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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 || bitbit

Concatenation

B'10001' || B'011'10001011

bit & bitbit

Bitwise AND (inputs must be of equal length)

B'10001' & B'01101'00001

bit | bitbit

Bitwise OR (inputs must be of equal length)

B'10001' | B'01101'11101

bit # bitbit

Bitwise exclusive OR (inputs must be of equal length)

B'10001' # B'01101'11100

~ bitbit

Bitwise NOT

~ B'10001'01110

bit << integerbit

Bitwise shift left (string length is preserved)

B'10001' << 301000

bit >> integerbit

Bitwise shift right (string length is preserved)

B'10001' >> 200100


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_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 starting index of 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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