Unify the two CRC implementations

David added the JamCRC implementation in r246590. More recently, Eugene
added a CRC-32 implementation in r357901, which falls back to zlib's
crc32 function if present.

These checksums are essentially the same, so having multiple
implementations seems unnecessary. This replaces the CRC-32
implementation with the simpler one from JamCRC, and implements the
JamCRC interface in terms of CRC-32 since this means it can use zlib's
implementation when available, saving a few bytes and potentially making
it faster.

JamCRC took an ArrayRef<char> argument, and CRC-32 took a StringRef.
This patch changes it to ArrayRef<uint8_t> which I think is the best
choice, and simplifies a few of the callers nicely.

Differential revision: https://reviews.llvm.org/D68570

llvm-svn: 374148

1 files changed, 19 insertions, 4 deletions

diff --git a/llvm/unittests/Support/CRCTest.cpp b/llvm/unittests/Support/CRCTest.cpp
index 71afb0a4789..8e2cb2c5e78 100644
--- a/llvm/unittests/Support/CRCTest.cpp
+++ b/llvm/unittests/Support/CRCTest.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/CRC.h"
+#include "llvm/ADT/StringExtras.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
@@ -18,12 +19,26 @@ using namespace llvm;
 namespace {
 
 TEST(CRCTest, CRC32) {
-  EXPECT_EQ(0x414FA339U,
-            llvm::crc32(
-                0, StringRef("The quick brown fox jumps over the lazy dog")));
+  EXPECT_EQ(0x414FA339U, llvm::crc32(arrayRefFromStringRef(
+                             "The quick brown fox jumps over the lazy dog")));
+
   // CRC-32/ISO-HDLC test vector
   // http://reveng.sourceforge.net/crc-catalogue/17plus.htm#crc.cat.crc-32c
-  EXPECT_EQ(0xCBF43926U, llvm::crc32(0, StringRef("123456789")));
+  EXPECT_EQ(0xCBF43926U, llvm::crc32(arrayRefFromStringRef("123456789")));
+
+  // Check the CRC-32 of each byte value, exercising all of CRCTable.
+  for (int i = 0; i < 256; i++) {
+    // Compute CRCTable[i] using Hacker's Delight (2nd ed.) Figure 14-7.
+    uint32_t crc = i;
+    for (int j = 7; j >= 0; j--) {
+      uint32_t mask = -(crc & 1);
+      crc = (crc >> 1) ^ (0xEDB88320 & mask);
+    }
+
+    // CRCTable[i] is the CRC-32 of i without the initial and final bit flips.
+    uint8_t byte = i;
+    EXPECT_EQ(crc, ~llvm::crc32(0xFFFFFFFFU, byte));
+  }
 }
 
 } // end anonymous namespace