Imul assembly. Section courante Gladir.

Imul assembly Covers fundamental concepts, instruction sets, & mem management. May 5, 2017 · You're using the three-operand variant of the imul instruction, which is defined in the instruction set reference as IMUL r64, r/m64, imm8 and means "Multiply the contents of r/m64 by imm8 and store the result in r64". movsx ecx, word [factor1] movsx eax, word [factor2] ; sign-extend inputs to 32-bit imul eax, ecx ; 32-bit multiply, result in EAX imul eax, eax ; and square the result This variant of imul was introduced with 386, and is available in 16 and 32-bit operand-size. Sau đây chúng ta sẽ lấy một số ví dụ minh họa việc sử dụng lệnh MUL và IMUL trong chương trình Ví dụ 1 : Chuyển đoạn chương trình sau trong ngôn ngữ cấp cao thành mã hợp ngữ : A = 5xA - 2xB Giả sử rằng A và B Jul 5, 2019 · I am a begginer with assembly i just started learning it and i don't get how the instruction IMUL really works For example i'm working on this piece of code on visual studio: Mat = 0A2A(hexadecimal) __asm { MOV AX, Mat AND AL,7Ch OR AL,83h XOR BL,BL SUB BL,2 IMUL BL MOV Ris5,AX } IMULInstruction • The IMULinstruction multiplies an 8-, 16, or 32-bit signed operand by either the AL, AX or EAX register (depending on the operand’s size). Phần thấp ở AX, phần cao ở DX. I thought that that the dividend was always placed in eax/ax and the one-operand instruction was just div/idiv ebx (or whatever register). g. The following instructions perform 8-bit signed multiplication of (-4 × 4) , producing -16 in AX : Apr 7, 2016 · Sorry - I always get mixed up with division in Assembly because I get confused with the registers. Game. Sep 18, 2008 · Since you're on x86 you need 4 mull instructions. However, the operands are x86 assembly tutorials, x86 opcode reference, programming, pastebin with syntax highlighting. Also see other links to docs and guides in the x86 tag wiki. Learn how to use the imul instruction to perform signed multiplication of bytes, words, or longs in IA-32 assembly language. In other words, since 0xB504F333 represents a negative value in 2's complement code (because its most significant bit is set), the instruction actually multiplies 0xB504F333-0x100000000=-1257966797 instead of 0xB504F333=3037000499 by itself. Since sub is usually unsigned sub how could I do something like in x86 MOV EAX,1 MOV EDX,3 SUB EAX,EDX,EAX ⭐ Kite is a free AI-powered coding assistant that will help you code faster and smarter. And also How many least-significant bits are the same for both an unsigned and a signed multiplication? – There's no immediate mul, but there is non-widening imul-immediate in 186 and newer, and imul reg, r/m in 386 and newer. IMUL with 2 operands works in a different way compared to MUL or IMUL with 1 operand. text global _start extern multiply _start: mov rcx, 5 ; a = 5 mov rdx, 10 ; b = 10 call multiply ; result is in rax call ExitProcess multiply: imul rax, rcx, rdx ret Learning Strategies. Opcode Mnemonic It guides readers through a vertical slice of a computer to develop an understanding of a variety of systems topics, including: how a computer runs a program, from a program expressed in a high-level language to low-level binary representation and circuits programming in C and Assembly (assuming a CS1 background) introduction to operating Oct 1, 2021 · 8086 Singed Multiplication Instruction (IMUL) IMUL (Integer Multiply) handles signed data operands. 而 IMUL 就是負責處理 signed 的部分，IMUL 的用法有以下幾種： imul source1 imul dest, source1 imul dest, source1, source2 這樣一來使用組合就有很多種了，以下用一張圖來說明： 除法(devide) Jan 8, 2012 · MOV EAX,0xB504F333 MOV ECX,0xB504F333 IMUL ECX Must indeed produce 0x15F61998 in EDX and 0x9EA1DC29 in EAX. Now a uint64_t needs 2 registers, so how do I specify the output and the constraints of the asm block? Oct 18, 2010 · In these cases, the low 16 or low 32 bits of the result is the same for imul as they would be for an equivalent mul, only the flags (CF and OF) may differ. If only 1 register provided, multiplies it by eax. Without MUL the normal approach is "SHIFT LEFT and TEST and ADD" in a loop, like this: Data sizes in assembly have slightly different terminology to get used to: •A byteis 1 byte. second) operand must be a register. Performs a signed multiplication of two or three operands. imul arg . Jan 2, 2019 · idiv divides edx:eax by the explicit source operand. Under what circumstances does imul write to edx? I checked multiple x86 documentation sites, and they all seem to have conflicting information. この命令は、レジスターの内容を「arg」で除算する。 下表 imul — Integer multiplication The imul instruction has two basic formats: two-operand (first two syntax listings above) and three-operand (last two syntax listings above). com - Langage de programmation - Assembleur 80x86 - Lexique et dictionnaire d'instruction assembleur 80x86 - Instruction IMUL Apr 15, 2018 · Is it possible to calculate result of multiplication without using instructions MUL, IMUL, SHL, SHR, LOOP, JMP in x86 assembly language? Yes. mul. Aug 5, 2015 · Bài giảng môn Assembly 49 MUL BX 4294836225 FFFE0001 FFFE 0001 1 IMUL BX 1 00000001 00000 0001 0 Ví dụ 3 : Giả sử rằng AX=0FFFh INSTRUCTION Dec product Hex Product DX AX CF/OF MUL BX 16769025 00FFE001 00FF E001 1 IMUL BX 16769025 00FFE001 00FF E001 1 Ví dụ 4 : Giả sử rằng AX=0100h và CX=FFFFh INSTRUCTION Dec product Hex It was my understanding that the output of imul is edx:eax, meaning imul should overwrite edx. IMUL r64, r/m64, imm8* r64 = r/m64 * sign-extended imm8 * If the first two operands are the same, the second one can be left out when using nasm or . The operands can be positive or negative. Syntax IMUL r/m32 EDX:EAX = EAX * r/m doubleword IMUL r32,r/m32 Nov 30, 2020 · Related: problem in understanding mul & imul instructions of Assembly language / MUL instruction doesn't support an immediate value re: multiply by a constant (as an immediate) with imul bx, bx, 10 – IMUL BX -256 FFFFFF00 FFFF FF00 0 Ví dụ 5 : Giả sử rằng AL=80h và BL=FFh INSTRUCTION Dec product Hex Product DX AX CF/OF . Which would perform effectively eax / ebx with the quotient in eax and the remainder in edx. What you're saying is valid for IMUL with 1 operand, quote from the same page in the manual: IMUL r/m32: EDX:EAX ← EAX ∗ r/m32. Syntax to read IA32 register with offset in GDB? 1. ELSE IF (NumberOfOperands = 2) THEN temp ← DEST ∗ SRC (* Signed multiplication; temp is double DEST size ) DEST ← DEST ∗ SRC (Signed multiplication *) Students will know that MUL and IMUL instructions are very helpful in performing multiplication for unsigned and signed integers. imul clears the overflow and carry flags under the following conditions: Table 2-5 Clearing OR and CF Flags -- imul May 27, 2022 · x86 Assembly quick links: registers • move • jump • calculate • logic • rearrange • misc. to optimize uint64_t = u32 * (uint64_t)u32. Aug 5, 2017 · mul and imul also set FLAGS differently: CF=OF= whether or not the full result fits in the low half. Split the 64bit quantities into two 32bit words and multiply the low words to the lowest and 2nd lowest word of the result, then both pairs of low and high word from different numbers (they go to the 2nd and 3rd lowest word of the result) and finally both high words into the 2 highest words of the result. The destination register is on the right. That's because IMUL treats its operands as signed. For imul reg,r/m or imul reg, r/m, imm, the "low half" is the destination reg; the high half isn't written anywhere. Performs a signed multiplication of two operands. MUL BL 128 7F80 7F 80 1 IMUL BL 128 00080 00 80 1 Một phần của tài liệu Bài giảng hợp ngữ (assembly) (Trang 52 - 53) Dec 27, 2017 · IMul [Toán hạng nguồn] Div [Toán hạng nguồn] IDiv [Toán hạng nguồn] Tác dụng: Lệnh Mul (Multiply): Thực hiện phép nhân trên số không dấu. imul eax, 10 is not clearing edx. IMUL r32,imm32: doubleword register = r/m32 * immediate doubleword. You can still explain how it works, of course :) Probably the usual case of disabled optimization, otherwise the compiler is clever enough to use a single imul. •A double wordis 4 bytes. The three-operand form of imul executes a signed multiply of a 16- or 32-bit immediate by a register or memory word or long and stores the product in a specified register word or long. I don't know which assembler you're using imul vs. Sep 3, 2017 · (Although doing two extended-precision shifts is not wonderful either. And here is registers after imul registers after imul Jun 1, 2023 · The low n bits of an n x n => 2n product don't depend on signed vs. The two-operand form of IMUL is easier to use. The result is equivalent to sign-extending (imul) or zero-extending (mul) both inputs to the destination width and then doing a non-widening multiply, although of course the actual implementation would do something more efficient. Learn how to use imul, mul, div, and idiv instructions to perform signed and unsigned multiplication and division in IA-32 assembly language. Для умножения чисел со знаком предназначена команда IMUL. IA32 Assembly: lea instruction. The first operand (second source) can be a register or memory. There is also another variant of this instruction, which takes a 32-bit immediate, but it is impossible to tell which variant Nov 23, 2015 · AT&T assembly syntax just happens to be "backwards" from the way everyone else does it. It multiplies the second operand by the third and places the result in the first, truncating in case of overflow. Feb 15, 2019 · sourceの値をdestinationに掛けて、destinationに入れる操作。例えば、eax=3, ebx=2で imul eax, ebx なら、eaxにebxを掛けてeaxに入れるのでeax=6, ebx=2となる。 idiv idivはInteger DIVide (signed)を表します。 Dec 25, 2013 · I assumed I could cascade multiplies with the 64-bit imul rcx instruction (that produces a 128-bit result in rdx:rax) in the same way I could do the same with unsigned operands with the mul rcx instruction but the answers with imul are wrong. It has no effect on the imul instruction, though. The form that takes a single 32bit argument (memory or register) always returns the result in the EDX:EAX pair. Apr 21, 2019 · About IMUL. However, I just ran into an issue where. The Carry flag indicates whether or not the upper So I continued with imul mov bx 0x2 imul bx Result of eax : 0xfffffffe and eflags : sf set, but cf is not set Then I imul again, this time with a negative number. • The instruction formats are: IMUL r/m8 IMUL r/m16 IMUL r/m32 EAX x r/m32 EDX EAX According to Agner Fog's testing (and other stuff like AIDA64) Intel CPUs since Core2 have had imul r32,r32, imm latency of 3c, throughput one per 1c. 6B /r ib IMUL r16, r/m16, imm8 word register ← r/m16 ∗ sign-extended immediate byte. It is intended to be accessible by people who know a little bit of C and a little bit of assembly. x86-assembly-cheat-sheet: A must-have for quick reference in x86 Assembly. (This is true across all mainstream and low-power Intel/AMD that are still rele Nov 22, 2024 · Hence, the C compiler only needs what imul provides, and since imul is easier to use than mul, the C compiler uses imul to avoid needing mov instructions to get data into / out of eax. See the insn ref manual entry for IMUL. When the operand is a byte, it is multiplied with AL register and when it is a word, it is multiplied with AX register. Oct 16, 2020 · The immediate form of the IMUL instruction, opcodes 6B and 69, actually takes three operands, all of the same size (here 16 bits): IMUL r, r/m, imm. Source1 and Source2 get multiplied with each other and result is stored in destination operand. I also know that the quotient is stored in eax and the remainder in edx. I suspect there is some trick to make this work, maybe mix imul and mul instructions - or something Apr 24, 2016 · Yes you can. cast the operand(s) to a signed type twice the register length. x86 Assembly Guide. It just saves you from having to repeat the same register twice as both the destination and first source when you don't want to take advantage of the non-destructive separate destination. exe+C00193 The instruction itself is not the problem, its signed mulitply with three operands: destination, source1 and source2. imul trivia: Only the upper half of the full-multiply (N x N => 2N) result differs between imul and mul. This instruction has three forms, depending on the number of operands Mar 6, 2017 · imul ax, ax ;16x16->16, Lower WORD of the result is ax imul rax, rax ;64x64->64, Lower QWORD of the result is rax Only the single-operand version is of the first form. MUL と同じであるが、符号付き数値のみを扱う。 div arg . - 7etsuo/x86 Aug 27, 2022 · Footnote 1: Including the 2 and 3 operand forms like imul cx, dx, 123 that don't write the high half anywhere. //Multiply by 7 mov ecx,eax shl eax,3 //*8 sub eax,ecx Jun 16, 2021 · mul vs. It also knows if overflow happened for the same reason. Apr 3, 2016 · If you want to write C code so that the compiler emits imul with one operand then the only way is to use widening signed multiplication, i. Computer Science 217: Introduction to Programming Systems The imul instruction knows the sign of its operands and therefore if it needs to sign extend or not. 1. Your code is multiplying EAX by 22 (0x16) and putting the result into EAX. May 24, 2014 · The MUL and IMUL (Integer MULtiplication) instructions are used to multiply two signed (with IMUL) or unsigned (with MUL) numbers. exe+1F745D - 69 C0 93 01 00 01 - imul eax,eax,Game. Once you have the result of the IMUL, you need to store the result in mat3[0]. Since you cannot move DX:AX with one instruction, you need two. The result (i. When multiplying N-bit number by other N-bit one, the low N bits of the result are the same no matter whether you do the signed or unsigned multiplication - you can read first chapter of my tutorial, which I have written to explain such things (though I'm not sure whether I wrote it clearly enough there, if you have any suggestions or questions, please let me know). The only question is how much better it is than the alternatives. Lệnh này thực hiện như sau: lấy nội dung/giá trị hai [Toán hạng Jan 16, 2016 · when I have the the operation . In-order Atom (pre-Silvermont) has 13c latency (and not pipelined) for imul r64, r64, but 1c latency for shl r64, cl, so this could win there. Registers for IMUL instruction. See full list on tutorialspoint. x86-64 has hundreds of instructions, and compiling programs to the most efficient machine code requires a good understanding of all of them–indeed, the fastest C compiler May 18, 2019 · When using IMUL instruction with a single 8-bit operand, the result is stored in AX register. definition of negative is that their highest ranked bit equals 1, so FFCE is negative, because 1111 1111 1100 1110 and processor cannot work with negatives, we need to have positive, that means we negate this number (or processor does this based on highest ranked bit automaticallly) Oct 18, 2015 · Unfamiliar syntax for the "imul" instruction in x86 assembly. Performs a signed multiplication of two operands. imul clears the overflow and carry flags under the following conditions: Table 2-5 Clearing OR and CF Flags -- imul However turn over to IMUL and you'll see there are many forms of it that accept an immediate. As a second step, since C compilers use the multiple-operand form of imul a lot, Intel and AMD invest effort into making it as fast as possible. – 3/4/16 1 x86 Assembly Crash Course Don Porter Registers ò Only variables available in assembly ò General Purpose Registers: ò EAX, EBX, ECX, EDX (32 bit) May 30, 2020 · What is Imul Assembly? Description. Presumably the designers went with the mnemonic imul because the forms with an 8 bit immediate do sign-extend that immediate. Jun 27, 2023 · In this video, you will learn how to apply signed and unsigned multiplication instructions through MUL and IMUL in x86. imul — Integer multiplication The imul instruction has two basic formats: two-operand (first two syntax listings above) and three-operand (last two syntax listings above). Assembly instructions can have suffixes to refer to these sizes: •bmeans byte •wmeans word •lmeans double word •qmeans quad word mov al, 48 mov bl, 4 imul bl ; AX = 00C0h (decimal +192), OF = 1 Because AH is not a sign extension of AL , the Overflow flag is set to 1 . Same for AVX instructions like vpand xmm0, xmm0, xmm1 . Jul 14, 2016 · Description. You are dividing 4294901760 by -61184, giving -70196 with a remainder of 29696. 6B /r ib IMUL r32, r/m32, imm8 doubleword register ← r/m32 ∗ sign-extended immediate byte. x86-64 assembly language is a human-readable version of this machine code. What sorcery is this? This mysterious transformation is effectively multiplying by 1/10 as a substitute for divide by 10. thx for help my question is about ax value received from code below? mov al,22h mov cl,0fdh imul cl Actual machine result: ff9a What I expected: 00:9a (by multiplying in binary) The first numb Jul 31, 2021 · imul <source> imul <dest>, <src/imm> imul <dest>, <src>, <imm> In all cases, the destination operand must be a register. This instruction has three forms, depending on the number of operands. For the multiple operand multiply instruction, byte operands are not supported. Assembly Language: Part 2. This video is part of my free Foundati Nov 27, 2009 · C:\Windows\system32>debug -a 17CC:0100 imul ax 17CC:0102 -u 17CC:0100 F7E8 IMUL AX 17CC:0102 0000 ADD [BX+SI],AL -q Using the debug command it can be verified that "imul ax" will assemble (and is therefore a valid command in 80x86 assembler). The single-operand form of imul executes a signed multiply of a byte, word, or long by the contents of the AL, AX, or EAX register and stores the product in the AX, DX:AX or EDX:EAX register respectively. •A quad wordis 8 bytes. A shift left is a multiply by two shl - (Larger). 65 mov eax, ebx mov ecx, 0x0. the full result is the zero-extension or sign-extension of the low half). Эта команда имеет три формы, различающиеся Jun 10, 2016 · IMUL comes in the same two versions, but treats the values as signed. Section courante Gladir. . Signed multiplication of 2 operands. I have the following code. Princeton University. See Intel's instruction manual entry. AH=FF. – Oct 2, 2021 · NASM (and most other assemblers including GAS) accept imul x, imm as short-hand for imul x, x, imm. unsigned. The sequence basically looks like a(n)=a(n-1)*a(n-2) with first two elements being -1 and -3. Arithmetic & Logic Operations . Sep 29, 2012 · @coolbartek Look up the CPU manual. I want to use the UMULL instruction from the ARM CPU to multiply 2 uint32_t and get the result immediately into a uint64_t. 65 ;; how do this? mul ecx mov ebx, eax Oct 29, 2012 · Something I do not get though is how most instruction sets have a IMUL and IDIV but not a ISUB and an IADD. GCC's assembler syntax. ) Intel's original Pentium (P5) had imul that takes 9c. mov bx -1 imul bx Result eax:ffff0002 eflags sf set, no cf. You can add and substract to correct for non-powers of two along the way. One-operand form — This form is identical to that used by the MUL instruction. e. imul ax,ax is a perfectly good instruction. Look at the C source and generated assembly for this function. Quote: IMUL r32, r/m32: doubleword register ← doubleword register ∗ r/m32. This page is meant to consolidate GCC's official extended asm syntax into a form that is consumable by mere mortals. ADC - add a value, plus ADD - add two registers together DEC - decrement by 1 DIV - unsigned divide IDIV - signed divide IMUL - signed multiply INC - increment by 1 MUL - unsigned multiply NEG - two's complement (multiply by -1) SBB - subtract with borrow (carry flag) SUB - subtract LEA - load effective address (formed by some expression Documentation Home > IA-32 Assembly Language Reference Manual > Chapter 2 Instruction-Set Mapping (imul) Next: Unsigned Divide (div) Unsigned Multiplication of AL Dec 30, 2023 · So I have some assembly code: MOV AL, 48 MOV BL, 4 IMUL BL ; AX = 00C0h, AH = 00 is positive and AL = C0 is negative so CF = OF = 1 MOV AX, 0x8760 MOV BX, 0x100 IMUL BX ; DX:AX = FF87:6000, DX is negative and AX is positive so CF = OF = 1 but in this one: Jul 13, 2024 · I want to use a imul instruction with 3 operands. I. if they match it's positive output, don't match it's negative, and if that isn't the case overflow happened. Jan 21, 2025 · Welcome to Lec#11 of our Computer Organization and Assembly Language (COAL) series! In this lecture, we delve into the MUL and IMUL instructions, two fundame Oct 22, 2016 · How can I multiply float in Assembly? I have a value in ebx and want mutiply this for 0. Can you use imul to multiply a register by itself? 1. They will also learn the way these two differs from each other and the way we can use the suitable ; IMUL comes with multiple operands so the students will be able to distinguish the flexibility provide by IMUL over MUL Feb 9, 2014 · See also problem in understanding mul & imul instructions of Assembly language re: different forms of multiply, including imul reg, r/m instead of the one-operand widening form. Carnegie Mellon Arithmetic Expression Example long arith (long x, long y, long z) { Sep 1, 2014 · IMUL : Cette instruction permet d'effectuer une multiplication signée (nombre entier). mov eax, 0 mov ebx, 0 mov al, 48 mov bl, 4 call dumpregs imul bl call dumpregs 48 * 8 is 192(C0 in hex), which is correctly stored in AX register as 00C0(see the output below). See the syntax, operation, description, and examples of each instruction. To multiply AH * AL and get the result in AX, you should have used imul ah. AX=AL*nguồn 8bit. I can understand why eax is ffff0002. (And 64-bit operand-size in 64-bit mode). There are many forms of the imul instruction. May 30, 2020 · In this video, you will learn:-What is MUL instruction?-How to use MUL instruction?-How to calculate flag bits in-case of MUL instruction?-Working of MUL ins Jan 23, 2020 · What is Imul Assembly? Description. See the operation, description, flags, and examples of imul with different operand forms. The MUL (unsigned multiply) instruction multiplies an 8-, 16-, or 32-bit operand by either AL, AX, or EAX. Aug 27, 2016 · The other ways to nest the loops might be better or worse for performance with large matrices, but the only really good ways to do this (for large matrices) involve transposing one of the input matrices so you can loop over contiguous memory elements in both matrices at once (since transposing costs O(n^2) time, but speeds up the O(n^3) step which traverses the transposed array repeatedly Nov 19, 2015 · Since imul already provides a 64x64->128 bit multiply, I don't see the point of this. Feb 18, 2015 · idiv part of answer mov AX, FFCE idiv AH AX=FFCE. Since Nehalem, 64-bit multiplies are also that fast. •A wordis 2 bytes. . mov eax, 0 mov ebx, 0 mov ecx, 0 mov al, [sbAval+esi] mov bl, [sbAval+esi] power: imul ebx cmp ecx, 2 je powerDone inc ecx jmp power sbAval is SBYTE data type. com The IMUL instruction allows the multiplication of two signed operands. IA32 Assembly Move Instruction. destLO [in] The address of the low 32 bits of the result. Jul 14, 2016 · Signed multiplication of 2 operands. IDIV ecx in assembly, then i have read that the that the value in edx:eax is divided by the operand ecx. Visual Studio extension for assembly syntax highlighting and code completion in assembly files and the disassembly window - IMUL · HJLebbink/asm-dude Wiki Jan 29, 2022 · Only imul exists in a form that doesn't waste time writing a high-half result, so compilers (and humans) use imul regardless of signedness, except when they specifically want a high-half result, e. When using a single operand multiply instruction, the imul is the same layout as the mul (as previously presented). Normally you'd use that form for non-widening signed or unsigned math, but if you want to detect when an unsigned multiply wrapped, your best bet is to just use mul even though that forces you to use EAX and have the output in EDX:EAX. 0. Since edx is 0, edx:eax is a positive number. Nov 19, 2019 · Item Description; destHI [in] The address of the high 32 bits of the result. Could You please advise what procedure should be followed to solve below: mov ax, 0835 h mov cv, 005d h idiv cl ax = ? Correct answer: 3716 My answer: 0016 (I get it by converting 0835h to 2101 Dec 17, 2016 · @RossRidge: IMUL sets CF and OF if the upper-half is not the sign-extension of the low half (even the multi-operand versions work that way, so detecting unsigned wraparound when using 2 or 3 operand imul can't be done from just the flags) – Jan 13, 2015 · You can find really cool assembly code demonstrating the concept in Agner Fog's assembly library. x86 Instruction Set Reference FMUL/FMULP/FIMUL Multiply. Unfortunately shl r32, cl takes 4c, so this idea is a non-starter on P5. Contents: Registers | Memory and Addressing | Instructions | Calling Convention. Oct 16, 2015 · - IMul Ax, Bx, 20 ; lệnh này có ba toán hạng, [Toán hạng đích] là thanh ; ghi 16 bit (Ax), [Toán hạng nguồn] là thanh ghi 16 bít ; (Bx) và một hằng số (20) Lệnh Imul ở trên là một lệnh nhân mới của vi xử lý Intel 80286. Machine Level – Assembly (x86-64) basics . So a separate multi-operand mul isn't needed. The syntaxes are the following. See @phuclv's answer on problem in understanding mul & imul instructions of Assembly language for more details, and of course Intel's instruction set reference manuals for mul and imul: Aug 22, 2020 · Unlike with mul/imul (where you should normally use faster 2-operand imul r32, r/m32 or 3-operand imul r32, r/m32, imm8/32 instead that don't waste time writing a high-half result), there is no newer opcode for division by an immediate, or 32-bit/32-bit => 32-bit division or remainder without the high-half dividend input. Nếu nguồn là 16bit thì kết quả lưu vào DX AX =AX*nguồn 16bit. Sep 21, 2016 · For your code, instead of moving mat2[0] into BX, you could simply IMUL it directly from memory - and yes, you should use IMUL since you want an signed multiply. The two-operand form multiplies its two operands together and stores the result in the second operand. (There's also a 3-operand form, imul r64, r/m64, imm8/32, which allows you to copy-and-multiply x86 assembly tutorials, x86 opcode reference, programming, pastebin with syntax highlighting. The only difference will be in the flags being set, which are rarely looked at, especially by compiler x86-64 machine code is the native language of the processors in most desktop and laptop computers. I think Intel picked imul as the one that would have multiple explicit operands so that imul r32, r32, sign-extended-imm8 would make more sense, because sign-extension is probably more useful than zero-extension. intel_syntax Jan 8, 2020 · (The imul doesn't destroy RBX, so the upper 32 bits of the value you put into RBX is still there if you want to read it later. MUL/IMUL [r/m32] IMUL [reg], [r/m32] IMUL [reg], [r/m32], [immediate] So, IMUL can have different forms, but the type of operands to be used are strictly fixed, while MUL has only one imul instructions for both 8-bit and 16-bit Jul 19, 2019 · On all modern x86 CPUs, LEA is a single uop. Here I have 9C stored in eax and ebx registers before imul. Is the destination operand the first or last? I searched the web and got contradictory informations. Regarding your workaround/emulation of movzx , it would be better to use: xor bx, bx ; clear BX (upper and lower bits) mov bl, centerBot ; copy centerBot to the lower bits of BX Dec 22, 2019 · IMUL:(signed multiply) 有號數的乘法 ＊這邊要注意carry flag跟overflow flag的使用，如果上半部的bit不為其下半部的延伸，則CF = 1, OF = 1 ＊還有一點，當我們用有號數的乘法，去操作無號數的乘法時，CF, OF不代表bit的上半部是否為全零的狀態。 Apr 26, 2015 · For IMUL: The CF and OF flags are set when the signed integer value of the intermediate product differs from the sign extended operand-size-truncated product, otherwise the CF and OF flags are cleared. 4. (i. • FPU All arithmetic instructions are executed in (one of) the ALU s. The Kite plugin integrates with all the top editors and IDEs to give Assembly Code: section . Feb 28, 2010 · I would like to introduce some assembly code into a c99 codebase. Hence in 32-bit mode the following code will produce the expected output Jul 25, 2013 · Unfamiliar syntax for the "imul" instruction in x86 assembly. ) Even better, imul eax, ebx, 0xfbc7a1ce could have avoided a mov . The assembly still doesn't use a div instruction, by there is a multiply by a bizarre number: -858993459 (in hex 0xcccccccd). There are several different assembly languages for generating x86 machine code. I use imul for Oct 29, 2017 · As said by Fifoernik, if you want to multiply a 16 bit register for a constant, you may need up to 32 bit result (furthermore you can have negative input-number); all the routines I've written are successfully tested and they are about three time more fast than IMUL (8086 assembly guides of Peter Norton): Sep 20, 2016 · You're also using imul incorrectly: imul ax sets DX:AX = AX * AX (producing a 32-bit result in a pair of registers). Sep 22, 2019 · There is no imul instruction where the destination is memory -- so the last operand (the destination and first source) must be a register. Shifts and adds/subs A shift right is a divide by two shr - (Reduce). This guide describes the basics of 32-bit x86 assembly language programming, covering a small but useful subset of the available instructions and assembler directives. The operation of MUL and IMUL instructions are same. I was writing this simple programm to calculate a ith element of a recursive sequence. src0 [in] The value to multiply with src1. Start Small: Begin with simple programs and gradually increase complexity. imul is also 1 uop, but mov+shl+add is 3 for the front-end. But the high half does. Mar 18, 2019 · command imul destination, source1, source2. aqhbel txco whtijik exnwqd pjzxccxk myjmhqo omjf rdy bjkdnc yfdqwv hsdg oua lyus yxjm mjkh