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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode REP</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="RCL.htm"> RCL/RCR/ROL/ROR Rotate</A><BR><B>next:</B><A HREF="RET.htm"> RET Return from Procedure</A><P><HR><P><H1>REP/REPE/REPZ/REPNE/REPNZ -- Repeat Following String Operation</H1><PRE>Opcode Instruction Clocks DescriptionF3 6C REP INS r/m8, DX 13+6*(E)CX, pm=7+6*(E)CXIf CPL <= IOPL/ 27+6*(E)CXIf CPL > IOPL or if in virtual 8086 mode Input (E)CX bytes from port DX into ES:[(E)DI]F3 6D REP INS r/m16,DX 13+6*(E)CX, pm=7+6*(E)CXIf CPL <= IOPL/ 27+6*(E)CXIf CPL > IOPL or if in virtual 8086 mode Input (E)CX words from port DX into ES:[(E)DI]F3 6D REP INS r/m32,DX 13+6*(E)CX, pm=7+6*(E)CXIf CPL <= IOPL/ 27+6*(E)CXIf CPL > IOPL or if in virtual 8086 mode Input (E)CX dwords from port DX into ES:[(E)DI]F3 A4 REP MOVS m8,m8 5+4*(E)CX Move (E)CX bytes from [(E)SI] to ES:[(E)DI]F3 A5 REP MOVS m16,m16 5+4*(E)CX Move (E)CX words from [(E)SI] to ES:[(E)DI]F3 A5 REP MOVS m32,m32 5+4*(E)CX Move (E)CX dwords from [(E)SI] to ES:[(E)DI]F3 6E REP OUTS DX,r/m8 5+12*(E)CX, pm=6+5*(E)CXIf CPL <= IOPL/ 26+5*(E)CXIf CPL > IOPL or if in virtual 8086 mode Output (E)CX bytes from [(E)SI] to port DXF3 6F REP OUTS DX,r/m16 5+12*(E)CX, pm=6+5*(E)CXIf CPL <= IOPL/ 26+5*(E)CXIf CPL > IOPL or if in virtual 8086 mode Output (E)CX words from [(E)SI] to port DXF3 6F REP OUTS DX,r/m32 5+12*(E)CX, pm=6+5*(E)CXIf CPL <= IOPL/ 26+5*(E)CXIf CPL > IOPL or if in virtual 8086 mode Output (E)CX dwords from [(E)SI] to port DXF3 AA REP STOS m8 5+5*(E)CX Fill (E)CX bytes at ES:[(E)DI] with ALF3 AB REP STOS m16 5+5*(E)CX Fill (E)CX words at ES:[(E)DI] with AXF3 AB REP STOS m32 5+5*(E)CX Fill (E)CX dwords at ES:[(E)DI] with EAXF3 A6 REPE CMPS m8,m8 5+9*N Find nonmatching bytes in ES:[(E)DI] and [(E)SI]F3 A7 REPE CMPS m16,m16 5+9*N Find nonmatching words in ES:[(E)DI] and [(E)SI]F3 A7 REPE CMPS m32,m32 5+9*N Find nonmatching dwords in ES:[(E)DI] and [(E)SI]F3 AE REPE SCAS m8 5+8*N Find non-AL byte starting at ES:[(E)DI]F3 AF REPE SCAS m16 5+8*N Find non-AX word starting at ES:[(E)DI]F3 AF REPE SCAS m32 5+8*N Find non-EAX dword starting at ES:[(E)DI]F2 A6 REPNE CMPS m8,m8 5+9*N Find matching bytes in ES:[(E)DI] and [(E)SI]F2 A7 REPNE CMPS m16,m16 5+9*N Find matching words in ES:[(E)DI] and [(E)SI]F2 A7 REPNE CMPS m32,m32 5+9*N Find matching dwords in ES:[(E)DI] and [(E)SI]F2 AE REPNE SCAS m8 5+8*N Find AL, starting at ES:[(E)DI]F2 AF REPNE SCAS m16 5+8*N Find AX, starting at ES:[(E)DI]F2 AF REPNE SCAS m32 5+8*N Find EAX, starting at ES:[(E)DI]</PRE><H2>Operation</H2><PRE>IF AddressSize = 16THEN use CX for CountReg;ELSE (* AddressSize = 32 *) use ECX for CountReg;FI;WHILE CountReg <> 0DO service pending interrupts (if any); perform primitive string instruction; CountReg := CountReg - 1; IF primitive operation is CMPB, CMPW, SCAB, or SCAW THEN IF (instruction is REP/REPE/REPZ) AND (ZF=1) THEN exit WHILE loop ELSE IF (instruction is REPNZ or REPNE) AND (ZF=0) THEN exit WHILE loop; FI; FI; FI;OD;</PRE><H2>Description</H2>REP, REPE (repeat while equal), and REPNE (repeat while not equal)are prefix that are applied to string operation. Each prefix cause thestring instruction that follows to be repeated the number of timesindicated in the count register or (for REPE and REPNE) until theindicated condition in the zero flag is no longer met.<P>Synonymous forms of REPE and REPNE are REPZ and REPNZ,respectively.<P>The REP prefixes apply only to one string instruction at a time. To repeata block of instructions, use the <A HREF="LOOP.htm">LOOP</A> instruction or another loopingconstruct.<P>The precise action for each iteration is as follows:<OL> <LI> If the address-size attribute is 16 bits, use CX for the count register; if the address-size attribute is 32 bits, use ECX for the count register. <LI> Check CX. If it is zero, exit the iteration, and move to the next instruction. <LI> Acknowledge any pending interrupts. <LI> Perform the string operation once. <LI> Decrement CX or ECX by one; no flags are modified. <LI> Check the zero flag if the string operation is <A HREF="SCAS.htm">SCAS</A> or <A HREF="CMPS.htm">CMPS</A>. If the repeat condition does not hold, exit the iteration and move to the next instruction. Exit the iteration if the prefix is REPE and ZF is 0 (the last comparison was not equal), or if the prefix is REPNE and ZF is one (the last comparison was equal). <LI> Return to step 1 for the next iteration.</OL>Repeated <A HREF="CMPS.htm">CMPS</A> and <A HREF="SCAS.htm">SCAS</A> instructions can be exited if the count isexhausted or if the zero flag fails the repeat condition. These two casescan be distinguished by using either the <A HREF="Jcc.htm">JCXZ</A> instruction, or by usingthe conditional jumps that test the zero flag (<A HREF="Jcc.htm">JZ</A>, <A HREF="Jcc.htm">JNZ</A>, and <A HREF="Jcc.htm">JNE</A>).<H2>Flags Affected</H2>ZF by REP <A HREF="CMPS.htm">CMPS</A> and REP <A HREF="SCAS.htm">SCAS</A> as described above<H2>Protected Mode Exceptions</H2>#UD if a repeat prefix is used before an instruction that is not in thelist above; further exceptions can be generated when the string operation isexecuted; refer to the descriptions of the string instructions themselves<H2>Real Address Mode Exceptions</H2>Interrupt 6 if a repeat prefix is used before an instruction that is not inthe list above; further exceptions can be generated when the stringoperation is executed; refer to the descriptions of the string instructionsthemselves<H2>Virtual 8086 Mode Exceptions</H2>#UD if a repeat prefix is used before an instruction that is not in thelist above; further exceptions can be generated when the string operation isexecuted; refer to the descriptions of the string instructions themselves<H2>Notes</H2>Not all input/output ports can handle the rate at which the REP <A HREF="INS.htm">INS</A>and REP <A HREF="OUTS.htm">OUTS</A> instructions execute.<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="RCL.htm"> RCL/RCR/ROL/ROR Rotate</A><BR><B>next:</B><A HREF="RET.htm"> RET Return from Procedure</A></BODY>⌨️ 快捷键说明
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