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><A
NAME="FUNCTIONS-BITSTRING"
>9.6. Bit String Functions and Operators</A
></H1
><P
> This section describes functions and operators for examining and
manipulating bit strings, that is values of the types
<TT
CLASS="TYPE"
>bit</TT
> and <TT
CLASS="TYPE"
>bit varying</TT
>. Aside from the
usual comparison operators, the operators
shown in <A
HREF="functions-bitstring.html#FUNCTIONS-BIT-STRING-OP-TABLE"
>Table 9-11</A
> can be used.
Bit string operands of <TT
CLASS="LITERAL"
>&</TT
>, <TT
CLASS="LITERAL"
>|</TT
>,
and <TT
CLASS="LITERAL"
>#</TT
> must be of equal length. When bit
shifting, the original length of the string is preserved, as shown
in the examples.
</P
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-BIT-STRING-OP-TABLE"
></A
><P
><B
>Table 9-11. Bit String Operators</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Operator</TH
><TH
>Description</TH
><TH
>Example</TH
><TH
>Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
> <TT
CLASS="LITERAL"
>||</TT
> </TD
><TD
>concatenation</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' || B'011'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>10001011</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>&</TT
> </TD
><TD
>bitwise AND</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' & B'01101'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>00001</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>|</TT
> </TD
><TD
>bitwise OR</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' | B'01101'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>11101</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>#</TT
> </TD
><TD
>bitwise XOR</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' # B'01101'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>11100</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>~</TT
> </TD
><TD
>bitwise NOT</TD
><TD
><TT
CLASS="LITERAL"
>~ B'10001'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>01110</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
><<</TT
> </TD
><TD
>bitwise shift left</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' << 3</TT
></TD
><TD
><TT
CLASS="LITERAL"
>01000</TT
></TD
></TR
><TR
><TD
> <TT
CLASS="LITERAL"
>>></TT
> </TD
><TD
>bitwise shift right</TD
><TD
><TT
CLASS="LITERAL"
>B'10001' >> 2</TT
></TD
><TD
><TT
CLASS="LITERAL"
>00100</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><P
> The following <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>-standard functions work on bit
strings as well as character strings:
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>length</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>bit_length</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>octet_length</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>position</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>substring</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>overlay</CODE
></TT
>.
</P
><P
> The following functions work on bit strings as well as binary
strings:
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>get_bit</CODE
></TT
>,
<TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>set_bit</CODE
></TT
>.
When working with a bit string, these functions number the first
(leftmost) bit of the string as bit 0.
</P
><P
> In addition, it is possible to cast integral values to and from type
<TT
CLASS="TYPE"
>bit</TT
>.
Some examples:
</P><PRE
CLASS="PROGRAMLISTING"
>44::bit(10) <I
CLASS="LINEANNOTATION"
>0000101100</I
>
44::bit(3) <I
CLASS="LINEANNOTATION"
>100</I
>
cast(-44 as bit(12)) <I
CLASS="LINEANNOTATION"
>111111010100</I
>
'1110'::bit(4)::integer <I
CLASS="LINEANNOTATION"
>14</I
></PRE
><P>
Note that casting to just <SPAN
CLASS="QUOTE"
>"bit"</SPAN
> means casting to
<TT
CLASS="LITERAL"
>bit(1)</TT
>, and so will deliver only the least significant
bit of the integer.
</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
> Prior to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 8.0, casting an
integer to <TT
CLASS="TYPE"
>bit(n)</TT
> would copy the leftmost <TT
CLASS="LITERAL"
>n</TT
>
bits of the integer, whereas now it copies the rightmost <TT
CLASS="LITERAL"
>n</TT
>
bits. Also, casting an integer to a bit string width wider than
the integer itself will sign-extend on the left.
</P
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