text: /*-------------------------------------------------------------------------
   *
   * pg_crc32c.h
   *	  Routines for computing CRC-32C checksums.
   *
   * The speed of CRC-32C calculation has a big impact on performance, so we
   * jump through some hoops to get the best implementation for each
   * platform. Some CPU architectures have special instructions for speeding
   * up CRC calculations (e.g. Intel SSE 4.2), on other platforms we use the
   * Slicing-by-8 algorithm which uses lookup tables.
   *
   * The public interface consists of four macros:
   *
   * INIT_CRC32C(crc)
   *		Initialize a CRC accumulator
   *
   * COMP_CRC32C(crc, data, len)
   *		Accumulate some (more) bytes into a CRC
   *
   * FIN_CRC32C(crc)
   *		Finish a CRC calculation
   *
   * EQ_CRC32C(c1, c2)
   *		Check for equality of two CRCs.
   *
   * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * src/include/port/pg_crc32c.h
   *
   *-------------------------------------------------------------------------
   */
  #ifndef PG_CRC32C_H
  #define PG_CRC32C_H
  
  #include "port/pg_bswap.h"
  
  typedef uint32 pg_crc32c;
  
  /* The INIT and EQ macros are the same for all implementations. */
  #define INIT_CRC32C(crc) ((crc) = 0xFFFFFFFF)
  #define EQ_CRC32C(c1, c2) ((c1) == (c2))
  
  #if defined(USE_SSE42_CRC32C)
  /* Use SSE4.2 instructions. */
  #define COMP_CRC32C(crc, data, len) \
  	((crc) = pg_comp_crc32c_sse42((crc), (data), (len)))
  #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
  
  extern pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len);
  
  #elif defined(USE_SSE42_CRC32C_WITH_RUNTIME_CHECK)
  /*
   * Use SSE4.2 instructions, but perform a runtime check first to check that
   * they are available.
   */
  #define COMP_CRC32C(crc, data, len) \
  	((crc) = pg_comp_crc32c((crc), (data), (len)))
  #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
  
  extern pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len);
  extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
  extern pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len);
  
  #else
  /*
   * Use slicing-by-8 algorithm.
   *
   * On big-endian systems, the intermediate value is kept in reverse byte
   * order, to avoid byte-swapping during the calculation. FIN_CRC32C reverses
   * the bytes to the final order.
   */
  #define COMP_CRC32C(crc, data, len) \
  	((crc) = pg_comp_crc32c_sb8((crc), (data), (len)))
  #ifdef WORDS_BIGENDIAN
  #define FIN_CRC32C(crc) ((crc) = BSWAP32(crc) ^ 0xFFFFFFFF)
  #else
  #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
  #endif
  
  extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
  
  #endif
  
  #endif   /* PG_CRC32C_H */
  