String Instructions

The following instruction groups LODS, STOS, and MOVS are string functions, which are discussed shortly. An extra instruction REP is used to repeatedly execute a list of data types for a count indicated by the looping count register (CX/ECX/RCX). The register is dependent upon the data-bit mode (16/32/64-bit).

There are additional string instructions not discussed in this chapter. CMPS and SCAS are discussed in Chapter 9, "Comparison." The INS and OUTS instructions are discussed in Chapter 17, "PC I/O." These should be used very carefully . There are alternatives that use register pairing and other methods of optimization. With older processors these were the optimal method of data manipulation but with the newer processors that is not so much the case any more. Loop counters need to be large values to be effective.

Table 3-13: String function and associated index register(s)

Mnemonic

ESI

EDI

CMPSx