Negative flag
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In a computer processor the negative flag or sign flag is a single bit in a system status (flag) register used to indicate whether the result of the last mathematical operation produced a value in which the most significant bit (the left most bit) was set. In a two's complement interpretation of the result, the negative flag is set if the result was negative.
For example, in an 8-bit signed number system, -37 will be represented as 1101 1011 in binary (the most significant bit, or sign bit, is 1), while +37 will be represented as 0010 0101 (the most significant bit is 0).
The negative flag is set according to the result in the
Intel 80386 manual[1]
):
- All arithmetic operations except multiplication and division;
- compare instructions (equivalent to subtract instructions without storing the result);
- Logical instructions – XOR, AND, OR;
- TEST instructions (equivalent to AND instructions without storing the result).