lecture3assemblylanguagefundamentals-資料下載頁(yè)
2024-09-29 20:50本頁(yè)面
【導(dǎo)讀】Intel-BasedComputers,SampleProgram. Assembling,Linking,andRunning. DefiningData. SymbolicConstants. IntegerConstants. IntegerExpressions. Examples. andanexponent.Aencodedreal(hex)showstheIEEE. Examples:. "A"or'A'"12345"isastring(5bytes). Identifiers. Maycontainletters,digits,"?","_","@",or"$". Caseinsensitive. Maxof247characters. Directives. formatted.Example:. Instructions. ordata.Instructions. Comments.COMMENT!SampleProgram. Assembling,Linking,andRunning. DefiningData. SymbolicConstants
【正文】 100 ? Similar to C++ code const int numValues = 25。 const int min = 5。 const int max = min + 100。 ? IMPORTANT: The values of constants are substituted for the constant name during assembly time. They a NOT evaluated during execution time. Symbolic Constants ? Equalsign Directive ?Examples: Cost = 10 mov AX, Cost This is the same as mov AX, 10 ?Equalsign directives can be reassigned Cost = 10 ... Cost = 20 ... Cost = Cost + 10 Symbolic Constants ? EQU Directive: name EQU text ?Formats: name EQU expressions name EQU symbol ?Expression must be a valid integer expression ?Symbol must be a existing symbol name, already defined with = or EQU ?Cannot be redefined Symbolic Constants ? TEXTEQU Directive: ?Formats: name TEXTEQU %constExpr name TEXTEQU text name TEXTEQU textmacro ?Used to create a text macro ?Can be redefined Symbolic Constants ? TEXTEQU Directive: ?Example ContMsg TEXTEQU Press return CR = 0Dh LF = 0Ah Ending = 39。$39。 ?Then Msg db ContMsg, CR, LF, Ending assembles as Msg db Press return, 0Dh, 0Ah, 39。$39。 Symbolic Constants ? Comparison ?= and EQU value substitution TEXTEQU text substitution ?= and TEXTEQU allow redefinition EQU does not ?EQU allows floating point substitions = does not ?EQU and TEXTEQU allow = does not Symbolic Constants ? $ Operator ? The $ operator returns the current value of the location counter. We can use it to pute the string length at assembly time. .data LongString db “This is a piece of text that I“ db “want to type on 2 separate lines” LongString_length = ($ LongString) ? Note that we do not need to give a name to every line... Outline ? Basic Elements of Assembly ? Sample Program ? Assembling, Linking, and Running ? Defining Data ? Symbolic Constants
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