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I have searched on the net, but i couldn't find a clear example to understand what does this instruction do. So, if someone can give an example about this, it will be very helpful to me.
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Assuming you are talking about x86, the MOVSBL instruction extends a byte (8 bits) representing a signed number to 32-bit signed number. The remaining 24 bits are zeros or ones depending on the sign so that the two's complement value remains.
For MOVZBL, the low 8 bits of the destination are replaced by the source operand. the top 24 bits are set to 0. The source operand is unaffected. For MOVZBW, the low 16 bits of the destination are replaced by the source operand.
The CMP instruction compares two operands. It is generally used in conditional execution. This instruction basically subtracts one operand from the other for comparing whether the operands are equal or not. It does not disturb the destination or source operands.
The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH. These names refer to the same physical register. When a two-byte quantity is placed into DX, the update affects the value of DH, DL, and EDX.
The MOVS instruction is used to copy a data item (byte, word or doubleword) from the source string to the destination string.
The MOVSB (move string, byte) instruction fetches the byte at address SI, stores it at address DI and then increments or decrements the SI and DI registers by one. The MOVSW (move string, word) instruction fetches the word at address SI, stores it at address DI and then increments or decrements SI and DI by two.
Assuming you are talking about x86, the MOVSBL instruction extends a byte (8 bits) representing a signed number to 32-bit signed number. The remaining 24 bits are zeros or ones depending on the sign so that the two's complement value remains. Meaning, if you had a negative number, the upper 24 bits will be 1s, otherwise they will be zeroes.
Assembly - MOVS Instruction. The MOVS instruction is used to copy a data item (byte, word or doubleword) from the source string to the destination string.
Move with sign extend from byte to longword. In Intel syntax, the mnemonic of this instruction is MOVSX.
A C compiler may use this instruction when a variable of type int8_t needs to be converted to int, which happens automatically on arithmetic and a few other operations (integer promotion).
Because this instruction writes to all 32 (or 64) bits of the destination register, it avoids performance penalties that may result from writing to only the low 8 (or 16) bits of a register. A similar set of instructions allows extending with zero bits (MOVZX in Intel syntax, MOVZst in AT&T syntax (from size s to size t)).
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