This command allows the user to specify the desired form of a numeric constant. Please note that some constants have a fixed form and can not be modified. This mainly includes constants generated by the decompiler on the fly.
The decompiler ties the number format information to the instruction that generated the constant. The instruction address and the operand number are used for that. If a constant, which was generated by a single instruction, is used in many different locations in the pseudocode, all these locations will be modified at once.
Using the 'invert sign' negates the constant and resets the enum/char flag if it was set.
When this command is applied the first time to a negative constant, the output will seemingly stay the same. However, the list of symbolic constants available to the M hotkey changes. For example, if the constant is '-2', then before inverting the sign the symbolic constants corresponding to '-2' are available. After inverting the sign the symbolic constants corresponding to '2' are available.
The T hotkey applies the structure offset to the number. For positive numbers, it usually converts the number into offsetof() macro. For negative numbers, it usually converts the whole (var-num) expression into the CONTAINING_RECORD macro. By the way, the decompiler tries to use other hints to detect this macro. It checks if the number corresponds to a structure offset in the disassembly listing. For example, an expression like
v1 = (structype *)((char *)v2 - num);
can be converted into
v1 = CONTAINING_RECORD(v2, structype, fieldname);
where structype * is the type of v1 and offsetof(structype, fieldname) == num. Please note that v2 must be declared as a pointer to the corresponding structure field, otherwise the conversion may fail.