9.17 The bitwise negation operator
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C-- lets you quickly specify bitwise negation of the value of a memory
variable or register, by putting '!' in front of it and ';' after it. This
is equivalent to the assembler command 'NOT'. All 0's become 1's and all
1's become 0's.
A few examples:
!AX; // same as 'AX ^ = OxFFFF;' but quicker
!node; // changes the value of 'node' to its logical inverse
!CL; // same as 'CL ^ = OxFF;' but quicker