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Which flag is set when the result is zero?
Along with a carry flag, a sign flag and an overflow flag, the zero flag is used to check the result of an arithmetic operation, including bitwise logical instructions. It is set to 1, or true, if an arithmetic result is zero, and reset otherwise.
What is the purpose of zero flag?
7.1.1 The Zero Flag The purpose of the zero flag is to indicate whether the execution of the last instruction that affects the zero flag has produced a zero result. If the result is zero, ZF = 1; otherwise, ZF = 0.
How is the negative flag set?
The negative flag is set according to the result in the x86 series processors by the following instructions (referring to the Intel 80386 manual): All arithmetic operations except multiplication and division; compare instructions (equivalent to subtract instructions without storing the result);
Which flag is set when the result is positive or negative?
Sign Flag (SF) – set to 1 when result is negative. When result is positive it is set to 0. Actually this flag take the value of the most significant bit. Overflow Flag (OF) – set to 1 when there is a signed overflow.
When to use the zero, overflow and sign flags?
According to my book: For signed integers, there are three flags that are important: the zero (ZF) flag, the overflow (OF) flag and the sign (SF) flag. The overflow flag is set if the result of an operation overflows (or underflows). The sign flag is set if the result of an operation is negative.
When to use the sign flag in a conditional jump?
The sign flag is also used in the JG (jump if greater-than), JNG (jump if not greater-than) and similar conditional jump instructions. Set if the result of the instruction has gone beyond the limit of the data size (ie. a “carry” has occurred). For example suppose in an 8 bit instruction the value of 1 is added to 255.
How is the desciption of the sign flag set?
The desciption of the sign flag in Intel’s manual is “Set equal to the most-significant bit of the result, which is the sign bit of a signed integer. (0 indicates a positive value and 1 indicates a negative value.)”.
When do you set the C flag to zero?
Mathematically, 0xFF + 0x01 = 0x100, but 256 doesn’t fit in an 8-bit register, so the C flag gets set, and the bit pattern 0b00000000 is stored in A. Often time, manuals will say something like “The Z flag is set if the result is zero” but that seems hopelessly ambiguous to mean.