MOVSX Instruction

The MOVSX instruction (move with sign-extend) copies the contents of a source operand into a destination operand and sign-extends the value to either 16 or 32 bits.

Sign Extension of an Integer
Source (8 bits) Destination (16 bits)
0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 1
1 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 0

MOVSX — Move with Sign-Extend (386+)
Usage: MOVSX dest, src

Flag O D I S Z A P C
Result                

Copies a byte or word from a source operand to a destination operand and sign-extends into the upper half of the destination.
Clocks
Operands 286 386 486 Size Bytes
reg, reg   3 3 3
reg, mem   6 3 3-7

 AX = BYTE   SDWORD = SWORD   SWORD = SDWORD  


 .data


 var    BYTE  0F0h


 .code


 mov    eax, 0


 movsx  ax, var


 call   WriteHex
 



 .data


 var1   SWORD   -3600


 var2   SDWORD  ?


 .code


 


 


 mov    eax, var2


 call   WriteInt
  




 .data


 var1   SWORD   ?


 var2   SDWORD  0FFFFF123h


 .code


 


 


 


 movsx  eax, var1


 call   WriteHex
 

 Output  Output  Output
   



  -3600     0FFFFF123h  


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