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A subtract with borrow (SBB) instruction will compute a−b−C = a−(b+C), while a subtract without borrow (SUB) acts as if the borrow bit were clear. The 6800 , 680x0 , 8051 , 8080 / Z80 , and x86 [ 2 ] families (among others) use a borrow bit.
subtraction when D = 1. This works because when D = 1 the A input to the adder is really A and the carry in is 1. Adding B to A and 1 yields the desired subtraction of B − A. A way you can mark number A as positive or negative without using a multiplexer on each bit is to use an XOR gate to precede each bit instead.
(This makes the subtract immediate instruction redundant, as it is equivalent to an add of the negative.) The move-to-accumulator and clear instructions do not modify any flags. In addition to the zero, carry, and digit carry flags (called AC by Holtek), there an overflow flag which is set by the same add and subtract instructions which set AC.
x86 assembly language is a family of low-level programming languages that are used to produce ... subtraction, negation, multiplication, division, remainder, square ...
In computer programming, assembly language (alternatively assembler language [1] or symbolic machine code), [2] [3] [4] often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence between the instructions in the language and the architecture's machine code instructions. [5]
In arithmetic operations (e.g., addition, subtraction), the algorithm starts by invoking an ALU operation on the operands' LS fragments, thereby producing both a LS partial and a carry out bit. The algorithm writes the partial to designated storage, whereas the processor's state machine typically stores the carry out bit to an ALU status register.
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
The subleq instruction ("subtract and branch if less than or equal to zero") subtracts the contents at address a from the contents at address b, stores the result at address b, and then, if the result is not positive, transfers control to address c (if the result is positive, execution proceeds to the next instruction in sequence).