?? cmps.htm
字號:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><HTML><HEAD><TITLE>80386 Programmer's Reference Manual -- Opcode CMPS</TITLE></HEAD><BODY><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="CMP.htm"> CMP Compare Two Operands</A><BR><B>next:</B><A HREF="CWD.htm"> CWD/CDQ Convert Word to Doubleword/Convert Doubleword to Quadword</A><P><HR><P><H1>CMPS/CMPSB/CMPSW/CMPSD -- Compare String Operands</H1><PRE>Opcode Instruction Clocks DescriptionA6 CMPS m8,m8 10 Compare bytes ES:[(E)DI] (second operand) with [(E)SI] (first operand)A7 CMPS m16,m16 10 Compare words ES:[(E)DI] (second operand) with [(E)SI] (first operand)A7 CMPS m32,m32 10 Compare dwords ES:[(E)DI] (second operand) with [(E)SI] (first operand)A6 CMPSB 10 Compare bytes ES:[(E)DI] with DS:[SI]A7 CMPSW 10 Compare words ES:[(E)DI] with DS:[SI]A7 CMPSD 10 Compare dwords ES:[(E)DI] with DS:[SI]</PRE><H2>Operation</H2><PRE>IF (instruction = CMPSD) OR (instruction has operands of type DWORD)THEN OperandSize := 32;ELSE OperandSize := 16;FI;IF AddressSize = 16THEN use SI for source-index and DI for destination-indexELSE (* AddressSize = 32 *) use ESI for source-index and EDI for destination-index;FI;IF byte type of instructionTHEN [source-index] - [destination-index]; (* byte comparison *) IF DF = 0 THEN IncDec := 1 ELSE IncDec := -1; FI;ELSE IF OperandSize = 16 THEN [source-index] - [destination-index]; (* word comparison *) IF DF = 0 THEN IncDec := 2 ELSE IncDec := -2; FI; ELSE (* OperandSize = 32 *) [source-index] - [destination-index]; (* dword comparison *) IF DF = 0 THEN IncDec := 4 ELSE IncDec := -4; FI; FI;FI;source-index := source-index + IncDec;destination-index := destination-index + IncDec;</PRE><H2>Description</H2>CMPS compares the byte, word, or doubleword pointed to by the source-indexregister with the byte, word, or doubleword pointed to by thedestination-index register.<P>If the address-size attribute of this instruction is 16 bits, SI and DIwill be used for source- and destination-index registers; otherwise ESI andEDI will be used. Load the correct index values into SI and DI (or ESI andEDI) before executing CMPS.<P>The comparison is done by subtracting the operand indexed bythe destination-index register from the operand indexed by the source-indexregister.<P>Note that the direction of subtraction for CMPS is [SI] - [DI] or[ESI] - [EDI]. The left operand (SI or ESI) is the source and the rightoperand (DI or EDI) is the destination. This is the reverse of the usualIntel convention in which the left operand is the destination and the rightoperand is the source.<P>The result of the subtraction is not stored; only the flags reflect thechange. The types of the operands determine whether bytes, words, ordoublewords are compared. For the first operand (SI or ESI), the DS registeris used, unless a segment override byte is present. The second operand (DIor EDI) must be addressable from the ES register; no segment override ispossible.<P>After the comparison is made, both the source-index register anddestination-index register are automatically advanced. If the direction flagis 0 (<A HREF="CLD.htm">CLD</A> was executed), the registers increment; if the direction flag is 1(<A HREF="STD.htm">STD</A> was executed), the registers decrement. The registers increment ordecrement by 1 if a byte is compared, by 2 if a word is compared, or by 4 ifa doubleword is compared.<P>CMPSB, CMPSW and CMPSD are synonyms for the byte, word, anddoubleword CMPS instructions, respectively.<P>CMPS can be preceded by the <A HREF="REP.htm">REPE</A> or <A HREF="REP.htm">REPNE</A> prefix for block comparison of CXor ECX bytes, words, or doublewords. Refer to the description of the <A HREF="REP.htm">REP</A>instruction for more information on this operation.<H2>Flags Affected</H2>OF, SF, ZF, AF, PF, and CF as described in <A HREF="appc.htm">Appendix C</A><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 page fault<P><HR><P><B>up:</B> <A HREF="c17.htm">Chapter 17 -- 80386 Instruction Set</A><BR><B>prev:</B><A HREF="CMP.htm"> CMP Compare Two Operands</A><BR><B>next:</B><A HREF="CWD.htm"> CWD/CDQ Convert Word to Doubleword/Convert Doubleword to Quadword</A></BODY>?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -