bit 函数和操作符

MySQL

&Bitwise AND
<<Left shift
>>Shift right
BIT_COUNTReturns the number of set bits
^Bitwise XOR
|Bitwise OR
~Bitwise NOT

PostgreSQL

PostgreSQL bit_count

需要自定义, 写两个C函数来解决

> vi bit_count.c
#include "postgres.h"
#include "fmgr.h"
#include "utils/varbit.h"
PG_MODULE_MAGIC;PG_FUNCTION_INFO_V1(bit_count1);
PG_FUNCTION_INFO_V1(bit_count2);Datum
bit_count1(PG_FUNCTION_ARGS)
{VarBit     *arg = PG_GETARG_VARBIT_P(0);uint32          mask;bits8      *r;int                     nbits = 0;/* Check that the bit string is not too long */if (VARBITLEN(arg) > 32)ereport(ERROR,(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),errmsg("integer out of range")));mask = 0;for (r = VARBITS(arg); r < VARBITEND(arg); r++){mask <<= BITS_PER_BYTE;mask |= *r;}/* Now shift the mask to take account of the padding at the end */mask >>= VARBITPAD(arg);/* this code relies on mask being an unsigned type */while (mask){if (mask & 1)nbits++;mask >>= 1;}PG_RETURN_INT32(nbits);
}Datum
bit_count2(PG_FUNCTION_ARGS)
{uint32          mask = PG_GETARG_INT32(0);int                     nbits = 0;while (mask){if (mask & 1)nbits++;mask >>= 1;}PG_RETURN_INT32(nbits);
}> gcc -O3 -Wall -Wextra -Werror -I /home/digoal/postgresql-9.5.0/src/include -g -fPIC -c ./bit_count.c -o bit_count.o
> gcc -O3 -Wall -Wextra -Werror -I /home/digoal/postgresql-9.5.0/src/include -g -shared bit_count.o -o libbit_count.so
> cp libbit_count.so /home/digoal/pgsql9.5/lib/
> psql
postgres=# create or replace function bit_count(varbit) returns int as '$libdir/libbit_count.so', 'bit_count1' language c strict ;
CREATE FUNCTION
postgres=# create or replace function bit_count(int) returns int as '$libdir/libbit_count.so', 'bit_count2' language c strict ;
CREATE FUNCTION
postgres=# select bit_count(bit'1111');bit_count
-----------4
(1 row)
postgres=# select bit_count(bit'1111011001');bit_count
-----------7
(1 row)postgres=# select bit_count(99);bit_count
-----------4
(1 row)postgres=# select bit_count(10);bit_count
-----------2
(1 row)

PostgreSQL还支持set_bit

set_bit
postgres=#  select set_bit(bit'11111',1,0);set_bit
---------10111
(1 row)
postgres=#  select set_bit(bit'11111',0,0);set_bit
---------01111
(1 row)