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 Section Comparison Operators, as well as the operators shown below.

Bit String Operators

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

Bit String Functions

Some of the functions available for binary strings are also available for bit strings, as shown below.

bit_count

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_length ( bit ) → integer

Returns number of bits in the bit string.

bit_length(B'10111') → 5

length

length ( bit ) → integer

Returns number of bits in the bit string.

length(B'10111') → 5

octet_length

octet_length ( bit ) → integer

Returns number of bytes in the bit string.

octet_length(B'1011111011') → 2

overlay

overlay ( bitsbit PLACINGnewsubstringbit FROMstartinteger [ FORcount 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

position ( substringbit INbits 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

substring ( bitsbit [ FROMstartinteger ] [ FORcount integer ] ) → bit

Extracts the substring of битовой_строки 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

get_bit ( bitsbit,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

set_bit ( bitsbit,ninteger,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

Notes

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.