9.6. Bit String Functions and Operators#
This section describes functions and operators for examining and manipulating bit strings, that is values of the typesbit andbit varying. (While only typebit is mentioned in these tables, values of typebit varying can be used interchangeably.) Bit strings support the usual comparison operators shown inTable 9.1, as well as the operators shown inTable 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 inTable 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 (bitsbitPLACINGnewsubstringbitFROMstartinteger [FORcountinteger] ) →bit
Replaces the substring ofbits that starts at thestart'th bit and extends forcount bits withnewsubstring. Ifcount is omitted, it defaults to the length ofnewsubstring. overlay(B'01010101010101010' placing B'11111' from 2 for 3) →0111110101010101010
|
position (substringbitINbitsbit ) →integer
Returns first starting index of the specifiedsubstring withinbits, or zero if it's not present. position(B'010' in B'000001101011') →8
|
substring (bitsbit [FROMstartinteger] [FORcountinteger] ) →bit
Extracts the substring ofbits starting at thestart'th bit if that is specified, and stopping aftercount bits if that is specified. Provide at least one ofstart andcount. substring(B'110010111111' from 3 for 2) →00
|
get_bit (bitsbit,ninteger ) →integer
Extractsn'th bit from bit string; the first (leftmost) bit is bit 0. get_bit(B'101010101010101010', 6) →1
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set_bit (bitsbit,ninteger,newvalueinteger ) →bit
Setsn'th bit in bit string tonewvalue; 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 typebit. Casting an integer tobit(n) copies the rightmostn 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)000010110044::bit(3)100cast(-44 as bit(12))111111010100'1110'::bit(4)::integer14
Note that casting to just“bit” means casting tobit(1), and so will deliver only the least significant bit of the integer.
