Chapter 8 operation bit and bit string (4)

Chapter viii. Operation bits and bit strings （ Four ）

Operate on a bit string implemented as an integer

Set bit

To create a new bit string stored as an integer , Please sum each bit 2 The power of ：

set bitint = (2**2) + (2**5) + (2**10)
 
write bitint
1060

To set the bits in an existing bit string to 1, Please use $zboolean function （ Logic OR） The option to 7(arg1 ! arg2)：

set bitint = $zboolean(bitint, 2**4, 7)

write bitint
1076

To set the bits in an existing bit string to 0, Please use $zboolean Options for functions 2(arg1 & ~arg2)：

set bitint = $zboolean(bitint, 2**4, 2)

write bitint
1060

To switch bits in an existing bit string , Please use $zboolean function （ Logic XOR） The option to 6(arg1 ^ arg2)：

set bitint = $zboolean(bitint, 2**4, 6)

write bitint
1076
set bitint = $zboolean(bitint, 2**4, 6)

write bitint
1060

Test whether the bit is set

To display a bit string as an integer , You can use the following methods , This method loops the bits and uses $zboolean function ：

Class Util.BitUtil Extends %RegisteredObject
{
    

/// w ##class(Util.BitUtil).LogicalToDisplay(1)
ClassMethod LogicalToDisplay(bitint As %Integer)
{
    
	s str = ""
	for i = 0 : 1 {
     
		q:((2 ** i) > bitint)
		if $zboolean(bitint, 2 ** i, 1) {
    
			s str = str _ 1
		} else {
    
			s str = str _ 0
		}
	}
	q str
}

}

DHC-APP>w ##class(Util.BitUtil).LogicalToDisplay(101000)
00010001010100011

Find the setting bit

This method uses $Zlog The bit string() function sets which bits in a bit string are integers , This function returns with 10 The value of the base . This method deletes smaller and smaller bit string blocks , Until there is nothing left ：

/// w ##class(Util.BitUtil).FindSetBits(2)
ClassMethod FindSetBits(bitint As %Integer)
{
    
	s bits = "" 
	while (bitint '= 0) {
     
		s bit = $zlog(bitint) \ $zlog(2)
		s bits = bit _ " " _ bits
		s bitint = bitint - (2 ** bit) 
	} 
	q bits
}

DHC-APP>w ##class(Util.BitUtil).FindSetBits(3)
0 1

Perform bitwise arithmetic

Use $zboolean Function performs bitwise logical operations on a bit string stored as an integer .

For this example , Suppose there are two bit strings a and b, Store as an integer , And one. LogicalToDisplay() Method , Such as Display Bits As defined in , Used to display these bits .

do ##class(User.BitInt).LogicalToDisplay(a)
100110111
do ##class(User.BitInt).LogicalToDisplay(b)
001000101

Use $zboolean Options for functions 7 Bitwise execution logic OR：

set c = $zboolean(a, b, 7)

do ##class(User.BitInt).LogicalToDisplay(c)
101110111

Use $zboolean Options for functions 1 Execute logic and... In place ：

set d = $zboolean(a, b, 1)

do ##class(User.BitInt).LogicalToDisplay(d)
000000101

Convert to regular bit string

To convert a bit string stored as an integer to a regular bit string , Please use $factor function . For this example , Suppose there is a string of bits that is an integer bitint And a FindSetBits() Method , Such as Find Set Bits As defined in , To show which bits are set .

do ##class(User.BitInt).FindSetBits(bitint)
2 5 10
set bitstring = $factor(bitint)

zwrite bitstring 
bitstring=$zwc(128,4)_$c(36,4,0,0)/*$bit(3,6,11)*/

Please note that , The bits in the regular bit string seem to have shifted one bit to the right , Because the bit string has no bits 0. The first bit in the bit string is bit 1.