diff --git a/llvm/lib/Support/CRC.cpp b/llvm/lib/Support/CRC.cpp
index fd98f3a..7c008d3 100644
--- a/llvm/lib/Support/CRC.cpp
+++ b/llvm/lib/Support/CRC.cpp
@@ -6,63 +6,94 @@
 //
 //===----------------------------------------------------------------------===//
 //
-//  This file implements llvm::crc32 function.
+// This file contains implementations of CRC functions.
+//
+// The implementation technique is the one mentioned in:
+// D. V. Sarwate. 1988. Computation of cyclic redundancy checks via table
+// look-up. Commun. ACM 31, 8 (August 1988)
+//
+// See also Ross N. Williams "A Painless Guide to CRC Error Detection
+// Algorithms" (https://zlib.net/crc_v3.txt) or Hacker's Delight (2nd ed.)
+// Chapter 14 (Figure 14-7 in particular) for how the algorithm works.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/CRC.h"
+
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/Config/config.h"
-#include "llvm/ADT/StringRef.h"
-#include "llvm/Support/Threading.h"
-#include <array>
 
 using namespace llvm;
 
 #if LLVM_ENABLE_ZLIB == 0 || !HAVE_ZLIB_H
-using CRC32Table = std::array<uint32_t, 256>;
 
-static void initCRC32Table(CRC32Table *Tbl) {
-  auto Shuffle = [](uint32_t V) {
-    return (V & 1) ? (V >> 1) ^ 0xEDB88320U : V >> 1;
-  };
+static const uint32_t CRCTable[256] = {
+    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
+    0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
+    0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
+    0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
+    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
+    0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
+    0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
+    0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
+    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
+    0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
+    0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
+    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
+    0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
+    0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
+    0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
+    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
+    0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
+    0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
+    0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
+    0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
+    0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
+    0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
+    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
+    0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
+    0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
+    0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
+    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
+    0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
+    0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
+    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
+    0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
+    0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
+    0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
+    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
+    0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
+    0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
+    0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
+    0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
+    0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d};
 
-  for (size_t I = 0; I < Tbl->size(); ++I) {
-    uint32_t V = Shuffle(I);
-    V = Shuffle(V);
-    V = Shuffle(V);
-    V = Shuffle(V);
-    V = Shuffle(V);
-    V = Shuffle(V);
-    V = Shuffle(V);
-    (*Tbl)[I] = Shuffle(V);
-  }
-}
-
-uint32_t llvm::crc32(uint32_t CRC, StringRef S) {
-  static llvm::once_flag InitFlag;
-  static CRC32Table Tbl;
-  llvm::call_once(InitFlag, initCRC32Table, &Tbl);
-
-  const uint8_t *P = reinterpret_cast<const uint8_t *>(S.data());
-  size_t Len = S.size();
+uint32_t llvm::crc32(uint32_t CRC, ArrayRef<uint8_t> Data) {
   CRC ^= 0xFFFFFFFFU;
-  for (; Len >= 8; Len -= 8) {
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
+  for (uint8_t Byte : Data) {
+    int TableIdx = (CRC ^ Byte) & 0xff;
+    CRC = CRCTable[TableIdx] ^ (CRC >> 8);
   }
-  while (Len--)
-    CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
   return CRC ^ 0xFFFFFFFFU;
 }
+
 #else
+
 #include <zlib.h>
-uint32_t llvm::crc32(uint32_t CRC, StringRef S) {
-  return ::crc32(CRC, (const Bytef *)S.data(), S.size());
+uint32_t llvm::crc32(uint32_t CRC, ArrayRef<uint8_t> Data) {
+  return ::crc32(CRC, (const Bytef *)Data.data(), Data.size());
 }
+
 #endif
+
+uint32_t llvm::crc32(ArrayRef<uint8_t> Data) { return crc32(0, Data); }
+
+void JamCRC::update(ArrayRef<uint8_t> Data) {
+  CRC ^= 0xFFFFFFFFU; // Undo CRC-32 Init.
+  CRC = crc32(CRC, Data);
+  CRC ^= 0xFFFFFFFFU; // Undo CRC-32 XorOut.
+}