STRINGS

• String


  A series of ASCII characters, typically terminated with a NULL
• The NULL is a non-printable ASCII control character that can be used to mark the end of a string
• String instructions


  Ease string manipulation, can operate on 8-,16-,32- or 64-bit operands
• Reading and Writing String instructions

  1. LODS (Load string)

  2. STOS (Store string)

  3. MOVS (Copy string to desired destination)
• Direction flag (DF)


  Determines whether the index registers are incremented or decremented
• CLD


  Clears the direction flag, index registers are incremented
• STD


  Sets the direction flag, index registers are decremented
• REP


  Unconditional repeat prefix which causes the instruction to repeat according to the value of rcx
• REPE/REPZ


  Similar to REP but immediately terminates when ZF = 0
• REPNE/REPNZ


  Similar to REP but immediately terminates when ZF = 1
• LEA (Load Effective Address)


  Loads the effective address of the memory operand into the specified register, without loading the value
• Comparison String instructions


  1. CMPS (Compares two strings per element)

  2. SCAS (Scans a character in a string)