instruction-set

What is the difference between MOV and LEA?

由 雨燕双飞 提交于 2019-11-26 11:35:33
I would like to know what the difference between these instructions is: MOV AX, [TABLE-ADDR] and LEA AX, [TABLE-ADDR] Ruben Bartelink LEA means Load Effective Address MOV means Load Value In short, LEA loads a pointer to the item you're addressing whereas MOV loads the actual value at that address. The purpose of LEA is to allow one to perform a non-trivial address calculation and store the result [for later usage] LEA ax, [BP+SI+5] ; Compute address of value MOV ax, [BP+SI+5] ; Load value at that address Where there are just constants involved, MOV (through the assembler's constant

Which arithmetic operations are the same on unsigned and two's complement signed numbers?

由 末鹿安然 提交于 2019-11-26 04:56:31
问题 I\'m designing a simple toy instruction set and accompanying emulator, and I\'m trying to figure out what instructions to support. In the way of arithmetic, I currently have unsigned add, subtract, multiply, and divide. However, I can\'t seem to find a definitive answer to the following question: Which of the arithmetic operators need signed versions, and for which are the unsigned and two\'s complement signed versions equivalent? So, for example, 1111 in two\'s complement is equal to -1. If

Difference between movq and movabsq in x86-64

由 陌路散爱 提交于 2019-11-26 04:54:39
问题 I\'m a newcomer here and just starting to study assembly language. So please correct me if I\'m wrong, or if this post doesn\'t make any sense I will delete. I\'m talking about data movement instructions in the x86-64 Intel architecture. I have read that the regular movq instruction can only have immediate source operands that can be represented as 32-bit two\'s complement numbers, while the movabsq instruction can have an arbitrary 64-bit immediate value as its source operand and can only
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