From b3005f3bce8c96191eb5e523ea2480766b496bd1 Mon Sep 17 00:00:00 2001 From: Peter Geoghegan Date: Mon, 29 Jun 2015 23:53:05 -0400 Subject: [PATCH 1/4] Add BSWAP64() byte-swapping macro This includes detection of __builtin_bswap64() built-in availability, which BSWAP64() often becomes no more than a simple wrapper for. BSWAP64() can be used to convert 64-bit big-endian unsigned integers to 64-bit little-endian unsigned integers, and vice-versa. Add another macro, ABBREV_STRING_UINT(), that allows string-like types to represent abbreviated keys as unsigned integers (ABBREV_STRING_UINT() will use BSWAP64() on 64-bit little-endian platforms). In future commits, certain types can be made to use simple 3-way unsigned integer comparisons (sizeof(Datum)-wide unsigned integers) within their abbreviated key comparators; they need only first use ABBREV_STRING_UINT() within their SortSupport conversion routines to alter the abbreviated representation and make this safe on all supported platforms. --- config/c-compiler.m4 | 18 ++++++++++++++ configure | 24 +++++++++++++++++++ configure.in | 1 + src/include/c.h | 22 +++++++++++++++++ src/include/pg_config.h.in | 3 +++ src/include/pg_config.h.win32 | 3 +++ src/include/port/pg_crc32c.h | 10 -------- src/include/utils/sortsupport.h | 52 +++++++++++++++++++++++++++++++++++++++++ 8 files changed, 123 insertions(+), 10 deletions(-) diff --git a/config/c-compiler.m4 b/config/c-compiler.m4 index 9feec0c..550d034 100644 --- a/config/c-compiler.m4 +++ b/config/c-compiler.m4 @@ -214,6 +214,24 @@ fi])# PGAC_C_BUILTIN_BSWAP32 +# PGAC_C_BUILTIN_BSWAP64 +# ------------------------- +# Check if the C compiler understands __builtin_bswap64(), +# and define HAVE__BUILTIN_BSWAP64 if so. +AC_DEFUN([PGAC_C_BUILTIN_BSWAP64], +[AC_CACHE_CHECK(for __builtin_bswap64, pgac_cv__builtin_bswap64, +[AC_COMPILE_IFELSE([AC_LANG_SOURCE( +[static unsigned long int x = __builtin_bswap64(0xaabbccddeeff0011);] +)], +[pgac_cv__builtin_bswap64=yes], +[pgac_cv__builtin_bswap64=no])]) +if test x"$pgac_cv__builtin_bswap64" = xyes ; then +AC_DEFINE(HAVE__BUILTIN_BSWAP64, 1, + [Define to 1 if your compiler understands __builtin_bswap64.]) +fi])# PGAC_C_BUILTIN_BSWAP64 + + + # PGAC_C_BUILTIN_CONSTANT_P # ------------------------- # Check if the C compiler understands __builtin_constant_p(), diff --git a/configure b/configure index 99ef10f..b771a83 100755 --- a/configure +++ b/configure @@ -11259,6 +11259,30 @@ if test x"$pgac_cv__builtin_bswap32" = xyes ; then $as_echo "#define HAVE__BUILTIN_BSWAP32 1" >>confdefs.h fi +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_bswap64" >&5 +$as_echo_n "checking for __builtin_bswap64... " >&6; } +if ${pgac_cv__builtin_bswap64+:} false; then : + $as_echo_n "(cached) " >&6 +else + cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ +static unsigned long int x = __builtin_bswap64(0xaabbccddeeff0011); + +_ACEOF +if ac_fn_c_try_compile "$LINENO"; then : + pgac_cv__builtin_bswap64=yes +else + pgac_cv__builtin_bswap64=no +fi +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext +fi +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__builtin_bswap64" >&5 +$as_echo "$pgac_cv__builtin_bswap64" >&6; } +if test x"$pgac_cv__builtin_bswap64" = xyes ; then + +$as_echo "#define HAVE__BUILTIN_BSWAP64 1" >>confdefs.h + +fi { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_constant_p" >&5 $as_echo_n "checking for __builtin_constant_p... " >&6; } if ${pgac_cv__builtin_constant_p+:} false; then : diff --git a/configure.in b/configure.in index 4143451..b5868b0 100644 --- a/configure.in +++ b/configure.in @@ -1317,6 +1317,7 @@ PGAC_C_FUNCNAME_SUPPORT PGAC_C_STATIC_ASSERT PGAC_C_TYPES_COMPATIBLE PGAC_C_BUILTIN_BSWAP32 +PGAC_C_BUILTIN_BSWAP64 PGAC_C_BUILTIN_CONSTANT_P PGAC_C_BUILTIN_UNREACHABLE PGAC_C_VA_ARGS diff --git a/src/include/c.h b/src/include/c.h index 8163b00..9be41dc 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -943,6 +943,28 @@ typedef NameData *Name; #define STATUS_FOUND (1) #define STATUS_WAITING (2) +/* byte swapping macros */ +#ifdef HAVE__BUILTIN_BSWAP32 +#define BSWAP32(x) __builtin_bswap32(x) +#else +#define BSWAP32(x) (((x << 24) & 0xff000000) | \ + ((x << 8) & 0x00ff0000) | \ + ((x >> 8) & 0x0000ff00) | \ + ((x >> 24) & 0x000000ff)) +#endif /* HAVE__BUILTIN_BSWAP32 */ + +#ifdef HAVE__BUILTIN_BSWAP64 +#define BSWAP64(x) __builtin_bswap64(x) +#else +#define BSWAP64(x) (((x << 56) & 0xff00000000000000UL) | \ + ((x << 40) & 0x00ff000000000000UL) | \ + ((x << 24) & 0x0000ff0000000000UL) | \ + ((x << 8) & 0x000000ff00000000UL) | \ + ((x >> 8) & 0x00000000ff000000UL) | \ + ((x >> 24) & 0x0000000000ff0000UL) | \ + ((x >> 40) & 0x000000000000ff00UL) | \ + ((x >> 56) & 0x00000000000000ffUL)) +#endif /* HAVE__BUILTIN_BSWAP64 */ /* * Append PG_USED_FOR_ASSERTS_ONLY to definitions of variables that are only diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in index dda73a8..a20e0cd 100644 --- a/src/include/pg_config.h.in +++ b/src/include/pg_config.h.in @@ -660,6 +660,9 @@ /* Define to 1 if your compiler understands __builtin_bswap32. */ #undef HAVE__BUILTIN_BSWAP32 +/* Define to 1 if your compiler understands __builtin_bswap64. */ +#undef HAVE__BUILTIN_BSWAP64 + /* Define to 1 if your compiler understands __builtin_constant_p. */ #undef HAVE__BUILTIN_CONSTANT_P diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32 index 6f7a773..8566065 100644 --- a/src/include/pg_config.h.win32 +++ b/src/include/pg_config.h.win32 @@ -508,6 +508,9 @@ /* Define to 1 if your compiler understands __builtin_bswap32. */ /* #undef HAVE__BUILTIN_BSWAP32 */ +/* Define to 1 if your compiler understands __builtin_bswap64. */ +/* #undef HAVE__BUILTIN_BSWAP64 */ + /* Define to 1 if your compiler understands __builtin_constant_p. */ /* #undef HAVE__BUILTIN_CONSTANT_P */ diff --git a/src/include/port/pg_crc32c.h b/src/include/port/pg_crc32c.h index c925c56..e5389aa 100644 --- a/src/include/port/pg_crc32c.h +++ b/src/include/port/pg_crc32c.h @@ -71,16 +71,6 @@ extern pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) #define COMP_CRC32C(crc, data, len) \ ((crc) = pg_comp_crc32c_sb8((crc), (data), (len))) #ifdef WORDS_BIGENDIAN - -#ifdef HAVE__BUILTIN_BSWAP32 -#define BSWAP32(x) __builtin_bswap32(x) -#else -#define BSWAP32(x) (((x << 24) & 0xff000000) | \ - ((x << 8) & 0x00ff0000) | \ - ((x >> 8) & 0x0000ff00) | \ - ((x >> 24) & 0x000000ff)) -#endif - #define FIN_CRC32C(crc) ((crc) = BSWAP32(crc) ^ 0xFFFFFFFF) #else #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF) diff --git a/src/include/utils/sortsupport.h b/src/include/utils/sortsupport.h index 4258630..a8bedfd 100644 --- a/src/include/utils/sortsupport.h +++ b/src/include/utils/sortsupport.h @@ -267,6 +267,58 @@ ApplySortAbbrevFullComparator(Datum datum1, bool isNull1, return compare; } +/* + * Make unsigned integer (Datum) 3-way comparisons safe for string-like types. + * + * For some types, their abbreviated representations could reasonably be built + * such that comparisons are binary string comparisons. For example, for a + * string type, an abbreviated comparator like this might be used: + * + * static int + * btstringcmp_abbrev(Datum x, Datum y, SortSupport ssup) + * { + * return memcmp((char *) &x, (char *) &y, sizeof(Datum)); + * } + * + * Perhaps the conversion routine packs NUL bytes used as sentinel values + * representing termination in the event of short strings too, so short strings + * require no special treatment (assuming NUL bytes are generally disallowed). + * There might be slightly different specifics for each type, but this basic + * pattern recurs relatively often. + * + * On big-endian machines, compilers might be able to optimize this to just a + * few CPU instructions (involving unsigned integer comparisons). Opclass + * authors should not rely on that, though. Instead, they should use the + * ABBREV_STRING_UINT() macro within their conversion routine to make sure that + * it's safe to use a 3-way comparator that performs simple unsigned integer + * comparisons explicitly. The abbreviated comparator should then look like + * this instead: + * + * static int + * btstringcmp_abbrev(Datum x, Datum y, SortSupport ssup) + * { + * if (x > y) + * return 1; + * else if (x == y) + * return 0; + * else + * return -1; + * } + * + * Apart from ensuring even cheaper comparisons on big-endian machines, this + * technique also works on little-endian machines, since a byteswap can be + * performed within ABBREV_STRING_UINT(). + */ +#ifdef WORDS_BIGENDIAN +#define ABBREV_STRING_UINT(x) (x) +#else /* !WORDS_BIGENDIAN */ +#if SIZEOF_DATUM == 8 +#define ABBREV_STRING_UINT(x) BSWAP64(x) +#else /* SIZEOF_DATUM != 8 */ +#define ABBREV_STRING_UINT(x) BSWAP32(x) +#endif /* SIZEOF_DATUM == 8 */ +#endif /* WORDS_BIGENDIAN */ + /* Other functions in utils/sort/sortsupport.c */ extern void PrepareSortSupportComparisonShim(Oid cmpFunc, SortSupport ssup); extern void PrepareSortSupportFromOrderingOp(Oid orderingOp, SortSupport ssup); -- 1.9.1