9.6. Bit String Functions and Operators
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## 9.6. Bit String Functions and Operators #

This section describes functions and operators for examining and manipulating bit strings, that is values of the types bit and bit varying. (While only type bit is mentioned in these tables, values of type bit varying can be used interchangeably.) Bit strings support the usual comparison operators shown in Table 9.1, as well as the operators shown in Table 9.14.

Table 9.14. Bit String Operators

Operator Description Example(s)
bit `||` bit bit Concatenation `B'10001' || B'011'` 10001011
bit `&` bit bit Bitwise AND (inputs must be of equal length) `B'10001' & B'01101'` 00001
bit `|` bit bit Bitwise OR (inputs must be of equal length) `B'10001' | B'01101'` 11101
bit `#` bit bit Bitwise exclusive OR (inputs must be of equal length) `B'10001' # B'01101'` 11100
`~` bit bit Bitwise NOT `~ B'10001'` 01110
bit `<<` integer bit Bitwise shift left (string length is preserved) `B'10001' << 3` 01000
bit `>>` integer bit Bitwise shift right (string length is preserved) `B'10001' >> 2` 00100

Some of the functions available for binary strings are also available for bit strings, as shown in Table 9.15.

Table 9.15. Bit String Functions

Function Description Example(s)
`bit_count` ( bit ) bigint Returns the number of bits set in the bit string (also known as “popcount”). `bit_count(B'10111')` 4
`bit_length` ( bit ) integer Returns number of bits in the bit string. `bit_length(B'10111')` 5
`length` ( bit ) integer Returns number of bits in the bit string. `length(B'10111')` 5
`octet_length` ( bit ) integer Returns number of bytes in the bit string. `octet_length(B'1011111011')` 2
`overlay` ( `bits` bit `PLACING` `newsubstring` bit `FROM` `start` integer [ `FOR` `count` integer ] ) bit Replaces the substring of `bits` that starts at the `start`'th bit and extends for `count` bits with `newsubstring`. If `count` is omitted, it defaults to the length of `newsubstring`. `overlay(B'01010101010101010' placing B'11111' from 2 for 3)` 0111110101010101010
`position` ( `substring` bit `IN` `bits` bit ) integer Returns first starting index of the specified `substring` within `bits`, or zero if it's not present. `position(B'010' in B'000001101011')` 8
`substring` ( `bits` bit [ `FROM` `start` integer ] [ `FOR` `count` integer ] ) bit Extracts the substring of `bits` starting at the `start`'th bit if that is specified, and stopping after `count` bits if that is specified. Provide at least one of `start` and `count`. `substring(B'110010111111' from 3 for 2)` 00
`get_bit` ( `bits` bit, `n` integer ) integer Extracts `n`'th bit from bit string; the first (leftmost) bit is bit 0. `get_bit(B'101010101010101010', 6)` 1
`set_bit` ( `bits` bit, `n` integer, `newvalue` integer ) bit Sets `n`'th bit in bit string to `newvalue`; the first (leftmost) bit is bit 0. `set_bit(B'101010101010101010', 6, 0)` 101010001010101010

In addition, it is possible to cast integral values to and from type bit. Casting an integer to bit(n) copies the rightmost `n` bits. Casting an integer to a bit string width wider than the integer itself will sign-extend on the left. Some examples:

    44::bit(10)                    0000101100
    44::bit(3)                     100
    cast(-44 as bit(12))           111111010100
    '1110'::bit(4)::integer        14

Note that casting to just “bit” means casting to `bit(1)`, and so will deliver only the least significant bit of the integer.

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