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Unified Diff: xz/src/liblzma/check/crc32_fast.c

Issue 2869016: Add an unpatched version of xz, XZ Utils, to /trunk/deps/third_party (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/deps/third_party/
Patch Set: Created 10 years, 6 months ago
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Index: xz/src/liblzma/check/crc32_fast.c
===================================================================
--- xz/src/liblzma/check/crc32_fast.c (revision 0)
+++ xz/src/liblzma/check/crc32_fast.c (revision 0)
@@ -0,0 +1,82 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file crc32.c
+/// \brief CRC32 calculation
+///
+/// Calculate the CRC32 using the slice-by-eight algorithm.
+/// It is explained in this document:
+/// http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf
+/// The code in this file is not the same as in Intel's paper, but
+/// the basic principle is identical.
+//
+// Author: Lasse Collin
+//
+// This file has been put into the public domain.
+// You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include "check.h"
+#include "crc_macros.h"
+
+
+// If you make any changes, do some bench marking! Seemingly unrelated
+// changes can very easily ruin the performance (and very probably is
+// very compiler dependent).
+extern LZMA_API(uint32_t)
+lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
+{
+ crc = ~crc;
+
+#ifdef WORDS_BIGENDIAN
+ crc = bswap32(crc);
+#endif
+
+ if (size > 8) {
+ // Fix the alignment, if needed. The if statement above
+ // ensures that this won't read past the end of buf[].
+ while ((uintptr_t)(buf) & 7) {
+ crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
+ --size;
+ }
+
+ // Calculate the position where to stop.
+ const uint8_t *const limit = buf + (size & ~(size_t)(7));
+
+ // Calculate how many bytes must be calculated separately
+ // before returning the result.
+ size &= (size_t)(7);
+
+ // Calculate the CRC32 using the slice-by-eight algorithm.
+ while (buf < limit) {
+ crc ^= *(const uint32_t *)(buf);
+ buf += 4;
+
+ crc = lzma_crc32_table[7][A(crc)]
+ ^ lzma_crc32_table[6][B(crc)]
+ ^ lzma_crc32_table[5][C(crc)]
+ ^ lzma_crc32_table[4][D(crc)];
+
+ const uint32_t tmp = *(const uint32_t *)(buf);
+ buf += 4;
+
+ // At least with some compilers, it is critical for
+ // performance, that the crc variable is XORed
+ // between the two table-lookup pairs.
+ crc = lzma_crc32_table[3][A(tmp)]
+ ^ lzma_crc32_table[2][B(tmp)]
+ ^ crc
+ ^ lzma_crc32_table[1][C(tmp)]
+ ^ lzma_crc32_table[0][D(tmp)];
+ }
+ }
+
+ while (size-- != 0)
+ crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
+
+#ifdef WORDS_BIGENDIAN
+ crc = bswap32(crc);
+#endif
+
+ return ~crc;
+}
Property changes on: xz/src/liblzma/check/crc32_fast.c
___________________________________________________________________
Added: svn:eol-style
+ LF
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