Rep instruction x86

All CPU instructions are 100% functional to reach compatibility with older CPUs. So why to avoid some instruction? There is no realy deprecated x86 EDIT: added simple speed test to check strings instruction rep cmp on different versions of CPUs. Test is made under Delphi IDE but the asm part is Further clarified the use of the REP instruction as filler in "Code Padding Using Neutral Code Fillers" on. by decoding and executing the x86 instructions using a proprietary microarchitecture. This microarchitecture allows the delivery of maximum performance when running x86-based PC software. The full x86 instruction set is large and complex (Intel's x86 instruction set manuals comprise over 2900 pages), and we do not cover it all in this guide. In this guide, we will limit our attention to more modern aspects of x86 programming, and delve into the instruction set only in enough detail to get a Instructions Instructions are the building blocks of assembly programs. In x86 assembly Instructions has two components: Mnemonic and operands. Rep instructions are used to manipulate data buffers. They are also called string instructions and usually in the form of an array of bytes but they • Data Transfer Instructions • Control Flow Instructions • Arithmetic Instructions • Logic Instructions • Shift section .code ; copy mystr into mystr2 mov esi, mystr mov edi, mystr2 cld rep movsw ; due x86 instructions can be anywhere between 1 and 15 bytes long. The length is defined separately for 4. Instruction tables: Lists of instruction latencies, throughputs and micro-operation breakdowns for Intel, AMD, and VIA CPUs. The figures in the instruction tables represent the results of my measurements rather than the offi-cial values published by microprocessor vendors. For example, a fairly powerful x86 instruction is the repeat. move instruction (rep movs), which copies C bytes of data. Implementations of the x86 ISA break up the repeat move instruction into smaller operations, or micro-ops, that indi-vidually perform the required operations of loading the data x86 Instruction Set Architecture. Table 4-1: Logical Processor State After Removal of Reset. Register or Resource. Chapter 6: Instruction Set Expansion. small numbers; at other times, with substantial additions to the instruction rep-ertoire (e.g., MMX and SSE). For x86 CPUs, individual instructions in a program can be much more involved than what you might consider as a single operation. For example, the instruction rep movs implements memcpy(edi, esi, ecx) (i.e. it copies a variable amount of memory from one place to another). x86 Instruction Data Structure: The length of any instruction must not exceed 15-bytes, or the processor will trigger an exception. As new models of the x86 family are released, the instruction set is extended with new features. Here we provide a chronologically ordered summary of what was 0. Introduction. The x86 instruction set architecture is at the heart of CPUs that power our home computers and remote servers for over two decades. These string instructions and the rep prefixes bring some iterated compound operations into assembly language. They represent some of the