X-Git-Url: https://pd.if.org/git/?a=blobdiff_plain;f=lzma%2Fcheck%2Fcrc32_fast.c;fp=lzma%2Fcheck%2Fcrc32_fast.c;h=3de02638d776326c655795cf0cdba3bb5c992949;hb=32b8a6b26ed8843828e03e505d2256960bda0980;hp=0000000000000000000000000000000000000000;hpb=d48fc23a4bcf8ca3c406d6e8c8a6f8c6b0fa2f1e;p=zpackage

diff --git a/lzma/check/crc32_fast.c b/lzma/check/crc32_fast.c
new file mode 100644
index 0000000..3de0263
--- /dev/null
+++ b/lzma/check/crc32_fast.c
@@ -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 benchmarking! 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;
+}