeroes
+  length >>= 2;
+
+  int index = absl::countr_zero(length);
+  uint32_t prev = kCRC32CPowers[index];
+  length &= length - 1;
+
+  while (length) {
+    // For each bit of length, extend by 2**n zeros.
+    index = absl::countr_zero(length);
+    prev = multiply(prev, kCRC32CPowers[index]);
+    length &= length - 1;
+  }
+  return prev;
+}
+
+void CRC32AcceleratedX86ARMCombined::ExtendByZeroes(uint32_t* crc,
+                                                    size_t length) const {
+  uint32_t val = *crc;
+  // Don't bother with multiplication for small length.
+  switch (length & 3) {
+    case 0:
+      break;
+    case 1:
+      val = CRC32_u8(val, 0);
+      break;
+    case 2:
+      val = CRC32_u16(val, 0);
+      break;
+    case 3:
+      val = CRC32_u8(val, 0);
+      val = CRC32_u16(val, 0);
+      break;
+  }
+  if (length > 3) {
+    val = multiply(val, ComputeZeroConstant(length));
+  }
+  *crc = val;
+}
+
+// Taken from Intel paper "Fast CRC Computation for iSCSI Polynomial Using CRC32
+// Instruction"
+// https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/crc-iscsi-polynomial-crc32-instruction-paper.pdf
+// We only need every 4th value, because we unroll loop by 4.
+constexpr uint64_t kClmulConstants[] = {
+    0x09e4addf8, 0x0ba4fc28e, 0x00d3b6092, 0x09e4addf8, 0x0ab7aff2a,
+    0x102f9b8a2, 0x0b9e02b86, 0x00d3b6092, 0x1bf2e8b8a, 0x18266e456,
+    0x0d270f1a2, 0x0ab7aff2a, 0x11eef4f8e, 0x083348832, 0x0dd7e3b0c,
+    0x0b9e02b86, 0x0271d9844, 0x1b331e26a, 0x06b749fb2, 0x1bf2e8b8a,
+    0x0e6fc4e6a, 0x0ce7f39f4, 0x0d7a4825c, 0x0d270f1a2, 0x026f6a60a,
+    0x12ed0daac, 0x068bce87a, 0x11eef4f8e, 0x1329d9f7e, 0x0b3e32c28,
+    0x0170076fa, 0x0dd7e3b0c, 0x1fae1cc66, 0x010746f3c, 0x086d8e4d2,
+    0x0271d9844, 0x0b3af077a, 0x093a5f730, 0x1d88abd4a, 0x06b749fb2,
+    0x0c9c8b782, 0x0cec3662e, 0x1ddffc5d4, 0x0e6fc4e6a, 0x168763fa6,
+    0x0b0cd4768, 0x19b1afbc4, 0x0d7a4825c, 0x123888b7a, 0x00167d312,
+    0x133d7a042, 0x026f6a60a, 0x000bcf5f6, 0x19d34af3a, 0x1af900c24,
+    0x068bce87a, 0x06d390dec, 0x16cba8aca, 0x1f16a3418, 0x1329d9f7e,
+    0x19fb2a8b0, 0x02178513a, 0x1a0f717c4, 0x0170076fa,
+};
+
+enum class CutoffStrategy {
+  // Use 3 CRC streams to fold into 1.
+  Fold3,
+  // Unroll CRC instructions for 64 bytes.
+  Unroll64CRC,
+};
+
+template <int num_crc_streams, int num_pclmul_streams, CutoffStrategy strategy>
+class CRC32AcceleratedX86ARMCombinedMultipleStreams
+    : public CRC32AcceleratedX86ARMCombined {
+  ABSL_ATTRIBUTE_HOT
+  void Extend(uint32_t* crc, const void* bytes, size_t length) const override {
+    static_assert(num_crc_streams >= 1 && num_crc_streams <= kMaxStreams,
+                  "Invalid number of crc streams");
+    static_assert(num_pclmul_streams >= 0 && num_pclmul_streams <= kMaxStreams,
+                  "Invalid number of pclmul streams");
+    const uint8_t* p = static_cast<const uint8_t*>(bytes);
+    const uint8_t* e = p + length;
+    uint32_t l = *crc;
+    uint64_t l64;
+
+    // We have dedicated instruction for 1,2,4 and 8 bytes.
+    if (length & 8) {
+      ABSL_INTERNAL_STEP8(l, p);
+      length &= ~8LL;
+    }
+    if (length & 4) {
+      ABSL_INTERNAL_STEP4(l);
+      length &= ~4LL;
+    }
+    if (length & 2) {
+      ABSL_INTERNAL_STEP2(l);
+      length &= ~2LL;
+    }
+    if (length & 1) {
+      ABSL_INTERNAL_STEP1(l);
+      length &= ~1LL;
+    }
+    if (length == 0) {
+      *crc = l;
+      return;
+    }
+    // length is now multiple of 16.
+
+    // For small blocks just run simple loop, because cost of combining multiple
+    // streams is significant.
+    if (strategy != CutoffStrategy::Unroll64CRC) {
+      if (length < kSmallCutoff) {
+        while (length >= 16) {
+          ABSL_INTERNAL_STEP8(l, p);
+          ABSL_INTERNAL_STEP8(l, p);
+          length -= 16;
+        }
+        *crc = l;
+        return;
+      }
+    }
+
+    // For medium blocks we run 3 crc streams and combine them as described in
+    // Intel paper above. Running 4th stream doesn't help, because crc
+    // instruction has latency 3 and throughput 1.
+    if (length < kMediumCutoff) {
+      l64 = l;
+      if (strategy == CutoffStrategy::Fold3) {
+        uint64_t l641 = 0;
+        uint64_t l642 = 0;
+        const int blockSize = 32;
+        int64_t bs = (e - p) / kGroupsSmall / blockSize;
+        const uint8_t* p1 = p + bs * blockSize;
+        const uint8_t* p2 = p1 + bs * blockSize;
+
+        for (int64_t i = 0; i < bs - 1; ++i) {
+          ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+          ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+          ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+          ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+        }
+        // Don't run crc on last 8 bytes.
+        ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+        ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+        ABSL_INTERNAL_STEP8BY3(l64, l641, l642, p, p1, p2);
+        ABSL_INTERNAL_STEP8BY2(l64, l641, p, p1);
+
+        V128 magic = *(reinterpret_cast<const V128*>(kClmulConstants) + bs - 1);
+
+        V128 tmp = V128_From2x64(0, l64);
+
+        V128 res1 = V128_PMulLow(tmp, magic);
+
+        tmp = V128_From2x64(0, l641);
+
+        V128 res2 = V128_PMul10(tmp, magic);
+        V128 x = V128_Xor(res1, res2);
+        l64 = V128_Low64(x) ^ absl::little_endian::Load64(p2);
+        l64 = CRC32_u64(l642, l64);
+
+        p = p2 + 8;
+      } else if (strategy == CutoffStrategy::Unroll64CRC) {
+        while ((e - p) >= 64) {
+          l64 = Process64BytesCRC(p, l64);
+          p += 64;
+        }
+      }
+    } else {
+      // There is a lot of data, we can ignore combine costs and run all
+      // requested streams (num_crc_streams + num_pclmul_streams),
+      // using prefetch. CRC and PCLMULQDQ use different cpu execution units,
+      // so on some cpus it makes sense to execute both of them for different
+      // streams.
+
+      // Point x at first 8-byte aligned byte in string.
+      const uint8_t* x = RoundUp<8>(p);
+      // Process bytes until p is 8-byte aligned, if that isn't past the end.
+      while (p != x) {
+        ABSL_INTERNAL_STEP1(l);
+      }
+
+      int64_t bs = (e - p) / (num_crc_streams + num_pclmul_streams) / 64;
+      const uint8_t* crc_streams[kMaxStreams];
+      const uint8_t* pclmul_streams[kMaxStreams];
+      // We are guaranteed to have at least one crc stream.
+      crc_streams[0] = p;
+      for (int i = 1; i < num_crc_streams; i++) {
+        crc_streams[i] = crc_streams[i - 1] + bs * 64;
+      }
+      pclmul_streams[0] = crc_streams[num_crc_streams - 1] + bs * 64;
+      for (int i = 1; i < num_pclmul_streams; i++) {
+        pclmul_streams[i] = pclmul_streams[i - 1] + bs * 64;
+      }
+
+      // Per stream crc sums.
+      uint64_t l64_crc[kMaxStreams] = {l};
+      uint64_t l64_pclmul[kMaxStreams] = {0};
+
+      // Peel first iteration, because PCLMULQDQ stream, needs setup.
+      for (int i = 0; i < num_crc_streams; i++) {
+        l64_crc[i] = Process64BytesCRC(crc_streams[i], l64_crc[i]);
+        crc_streams[i] += 16 * 4;
+      }
+
+      V128 partialCRC[kMaxStreams][4];
+      for (int i = 0; i < num_pclmul_streams; i++) {
+        partialCRC[i][0] = V128_LoadU(
+            reinterpret_cast<const V128*>(pclmul_streams[i] + 16 * 0));
+        partialCRC[i][1] = V128_LoadU(
+            reinterpret_cast<const V128*>(pclmul_streams[i] + 16 * 1));
+        partialCRC[i][2] = V128_LoadU(
+            reinterpret_cast<const V128*>(pclmul_streams[i] + 16 * 2));
+        partialCRC[i][3] = V128_LoadU(
+            reinterpret_cast<const V128*>(pclmul_streams[i] + 16 * 3));
+        pclmul_streams[i] += 16 * 4;
+      }
+
+      for (int64_t i = 1; i < bs; i++) {
+        // Prefetch data for next itterations.
+        for (int j = 0; j < num_crc_streams; j++) {
+          base_internal::PrefetchT0(
+              reinterpret_cast<const char*>(crc_streams[j] + kPrefetchHorizon));
+        }
+        for (int j = 0; j < num_pclmul_streams; j++) {
+          base_internal::PrefetchT0(reinterpret_cast<const char*>(
+              pclmul_streams[j] + kPrefetchHorizon));
+        }
+
+        // We process each stream in 64 byte blocks. This can be written as
+        // for (int i = 0; i < num_pclmul_streams; i++) {
+        //   Process64BytesPclmul(pclmul_streams[i], partialCRC[i]);
+        //   pclmul_streams[i] += 16 * 4;
+        // }
+        // for (int i = 0; i < num_crc_streams; i++) {
+        //   l64_crc[i] = Process64BytesCRC(crc_streams[i], l64_crc[i]);
+        //   crc_streams[i] += 16*4;
+        // }
+        // But unrolling and interleaving PCLMULQDQ and CRC blocks manually
+        // gives ~2% performance boost.
+        l64_crc[0] = Process64BytesCRC(crc_streams[0], l64_crc[0]);
+        crc_streams[0] += 16 * 4;
+        if (num_pclmul_streams > 0) {
+          Process64BytesPclmul(pclmul_streams[0], partialCRC[0]);
+          pclmul_streams[0] += 16 * 4;
+        }
+        if (num_crc_streams > 1) {
+          l64_crc[1] = Process64BytesCRC(crc_streams[1], l64_crc[1]);
+          crc_streams[1] += 16 * 4;
+        }
+        if (num_pclmul_streams > 1) {
+          Process64BytesPclmul(pclmul_streams[1], partialCRC[1]);
+          pclmul_streams[1] += 16 * 4;
+        }
+        if (num_crc_streams > 2) {
+          l64_crc[2] = Process64BytesCRC(crc_streams[2], l64_crc[2]);
+          crc_streams[2] += 16 * 4;
+        }
+        if (num_pclmul_streams > 2) {
+          Process64BytesPclmul(pclmul_streams[2], partialCRC[2]);
+          pclmul_streams[2] += 16 * 4;
+        }
+      }
+
+      // PCLMULQDQ based streams require special final step;
+      // CRC based don't.
+      for (int i = 0; i < num_pclmul_streams; i++) {
+        l64_pclmul[i] = FinalizePclmulStream(partialCRC[i]);
+      }
+
+      // Combine all streams into single result.
+      uint32_t magic = ComputeZeroConstant(bs * 64);
+      l64 = l64_crc[0];
+      for (int i = 1; i < num_crc_streams; i++) {
+        l64 = multiply(l64, magic);
+        l64 ^= l64_crc[i];
+      }
+      for (int i = 0; i < num_pclmul_streams; i++) {
+        l64 = multiply(l64, magic);
+        l64 ^= l64_pclmul[i];
+      }
+
+      // Update p.
+      if (num_pclmul_streams > 0) {
+        p = pclmul_streams[num_pclmul_streams - 1];
+      } else {
+        p = crc_streams[num_crc_streams - 1];
+      }
+    }
+    l = l64;
+
+    while ((e - p) >= 16) {
+      ABSL_INTERNAL_STEP8(l, p);
+      ABSL_INTERNAL_STEP8(l, p);
+    }
+    // Process the last few bytes
+    while (p != e) {
+      ABSL_INTERNAL_STEP1(l);
+    }
+
+#undef ABSL_INTERNAL_STEP8BY3
+#undef ABSL_INTERNAL_STEP8BY2
+#undef ABSL_INTERNAL_STEP8
+#undef ABSL_INTERNAL_STEP4
+#undef ABSL_INTERNAL_STEP2
+#undef ABSL_INTERNAL_STEP1
+
+    *crc = l;
+  }
+
+ private:
+  // Update partialCRC with crc of 64 byte block. Calling FinalizePclmulStream
+  // would produce a single crc checksum, but it is expensive. PCLMULQDQ has a
+  // high latency, so we run 4 128-bit partial checksums that can be reduced to
+  // a single value by FinalizePclmulStream later. Computing crc for arbitrary
+  // polynomialas with PCLMULQDQ is described in Intel paper "Fast CRC
+  // Computation for Generic Polynomials Using PCLMULQDQ Instruction"
+  // https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf
+  // We are applying it to CRC32C polynomial.
+  ABSL_ATTRIBUTE_ALWAYS_INLINE void Process64BytesPclmul(
+      const uint8_t* p, V128* partialCRC) const {
+    V128 loopMultiplicands = V128_Load(reinterpret_cast<const V128*>(k1k2));
+
+    V128 partialCRC1 = partialCRC[0];
+    V128 partialCRC2 = partialCRC[1];
+    V128 partialCRC3 = partialCRC[2];
+    V128 partialCRC4 = partialCRC[3];
+
+    V128 tmp1 = V128_PMulHi(partialCRC1, loopMultiplicands);
+    V128 tmp2 = V128_PMulHi(partialCRC2, loopMultiplicands);
+    V128 tmp3 = V128_PMulHi(partialCRC3, loopMultiplicands);
+    V128 tmp4 = V128_PMulHi(partialCRC4, loopMultiplicands);
+    V128 data1 = V128_LoadU(reinterpret_cast<const V128*>(p + 16 * 0));
+    V128 data2 = V128_LoadU(reinterpret_cast<const V128*>(p + 16 * 1));
+    V128 data3 = V128_LoadU(reinterpret_cast<const V128*>(p + 16 * 2));
+    V128 data4 = V128_LoadU(reinterpret_cast<const V128*>(p + 16 * 3));
+    partialCRC1 = V128_PMulLow(partialCRC1, loopMultiplicands);
+    partialCRC2 = V128_PMulLow(partialCRC2, loopMultiplicands);
+    partialCRC3 = V128_PMulLow(partialCRC3, loopMultiplicands);
+    partialCRC4 = V128_PMulLow(partialCRC4, loopMultiplicands);
+    partialCRC1 = V128_Xor(tmp1, partialCRC1);
+    partialCRC2 = V128_Xor(tmp2, partialCRC2);
+    partialCRC3 = V128_Xor(tmp3, partialCRC3);
+    partialCRC4 = V128_Xor(tmp4, partialCRC4);
+    partialCRC1 = V128_Xor(partialCRC1, data1);
+    partialCRC2 = V128_Xor(partialCRC2, data2);
+    partialCRC3 = V128_Xor(partialCRC3, data3);
+    partialCRC4 = V128_Xor(partialCRC4, data4);
+    partialCRC[0] = partialCRC1;
+    partialCRC[1] = partialCRC2;
+    partialCRC[2] = partialCRC3;
+    partialCRC[3] = partialCRC4;
+  }
+
+  // Reduce partialCRC produced by Process64BytesPclmul into a single value,
+  // that represents crc checksum of all the processed bytes.
+  ABSL_ATTRIBUTE_ALWAYS_INLINE uint64_t
+  FinalizePclmulStream(V128* partialCRC) const {
+    V128 partialCRC1 = partialCRC[0];
+    V128 partialCRC2 = partialCRC[1];
+    V128 partialCRC3 = partialCRC[2];
+    V128 partialCRC4 = partialCRC[3];
+
+    // Combine 4 vectors of partial crc into a single vector.
+    V128 reductionMultiplicands =
+        V128_Load(reinterpret_cast<const V128*>(k5k6));
+
+    V128 low = V128_PMulLow(reductionMultiplicands, partialCRC1);
+    V128 high = V128_PMulHi(reductionMultiplicands, partialCRC1);
+
+    partialCRC1 = V128_Xor(low, high);
+    partialCRC1 = V128_Xor(partialCRC1, partialCRC2);
+
+    low = V128_PMulLow(reductionMultiplicands, partialCRC3);
+    high = V128_PMulHi(reductionMultiplicands, partialCRC3);
+
+    partialCRC3 = V128_Xor(low, high);
+    partialCRC3 = V128_Xor(partialCRC3, partialCRC4);
+
+    reductionMultiplicands = V128_Load(reinterpret_cast<const V128*>(k3k4));
+
+    low = V128_PMulLow(reductionMultiplicands, partialCRC1);
+    high = V128_PMulHi(reductionMultiplicands, partialCRC1);
+    V128 fullCRC = V128_Xor(low, high);
+    fullCRC = V128_Xor(fullCRC, partialCRC3);
+
+    // Reduce fullCRC into scalar value.
+    reductionMultiplicands = V128_Load(reinterpret_cast<const V128*>(k5k6));
+
+    V128 mask = V128_Load(reinterpret_cast<const V128*>(kMask));
+
+    V128 tmp = V128_PMul01(reductionMultiplicands, fullCRC);
+    fullCRC = V128_ShiftRight<8>(fullCRC);
+    fullCRC = V128_Xor(fullCRC, tmp);
+
+    reductionMultiplicands = V128_Load(reinterpret_cast<const V128*>(k7k0));
+
+    tmp = V128_ShiftRight<4>(fullCRC);
+    fullCRC = V128_And(fullCRC, mask);
+    fullCRC = V128_PMulLow(reductionMultiplicands, fullCRC);
+    fullCRC = V128_Xor(tmp, fullCRC);
+
+    reductionMultiplicands = V128_Load(reinterpret_cast<const V128*>(kPoly));
+
+    tmp = V128_And(fullCRC, mask);
+    tmp = V128_PMul01(reductionMultiplicands, tmp);
+    tmp = V128_And(tmp, mask);
+    tmp = V128_PMulLow(reductionMultiplicands, tmp);
+
+    fullCRC = V128_Xor(tmp, fullCRC);
+
+    return V128_Extract32<1>(fullCRC);
+  }
+
+  // Update crc with 64 bytes of data from p.
+  ABSL_ATTRIBUTE_ALWAYS_INLINE uint64_t Process64BytesCRC(const uint8_t* p,
+                                                          uint64_t crc) const {
+    for (int i = 0; i < 8; i++) {
+      crc = CRC32_u64(crc, absl::little_endian::Load64(p));
+      p += 8;
+    }
+    return crc;
+  }
+
+  // Generated by crc32c_x86_test --crc32c_generate_constants=true
+  // and verified against constants in linux kernel for S390:
+  // https://github.com/torvalds/linux/blob/master/arch/s390/crypto/crc32le-vx.S
+  alignas(16) static constexpr uint64_t k1k2[2] = {0x0740eef02, 0x09e4addf8};
+  alignas(16) static constexpr uint64_t k3k4[2] = {0x1384aa63a, 0x0ba4fc28e};
+  alignas(16) static constexpr uint64_t k5k6[2] = {0x0f20c0dfe, 0x14cd00bd6};
+  alignas(16) static constexpr uint64_t k7k0[2] = {0x0dd45aab8, 0x000000000};
+  alignas(16) static constexpr uint64_t kPoly[2] = {0x105ec76f0, 0x0dea713f1};
+  alignas(16) static constexpr uint32_t kMask[4] = {~0u, 0u, ~0u, 0u};
+
+  // Medium runs of bytes are broken into groups of kGroupsSmall blocks of same
+  // size. Each group is CRCed in parallel then combined at the end of the
+  // block.
+  static constexpr int kGroupsSmall = 3;
+  // For large runs we use up to kMaxStreams blocks computed with CRC
+  // instruction, and up to kMaxStreams blocks computed with PCLMULQDQ, which
+  // are combined in the end.
+  static constexpr int kMaxStreams = 3;
+};
+
+}  // namespace
+
+// Intel processors with SSE4.2 have an instruction for one particular
+// 32-bit CRC polynomial:  crc32c
+CRCImpl* TryNewCRC32AcceleratedX86ARMCombined() {
+  CpuType type = GetCpuType();
+  switch (type) {
+    case CpuType::kIntelHaswell:
+    case CpuType::kAmdRome:
+    case CpuType::kAmdNaples:
+    case CpuType::kAmdMilan:
+      return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+          3, 1, CutoffStrategy::Fold3>();
+    // PCLMULQDQ is fast, use combined PCLMULQDQ + CRC implementation.
+    case CpuType::kIntelCascadelakeXeon:
+    case CpuType::kIntelSkylakeXeon:
+    case CpuType::kIntelBroadwell:
+    case CpuType::kIntelSkylake:
+      return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+          3, 2, CutoffStrategy::Fold3>();
+    // PCLMULQDQ is slow, don't use it.
+    case CpuType::kIntelIvybridge:
+    case CpuType::kIntelSandybridge:
+    case CpuType::kIntelWestmere:
+      return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+          3, 0, CutoffStrategy::Fold3>();
+    case CpuType::kArmNeoverseN1:
+      return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+          1, 1, CutoffStrategy::Unroll64CRC>();
+#if defined(__aarch64__)
+    default:
+      // Not all ARM processors support the needed instructions, so check here
+      // before trying to use an accelerated implementation.
+      if (SupportsArmCRC32PMULL()) {
+        return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+            1, 1, CutoffStrategy::Unroll64CRC>();
+      } else {
+        return nullptr;
+      }
+#else
+    default:
+      // Something else, play it safe and assume slow PCLMULQDQ.
+      return new CRC32AcceleratedX86ARMCombinedMultipleStreams<
+          3, 0, CutoffStrategy::Fold3>();
+#endif
+  }
+}
+
+std::vector<std::unique_ptr<CRCImpl>> NewCRC32AcceleratedX86ARMCombinedAll() {
+  auto ret = std::vector<std::unique_ptr<CRCImpl>>();
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 0, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 1, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 2, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 3, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 0, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 1, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 2, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 3, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 0, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 1, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 2, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 3, CutoffStrategy::Fold3>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 0, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 1, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 2, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    1, 3, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 0, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 1, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 2, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    2, 3, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 0, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 1, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 2, CutoffStrategy::Unroll64CRC>>());
+  ret.push_back(absl::make_unique<CRC32AcceleratedX86ARMCombinedMultipleStreams<
+                    3, 3, CutoffStrategy::Unroll64CRC>>());
+
+  return ret;
+}
+
+#else  // !ABSL_INTERNAL_CAN_USE_SIMD_CRC32C
+
+std::vector<std::unique_ptr<CRCImpl>> NewCRC32AcceleratedX86ARMCombinedAll() {
+  return std::vector<std::unique_ptr<CRCImpl>>();
+}
+
+// no hardware acceleration available
+CRCImpl* TryNewCRC32AcceleratedX86ARMCombined() { return nullptr; }
+
+#endif
+
+}  // namespace crc_internal
+ABSL_NAMESPACE_END
+}  // namespace absl