Slide 6.3: Zero/sign extension of integers
Slide 6.5: MOVSX instruction
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MOVZX Instruction

The MOVZX instruction (move with zero-extend) copies the contents of a source operand into a destination operand and zero-extends the value to either 16 or 32 bits.
Zero Extension of an Integer
Source (8 bits) Destination (16 bits)
1 0 1 0 1 0 1 0  0 0 0 0 0 0 0 0 1 0 1 0 1 0 1 0

MOVZX — Move with Zero-Extend (386+)

Usage: MOVZX 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 zero-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

†This instruction is used to copy an 8-bit or 16-bit operand into a larger destination, which must be a register.

 AX = SWORD  EAX = SWORD  EAX = BYTE 
 .data
 var    SWORD  0F1F0h
 .code
 mov    eax, 0
 movzx  ax, var
 call   WriteHex
 
 .data
 var    SWORD  0F1F0h
 .code
 mov    eax, 0
 movzx  eax, var
 call   WriteHex
 
 .data
 var    BYTE  0F0h   
 .code
 mov    eax, 0
 movzx  eax, var
 call   WriteHex
 Output  Output  Output