This means that the two's-complement value of AX will be the same, but the binary representation will be different.. Definitions and Theorems. e.g., ax - This means ax or eax. The state of flags after multiplication is undefined.Unsigned and signed division. In which case, CDQE copies the sign (bit 31) of the doubleword in the EAX register into the high 32 bits of RAX. For example, r8 means an 8-bit register.Memory and data transfer instructions do not affect flags.All arithmetic and bit manipulation instructions modify flags.Unsigned and signed multiplication. Thanks for contributing an answer to Stack Overflow!
Following is the list of instructions under this group −These instructions are used to call the interrupt during program execution.
operations like logical, shift, etc.
First of cltq is the name the gnu assembler uses for the x86-instruction called cdqe.
x86 instruction information compiled and authored by Rod Pemberton ---- NOTE: For brevity, most of this document will use 16-bit registers when there is a choice between either a 16-bit or 32-bit register. Signature (x86-cbw/cwd/cdqe proc-mode start-rip temp-rip prefixes rex-byte opcode modr/m sib x86) → x86 Returns x86 — Type (x86p x86), given (x86p x86). Instructions not so marked are not critical. The CWDE (convert word to double-word) instruction copies the sign (bit 15) of the word in the AX register into the high 16 bits of the EAX register.CBW and CWDE reference the same opcode. REPNE/REPNZ − Used to repeat the given instruction until CX = 0 or zero flag ZF = 1.
In the lists in this section, instructions marked with an asterisk (*) are particularly important.
This preserves the number 's sign: .DATA byte_val SBYTE -101 .CODE mov al, byte_val ; AL = 9Bh cbw ; AX = FF9Bh Note that both 9Bh and FF9Bh both equal decimal -101, the only difference is the storage size.. CBW − Used to fill the upper byte of the word with the copies of sign bit of the lower byte.
The value of AX after the cbw instruction will be FFF0h (a 16-bit -16 value, just like AL was originally an 8-bit -16)
The CWDE (convert word to double-word) instruction copies the sign (bit 15) of the word in the AX register into the high 16 bits of the EAX register.
Function: x86-cbw/cwd/cdqe
x86 integer instructions. On the x86 processor, instructions are variable-sized, so disassembling backward is an exercise in pattern matching. The x86 architecture is the most popular architecture for desktop and laptop computers. In the lists in this section, instructions marked with an asterisk (*) are particularly important. The CWD and CDQ mnemonics reference the same opcode. CBW and CWDE reference the same opcode.
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Following are the list of instructions under this group −These instructions are used to perform arithmetic operations like addition, subtraction, multiplication, division, etc.Following is the list of instructions under this group −These instructions are used to perform operations where data bits are involved, i.e.
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The first register in the pseudocode explanation receives the remainder and the second receives the quotient. This document contains very brief examples of assembly language programs for the x86.
Instructions not so marked are not critical. ... REPE/REPZ − Used to repeat the given instruction until CX = 0 or zero flag ZF = 1. The RCR instruction shifts the CF flag into the most-significant bit and shifts the least-significant bit into the CF flag (see Figure 7-11 in the IA-32 Intel Architecture Software Developer's Manual, Volume 1). The CWD instruction is intended for use when the operand-size attribute is 16 and the CDQ instruction … The result is stored into the destination.Some of the instructions have both 16-bit and 32-bit versions, but only the 32-bit versions are listed here.
In the lists in this section, instructions marked with an asterisk (On the x86 processor, instructions are variable-sized, so disassembling backward is an exercise in pattern matching. Most if not all of these instructions are available in 32-bit mode; they just operate on 32-bit registers (eax, ebx, etc.)
I understand your explanation of the sign bit of The last zero in 0FF0h was overlooked. Bit Manipulation Instructions . 05/23/2017; 9 minutes to read; In this article.
The CBW (convert byte to word) instruction extend s the sign bit of AL into the AH register. The CWD (convert word to doubleword) instruction extends the sign bit of AX into the DX register:
The first few instructions may not make any sense because you may have started disassembling in the middle of an instruction.
NOTE: this document assumes some familiarity with x86 instructions.
The C-language version of the rotation instructions incorporate the carry bit into the rotation.These instructions are remnants of the x86's CISC heritage and in recent processors are actually slower than the equivalent instructions written out the long way.After performing the operation, the source and destination register are incremented or decremented by sizeof(When debugging code, you may need to patch out some code. Let’s see how we can program in assembly language for processors in this family. ADD Eb Gb 00: ADD Ev Gv 01: ADD Gb Eb 02: ADD Gv Ev 03: ADD AL Ib 04: ADD eAX Iv 05: PUSH ES 06: POP ES 07: OR Eb Gb 08: OR Ev Gv 09: OR Gb Eb 0A: OR Gv Ev 0B: OR AL Ib 0C: OR eAX Iv 0D: PUSH CS 0E: TWOBYTE 0F: ADC Eb Gb 10: ADC Ev Gv 11: ADC Gb Eb 12: ADC Gv Ev 13: ADC AL Ib 14: ADC eAX Iv 15: PUSH SS 16: POP SS 17: SBB Eb Gb 18: SBB Ev Gv …
05/23/2017; 9 minutes to read; In this article. x86 Instruction Set Reference AND Logical AND.
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This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be (However, two memory operands cannot be used in one instruction.)
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