NASM 2.05 based x86 Instruction Reference[ch204]
A.5.181 MOVSX, MOVZX: Move Data with Sign or Zero Extend MOVSX reg16,r/m8 ; o16 0F BE /r [386] MOVSX reg32,r/m8 ; o32 0F BE /r [386] MOVSX reg32,r/m16 ; o32 0F BF /r [386] MOVZX reg16,r/m8 ; o16 0F B6 /r [386] MOVZX reg32,r/m8 ; o32 0F B6 /r [386] MOVZX reg32,r/m16 ; o32 0F B7 /r [386] MOVSX sign-extends its source (second) operand to the length of its destination (first) operand, and copies the result into the destination operand. MOVZX does the same, but zero-extends rather than sign- extending.