Implement support for Intel crc32 instruction (SSE 4.2)

This change authored by vadimskipin and submitted via:

    https://github.com/google/leveldb/pull/309

Changes made to support iOS builds and other architectures
without support for SSE 4.2.

db_bench reports original crc32 speed at:

    crc32c : 3.610 micros/op; 1082.0 MB/s (4K per op)

with this change performance has increased to:

    crc32c : 0.843 micros/op; 4633.6 MB/s (4K per op)

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148694935

3 files changed, 133 insertions, 0 deletions

diff --git a/port/port_example.h b/port/port_example.h
index ab9e489..97bd669 100644
--- a/port/port_example.h
+++ b/port/port_example.h
@@ -129,6 +129,12 @@ extern bool Snappy_Uncompress(const char* input_data, size_t input_length,
 // The concatenation of all "data[0,n-1]" fragments is the heap profile.
 extern bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg);
 
+// Extend the CRC to include the first n bytes of buf.
+//
+// Returns zero if the CRC cannot be extended using acceleration, else returns
+// the newly extended CRC value (which may also be zero).
+uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size);
+
 }  // namespace port
 }  // namespace leveldb
 
diff --git a/port/port_posix.h b/port/port_posix.h
index 89fc222..d67ab68 100644
--- a/port/port_posix.h
+++ b/port/port_posix.h
@@ -148,6 +148,8 @@ inline bool GetHeapProfile(void (*func)(void*, const char*, int), void* arg) {
   return false;
 }
 
+uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size);
+
 } // namespace port
 } // namespace leveldb
 
diff --git a/port/port_posix_sse.cc b/port/port_posix_sse.cc
new file mode 100644
index 0000000..57ec8fe
--- /dev/null
+++ b/port/port_posix_sse.cc
@@ -0,0 +1,125 @@
+// Copyright 2016 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+//
+// A portable implementation of crc32c, optimized to handle
+// four bytes at a time.
+//
+// In a separate source file to allow this accelerated CRC32C function to be
+// compiled with the appropriate compiler flags to enable x86 SSE 4.2
+// instructions.
+
+#include <stdint.h>
+#include <string.h>
+#include "port/port.h"
+
+#if defined(LEVELDB_PLATFORM_POSIX_SSE)
+
+#if defined(_MSC_VER)
+#include <intrin.h>
+#elif defined(__GNUC__) && defined(__SSE4_2__)
+#include <nmmintrin.h>
+#include <cpuid.h>
+#endif
+
+#endif  // defined(LEVELDB_PLATFORM_POSIX_SSE)
+
+namespace leveldb {
+namespace port {
+
+#if defined(LEVELDB_PLATFORM_POSIX_SSE)
+
+// Used to fetch a naturally-aligned 32-bit word in little endian byte-order
+static inline uint32_t LE_LOAD32(const uint8_t *p) {
+  // SSE is x86 only, so ensured that |p| is always little-endian.
+  uint32_t word;
+  memcpy(&word, p, sizeof(word));
+  return word;
+}
+
+// Used to fetch a naturally-aligned 64-bit word in little endian byte-order
+static inline uint64_t LE_LOAD64(const uint8_t *p) {
+  uint64_t dword;
+  memcpy(&dword, p, sizeof(dword));
+  return dword;
+}
+
+static inline bool HaveSSE42() {
+#if defined(_MSC_VER)
+  int cpu_info[4];
+  __cpuid(cpu_info, 1);
+  return (cpu_info[2] & (1 << 20)) != 0;
+#elif defined(__GNUC__)
+  unsigned int eax, ebx, ecx, edx;
+  __get_cpuid(1, &eax, &ebx, &ecx, &edx);
+  return (ecx & (1 << 20)) != 0;
+#else
+  return false;
+#endif
+}
+
+#endif  // defined(LEVELDB_PLATFORM_POSIX_SSE)
+
+// For further improvements see Intel publication at:
+// http://download.intel.com/design/intarch/papers/323405.pdf
+uint32_t AcceleratedCRC32C(uint32_t crc, const char* buf, size_t size) {
+#if !defined(LEVELDB_PLATFORM_POSIX_SSE)
+  return 0;
+#else
+  static bool have = HaveSSE42();
+  if (!have) {
+    return 0;
+  }
+
+  const uint8_t *p = reinterpret_cast<const uint8_t *>(buf);
+  const uint8_t *e = p + size;
+  uint32_t l = crc ^ 0xffffffffu;
+
+#define STEP1 do {                              \
+    l = _mm_crc32_u8(l, *p++);                  \
+} while (0)
+#define STEP4 do {                              \
+    l = _mm_crc32_u32(l, LE_LOAD32(p));         \
+    p += 4;                                     \
+} while (0)
+#define STEP8 do {                              \
+    l = _mm_crc32_u64(l, LE_LOAD64(p));         \
+    p += 8;                                     \
+} while (0)
+
+  if (size > 16) {
+    // Process unaligned bytes
+    for (unsigned int i = reinterpret_cast<uintptr_t>(p) % 8; i; --i) {
+      STEP1;
+    }
+
+    // _mm_crc32_u64 is only available on x64.
+#if defined(_M_X64) || defined(__x86_64__)
+    // Process 8 bytes at a time
+    while ((e-p) >= 8) {
+      STEP8;
+    }
+    // Process 4 bytes at a time
+    if ((e-p) >= 4) {
+      STEP4;
+    }
+#else  // !(defined(_M_X64) || defined(__x86_64__))
+    // Process 4 bytes at a time
+    while ((e-p) >= 4) {
+      STEP4;
+    }
+#endif  // defined(_M_X64) || defined(__x86_64__)
+  }
+  // Process the last few bytes
+  while (p != e) {
+    STEP1;
+  }
+#undef STEP8
+#undef STEP4
+#undef STEP1
+  return l ^ 0xffffffffu;
+#endif  // defined(LEVELDB_PLATFORM_POSIX_SSE)
+}
+
+}  // namespace port
+}  // namespace leveldb