Question

[Assembly Language]Extended Subtraction Procedure.Create a procedure named Extended_Sub --(Receives: ESI and EDI point to the two integers, EBX points to a variable that will hold the result, and ECX indicates the size of operands (multiple of 32 bits). (Returns: nothing)It subtracts two binary integers of arbitrary size. The storage size of the two integers must be the same, and their size must be a multiple of 32 bits.Use the following data to test your program:.dataop1 QWORD 0A2B2A40674981234hop2 QWORD 08010870000234502hresult QWORD 1 DUP(0)

Answer 1

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Modern (i.e 386 and beyond) x86 processors have eight 32-bit general purpose registers, as depicted in Figure 1. The register names are mostly historical. For example, EAX used to be called the accumulator since it was used by a number of arithmetic operations, and ECX was known as the counter since it was used to hold a loop index. Whereas most of the registers have lost their special purposes in the modern instruction set, by convention, two are reserved for special purposes — the stack pointer (ESP) and the base pointer (EBP).

For the EAX, EBX, ECX, and EDX registers, subsections may be used. For example, the least significant 2 bytes of EAX can be treated as a 16-bit register called AX. The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH. These names refer to the same physical register. When a two-byte quantity is placed into DX, the update affects the value of DH, DL, and EDX. These sub-registers are mainly hold-overs from older, 16-bit versions of the instruction set. However, they are sometimes convenient when dealing with data that are smaller than 32-bits (e.g. 1-byte ASCII characters).

When referring to registers in assembly language, the names are not case-sensitive. For example, the names EAX and eax refer to the same register.

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