Reorganize our CRC source files again.

Now that we use CRC-32C in WAL and the control file, the "traditional" and "legacy" CRC-32 variants are not used in any frontend programs anymore. Move the code for those back from src/common to src/backend/utils/hash. Also move the slicing-by-8 implementation (back) to src/port. This is in preparation for next patch that will add another implementation that uses Intel SSE 4.2 instructions to calculate CRC-32C, where available.
2025-07-14 08:21:07 +03:00 · 2015-04-14 17:03:42 +03:00
parent d577bb868d
commit 4f700bcd20
25 changed files with 211 additions and 181 deletions
--- a/src/include/utils/pg_crc.h
+++ b/src/include/utils/pg_crc.h
@ -0,0 +1,107 @@
+/*
+ * pg_crc.h
+ *
+ * PostgreSQL CRC support
+ *
+ * See Ross Williams' excellent introduction
+ * A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS, available from
+ * http://www.ross.net/crc/ or several other net sites.
+ *
+ * We have three slightly different variants of a 32-bit CRC calculation:
+ * CRC-32C (Castagnoli polynomial), CRC-32 (Ethernet polynomial), and a legacy
+ * CRC-32 version that uses the lookup table in a funny way. They all consist
+ * of four macros:
+ *
+ * INIT_<variant>(crc)
+ *		Initialize a CRC accumulator
+ *
+ * COMP_<variant>(crc, data, len)
+ *		Accumulate some (more) bytes into a CRC
+ *
+ * FIN_<variant>(crc)
+ *		Finish a CRC calculation
+ *
+ * EQ_<variant>(c1, c2)
+ *		Check for equality of two CRCs.
+ *
+ * The CRC-32C variant is in port/pg_crc32c.h.
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/utils/pg_crc.h
+ */
+#ifndef PG_CRC_H
+#define PG_CRC_H
+
+typedef uint32 pg_crc32;
+
+/*
+ * CRC-32, the same used e.g. in Ethernet.
+ *
+ * This is currently only used in ltree and hstore contrib modules. It uses
+ * the same lookup table as the legacy algorithm below. New code should
+ * use the Castagnoli version instead.
+ */
+#define INIT_TRADITIONAL_CRC32(crc) ((crc) = 0xFFFFFFFF)
+#define FIN_TRADITIONAL_CRC32(crc)	((crc) ^= 0xFFFFFFFF)
+#define COMP_TRADITIONAL_CRC32(crc, data, len)	\
+	COMP_CRC32_NORMAL_TABLE(crc, data, len, pg_crc32_table)
+#define EQ_TRADITIONAL_CRC32(c1, c2) ((c1) == (c2))
+
+/* Sarwate's algorithm, for use with a "normal" lookup table */
+#define COMP_CRC32_NORMAL_TABLE(crc, data, len, table)			  \
+do {															  \
+	const unsigned char *__data = (const unsigned char *) (data); \
+	uint32		__len = (len); \
+\
+	while (__len-- > 0) \
+	{ \
+		int		__tab_index = ((int) (crc) ^ *__data++) & 0xFF; \
+		(crc) = table[__tab_index] ^ ((crc) >> 8); \
+	} \
+} while (0)
+
+/*
+ * The CRC algorithm used for WAL et al in pre-9.5 versions.
+ *
+ * This closely resembles the normal CRC-32 algorithm, but is subtly
+ * different. Using Williams' terms, we use the "normal" table, but with
+ * "reflected" code. That's bogus, but it was like that for years before
+ * anyone noticed. It does not correspond to any polynomial in a normal CRC
+ * algorithm, so it's not clear what the error-detection properties of this
+ * algorithm actually are.
+ *
+ * We still need to carry this around because it is used in a few on-disk
+ * structures that need to be pg_upgradeable. It should not be used in new
+ * code.
+ */
+#define INIT_LEGACY_CRC32(crc) ((crc) = 0xFFFFFFFF)
+#define FIN_LEGACY_CRC32(crc)	((crc) ^= 0xFFFFFFFF)
+#define COMP_LEGACY_CRC32(crc, data, len)	\
+	COMP_CRC32_REFLECTED_TABLE(crc, data, len, pg_crc32_table)
+#define EQ_LEGACY_CRC32(c1, c2) ((c1) == (c2))
+
+/*
+ * Sarwate's algorithm, for use with a "reflected" lookup table (but in the
+ * legacy algorithm, we actually use it on a "normal" table, see above)
+ */
+#define COMP_CRC32_REFLECTED_TABLE(crc, data, len, table) \
+do {															  \
+	const unsigned char *__data = (const unsigned char *) (data); \
+	uint32		__len = (len); \
+\
+	while (__len-- > 0) \
+	{ \
+		int		__tab_index = ((int) ((crc) >> 24) ^ *__data++) & 0xFF;	\
+		(crc) = table[__tab_index] ^ ((crc) << 8); \
+	} \
+} while (0)
+
+/*
+ * Constant table for the CRC-32 polynomials. The same table is used by both
+ * the normal and traditional variants.
+ */
+extern PGDLLIMPORT const uint32 pg_crc32_table[256];
+
+#endif   /* PG_CRC_H */