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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode LODS</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="LOCK.htm"> LOCK Assert LOCK# Signal Prefix</A><BR><B>next:</B><A HREF="LOOP.htm"> LOOP/LOOPcond Loop Control with CX Counter</A><P><HR><P><H1>LODS/LODSB/LODSW/LODSD -- Load String Operand</H1><PRE>Opcode Instruction Clocks DescriptionAC LODS m8 5 Load byte [(E)SI] into ALAD LODS m16 5 Load word [(E)SI] into AXAD LODS m32 5 Load dword [(E)SI] into EAXAC LODSB 5 Load byte DS:[(E)SI] into ALAD LODSW 5 Load word DS:[(E)SI] into AXAD LODSD 5 Load dword DS:[(E)SI] into EAX</PRE><H2>Operation</H2><PRE>IF AddressSize = 16THEN use SI for source-indexELSE (* AddressSize = 32 *) use ESI for source-index;FI;IF byte type of instructionTHEN AL := [source-index]; (* byte load *) IF DF = 0 THEN IncDec := 1 ELSE IncDec := -1; FI;ELSE IF OperandSize = 16 THEN AX := [source-index]; (* word load *) IF DF = 0 THEN IncDec := 2 ELSE IncDec := -2; FI; ELSE (* OperandSize = 32 *) EAX := [source-index]; (* dword load *) IF DF = 0 THEN IncDec := 4 ELSE IncDec := -4; FI; FI;FI;source-index := source-index + IncDec</PRE><H2>Description</H2>LODS loads the AL, AX, or EAX register with the memory byte, word,or doubleword at the location pointed to by the source-index register.After the transfer is made, the source-index register is automaticallyadvanced. If the direction flag is 0 (<A HREF="CLD.htm">CLD</A> was executed), the source indexincrements; if the direction flag is 1 (<A HREF="STD.htm">STD</A> was executed), it decrements.The increment or decrement is 1 if a byte is loaded, 2 if a word is loaded,or 4 if a doubleword is loaded.<P>If the address-size attribute for this instruction is 16 bits, SI is usedfor the source-index register; otherwise the address-size attribute is 32bits, and the ESI register is used. The address of the source data isdetermined solely by the contents of ESI/SI. Load the correct index valueinto SI before executing the LODS instruction. LODSB, LODSW, LODSD aresynonyms for the byte, word, and doubleword LODS instructions.<P>LODS can be preceded by the <A HREF="REP.htm">REP</A> prefix; however, LODS is used more typicallywithin a <A HREF="LOOP.htm">LOOP</A> construct, because further processing of the data moved intoEAX, AX, or AL is usually necessary.<H2>Flags Affected</H2>None<H2>Protected Mode Exceptions</H2>#GP(0) for an illegal memory operand effective address in the CS, DS,ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment;#PF(fault-code) for a page fault<H2>Real Address Mode Exceptions</H2>Interrupt 13 if any part of the operand would lie outside of the effectiveaddress space from 0 to 0FFFFH<H2>Virtual 8086 Mode Exceptions</H2>Same exceptions as in Real Address Mode; #PF(fault-code) for a pagefault<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="LOCK.htm"> LOCK Assert LOCK# Signal Prefix</A><BR><B>next:</B><A HREF="LOOP.htm"> LOOP/LOOPcond Loop Control with CX Counter</A></BODY>⌨️ 快捷键说明
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