remainder in assembly language remainder in assembly language

x86 Assembly Language - Integer Multiplication, Division, and Modulus Operations Bradley Sward 2.5K subscribers Subscribe 93 Share 11K views 2 years ago A look at signed and unsigned integer. The product is in AX. Parity Flag (PF) It indicates the total number of 1-bits in the result obtained from an arithmetic operation. when operand is a word: AX = (AX) / operand, DX = remainder (modulus). The three main regional variants spoken by Saudis are Najdi Arabic (about 14.6 million speakers[483]), Hejazi Arabic (about 10.3 million speakers[484]), and Gulf Arabic (about 0.96 million speakers[485]). Each open file is associated with a file pointer that specifies an offset in bytes, relative to the beginning of the file. If you compute modulo a power of two, using bitwise AND is simpler and generally faster than performing division. These 32-bit registers can be used in three ways . I heading) ARTICLE I (720 ILCS 570/100) (from Ch. The following program adds up two 5-digit decimal numbers and displays the sum. Which machine are you programming for? In the above example of displaying a character string, the registers EAX, EBX, ECX and EDX have been used by the INT 80H function call. You can make use of Linux system calls in your assembly programs. Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2. Follow Up: struct sockaddr storage initialization by network format-string, Is there a solution to add special characters from software and how to do it. Assembly language is dependent upon the instruction set and the architecture of the processor. He has earned a Masters degree in Software Engineering from DePaul University, a Masters degree in Computer Science from the University of Illinois at Springfield, and two Bachelors degrees in Computer Science and Molecular Biology from Benedictine University. For closing a file, perform the following tasks . The high-order 32 bits are in EDX and the low-order 32 bits are in EAX. A 16-bit Data Segment register or DS register stores the starting address of the data segment. Ex: MOV AX,9031h Ax = 9031h. My code is GPL licensed, can I issue a license to have my code be distributed in a specific MIT licensed project? Is there something like a modulo operator or instruction in x86 assembly? If speed isn't important, there are several options, all of them easy to look up. be register or memory location only. This browser is no longer supported. When you need to use some sequence of instructions many times in a program, you can put those instructions in a macro and use it instead of writing the instructions all the time. In direct memory addressing, one of the operands refers to a memory location and the other operand references a register. How to use the div instruction to find remainder in x86 assembly? Conditional execution in assembly language is accomplished by several looping and branching instructions. Check The netwide assembler (NASM) website for the latest version. You can declare various constant values, file names, or buffer size, etc., in this section. Assembly Language The remainder of this course will involve software as well as hardware structures, both in examples and exercises. The OR instruction is used for supporting logical expression by performing bitwise OR operation. DIV BL ; Al (quotient)= 08h, Ah(remainder)= 01h. x86 assembly (on Win32) "SPEED!" seems to be hugely important here, and we all know nothing beats assembly language in that regard. The DEC instruction has the following syntax . Not the answer you're looking for? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Let us take up another example. The top of the stack, which points to the last data item inserted into the stack is pointed to by the SS:ESP register, where the SS register points to the beginning of the stack segment and the SP (or ESP) gives the offset into the stack segment. For writing to a file, perform the following tasks . Fixed point is easy : if you decide you want 8 fractional bits, just divide 2^8 * remainder / denominator, and use the size of that operation's remainder to determine rounding. Following are some examples of typical assembly language statements , The following assembly language code displays the string 'Hello World' on the screen , When the above code is compiled and executed, it produces the following result , Make sure you have set the path of nasm and ld binaries in your PATH environment variable. The following table shows the positional values for an 8-bit binary number, where all bits are set ON. The x86 exception is #DE - divide exception. The following code shows this , Such conversions, however, have an overhead, and assembly language programming allows processing numbers in a more efficient way, in the binary form. If this is 1, the number is odd, else the number is even. Put the file access mode in the ECX register. So, the parity bit is used to make the number of bits in a byte odd. Code: [Select] SYS_EXIT equ 1 SYS_READ equ 3 SYS_WRITE equ 4 System calls are APIs for the interface between the user space and the kernel space. For other operand-sizes, use cbw (AL->AX), cwd (AX->DX:AX), cdq (EAX->EDX:EAX), or cqo (RAX->RDX:RAX) to set the top half to 0 or -1 according to the sign bit of the low half. Connect and share knowledge within a single location that is structured and easy to search. AL stores the answer and the remainder is in AH. The first operand defines the length of the data. As mentioned earlier, this is performed by the JMP instruction. We have already used the system calls. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, @bluebk where do you get integer overflow? Syntax The INC instruction has the following syntax INC destination The operand destination could be an 8-bit, 16-bit or 32-bit operand. Destination Index (DI) It is used as destination index for string operations. The first operand in all the cases could be either in register or in memory. The dividend is assumed to be 32 bits long and in the DX:AX registers. - the incident has nothing to do with me; can I use this this way? for an example of x86 vs. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? The following table shows some of the system calls used in this tutorial , The following example reads a number from the keyboard and displays it on the screen . The operand destination could be an 8-bit, 16-bit or 32-bit operand. The MUL (Multiply) instruction handles unsigned data and the IMUL (Integer Multiply) handles signed data. On Unix/Linux systems, the kernel delivers a SIGFPE arithmetic exception signal to processes that cause a #DE exception. If you have done everything correctly, it will display 'Hello, world!' RISC-V pronounced as "RISC-ve", is an open-source standard Instruction Set Architecture (ISA), designed based on Reduced Instruction Set Computer (RISC) principles. The ADD and SUB instructions are used for performing simple addition/subtraction of binary data in byte, word and doubleword size, i.e., for adding or subtracting 8-bit, 16-bit or 32-bit operands, respectively. Example Binary number 1000 1100 1101 0001 is equivalent to hexadecimal - 8CD1. Each statement follows the following format . For example: factorial of 5 is 1 x 2 x 3 x 4 x 5 = 5 x factorial of 4 and this can be a good example of showing a recursive procedure. contains random data) - BlackBear Oct 5, 2013 at 21:08 I've tried using mov A, edx as well and it didn't work also - rullzing Oct 5, 2013 at 21:14 What assembler are you using? Following are the conditional jump instructions used on signed data used for arithmetic operations , Following are the conditional jump instructions used on unsigned data used for logical operations , The following conditional jump instructions have special uses and check the value of flags , The syntax for the J set of instructions , The following program displays the largest of three variables. When two one-word values are multiplied . All the syscalls are listed in /usr/include/asm/unistd.h, together with their numbers (the value to put in EAX before you call int 80h). The macro begins with the %macro directive and ends with the %endmacro directive. The remainder has the same sign as the dividend; the absolute value of the remainder is always less than the absolute value of the divisor. 1 and 6 should be displayed together (16). A nonzero result clears the zero flag to 0, and a zero result sets it to 1. Affordable solution to train a team and make them project ready. However, memory-to-memory operations are not possible. The sys_brk() system call is provided by the kernel, to allocate memory without the need of moving it later. Direction Flag (DF) It determines left or right direction for moving or comparing string data. How can this new ban on drag possibly be considered constitutional? Data segment It is represented by .data section and the .bss. The high-order (leftmost) portion gets stored in DX and the lower-order (rightmost) portion gets stored in AX. Code Segment It contains all the instructions to be executed. Served in thirteen separate assignments . ;dx = remainder (modulus) like the above my 32 bit spec for this routine is mixed - the dividend is a unsigned 64 bit number where 1 - 0 1 (both 32 bits) and the divisor is a 32bit unsigned number. This way of addressing results in slower processing of data. The MOV instruction may have one of the following five forms , The MOV instruction causes ambiguity at times. Interrupt Flag (IF) It determines whether the external interrupts like keyboard entry, etc., are to be ignored or processed. Illinois Administrative Code, Title 77 - PUBLIC HEALTH, Part 615 - LOCAL HEALTH PROTECTION GRANT CODE. The following code snippet shows the use of the system call sys_exit , The following code snippet shows the use of the system call sys_write . I tried the code in the question (I used NASM so I replaced the, Same thing. This addressing mode uses the arithmetic operators to modify an address. This addressing mode utilizes the computer's ability of Segment:Offset addressing. The fundamental unit of computer storage is a bit; it could be ON (1) or OFF (0) and a group of 8 related bits makes a byte on most of the modern computers. It faults on overflow of the quotient. Probably a good idea to ask that as a new question (and link it from here. Note that 8-bit operand-size is special: the implicit inputs/outputs are in AH:AL (aka AX), not DL:AL. CX is known as the count register, as the ECX, CX registers store the loop count in iterative operations. . In this tutorial, we focus on Intel-32 processors like Pentium. For signed idiv, it gives you the remainder (not modulus) which can be negative: As we discussed about storing the values of the registers in the stack before using them for some use; it can be done in following way . When two doubleword values are multiplied, the multiplicand should be in EAX and the multiplier is a doubleword value stored in memory or in another register. Is there a proper earth ground point in this switch box? Why are elementwise additions much faster in separate loops than in a combined loop? Alternatively, you can store strings with a trailing sentinel character to delimit a string instead of storing the string length explicitly. How programs interface with OS, processor, and BIOS; How data is represented in memory and other external devices; How the processor accesses and executes instruction; How instructions access and process data; An IBM PC or any equivalent compatible computer. This value is stored in the EBX register. The NUM_1 is divided by NUM_2 which gives a quotient of C1 and remainder of 01. Base Pointer (BP) The 16-bit BP register mainly helps in referencing the parameter variables passed to a subroutine. It is not clear whether you want to move a byte equivalent or word equivalent of the number 110. Also, PIC library code for their C compilers is free to look up and provides assembly code, as well. Put the file permissions in the ECX register. Architectures Software Developers Manuals. Basically, hexadecimal number system represents a binary data by dividing each byte in half and expressing the value of each half-byte. This directive is similar to the #define in C. For example, you may define the constant PTR as . The AND instruction is used for supporting logical expressions by performing bitwise AND operation. Put the system call sys_lseek () number 19, in the EAX register. Is a PhD visitor considered as a visiting scholar? The source operand is assumed to be at DS:SI (or ESI) and the destination operand at ES:DI (or EDI) in memory. SCAS This instruction compares the contents of a register (AL, AX or EAX) with the contents of an item in memory. If you don't care too much about performance and want to use the straightforward way, you can use either DIV or IDIV. Type the above code using a text editor and save it as hello.asm. There are two sets of index pointers . If the operand is a 16 bit register than the number in DX:AX is divided by the operand and the answer is stored in AX and remainder in DX . Transfer of control may be forward, to execute a new set of instructions or backward, to re-execute the same steps. There are numerous conditional jump instructions depending upon the condition and data. Not the answer you're looking for? The syntax of the EQU directive is as follows , You can then use this constant value in your code, like , The operand of an EQU statement can be an expression . 14 CBW, CWD, CDQ Instructions The CBW, CWD, and CDQ instructions provide important sign-extension operations: CBW (convert byte to word) extends AL into AH CWD (convert word to doubleword) extends AX into DX CDQ (convert doubleword to quadword) extends EAX into EDX I have started to learn assembly programming in NASM, I want to write a basic arithmetic program. Find the remainder when N is divided by 4 using Bitwise AND operator Difficulty Level : Basic Last Updated : 25 Sep, 2022 Read Discuss Courses Practice Video Given a number N, the task is to find the remainder when N is divided by 4 using Bitwise AND operator. All pseudo-ops start with a period. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. CMPS This instruction compares two data items in memory. . Both the operands in MOV operation should be of same size, The value of source operand remains unchanged. C#. The system call returns the actual number of bytes written in the EAX register, in case of error, the error code is in the EAX register. The remainder of the line specifies the libraries and object files to be linked. Not the answer you're looking for? I am using MASM assembler. To reference a register as an operand, use the syntax To learn more, see our tips on writing great answers. Recursion could be observed in numerous mathematical algorithms. Each of the above instruction has a byte, word, and doubleword version, and string instructions can be repeated by using a repetition prefix. Well documented and you will get lots of information on net. It is implemented as a 'stack' data structure. For example . rev2023.3.3.43278. This flag is set according to the sign of a data item following the arithmetic operation. What assembler are you using? Be able to solve a conditional statement using branches. Difficulties with estimation of epsilon-delta limit proof, Identify those arcade games from a 1983 Brazilian music video, Recovering from a blunder I made while emailing a professor. It repeats the operation while the zero flag indicates not equal/zero. shr cnt, dest. For div, using a dividend with high_half < divisor is safe. How can I check before my flight that the cloud separation requirements in VFR flight rules are met? Example Hexadecimal number FAD8 is equivalent to binary - 1111 1010 1101 1000, The following table illustrates four simple rules for binary addition . An immediate operand has a constant value or an expression. The following example divides 8 with 2. For displaying a string of characters, you need the following sequence of instructions . DIV r32 divides a 64-bit number in EDX:EAX by a 32-bit operand (in any register or memory) and stores the quotient in EAX and the remainder in EDX. my bp for example is 9E8, then should i use bx instead of bl? The format for the DIV/IDIV instruction , The dividend is in an accumulator. Where, variable-name is the identifier for each storage space. You can see from the contents of register AX that AH contains the remainder and AL stores the quotient. The AND operation can be used for clearing one or more bits. There are four instructions for processing numbers in ASCII representation . Health Licensing Office Laws (unofficial user friendly copy) - ORS 676. Each define directive has a related reserve directive. Put the offset value in the ECX register. Some instructions do not require an operand, whereas some other instructions may require one, two, or three operands. Depending upon the instruction, the register may be the first operand, the second operand or both. Assembly language statements are entered one statement per line. It adds the values in the array and displays the sum 9 . The system call returns the file descriptor of the created file in the EAX register, in case of error, the error code is in the EAX register. How to match a specific column position till the end of line? For example, say the BL register contains 0011 1010. The remainder has the same sign as the dividend; the absolute value of the remainder is always less than the absolute value of the divisor. Rules (iii) and (iv) show a carry of a 1-bit into the next left position. 2 Answers Sorted by: 5 You can't use al as divisor, because the command div assumes ax to be the dividend. A block of timber under the foot jack is handy to ge If the parity is even, the system assumes that there had been a parity error (though rare), which might have been caused due to hardware fault or electrical disturbance. It can be used to reserve as well as initialize one or more bytes. REP executes the instruction, decreases CX by 1, and checks whether CX is zero. The XOR instruction implements the bitwise XOR operation. Look at the following simple program to understand the use of registers in assembly programming. Why does GCC use multiplication by a strange number in implementing integer division? In this addressing mode, a register contains the operand. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Asking for help, clarification, or responding to other answers. x86 idiv does indeed fault in this case. The DEBUG program we used sets the trap flag, so we could step through the execution one instruction at a time. Washington, District of Columbia, United States. The processor supports the following data sizes . div and idiv will fault if the quotient doesn't fit into one register (AL / AX / EAX / RAX, the same width as the dividend). This directive allows redefinition. What's the difference between mod and remainder? Do roots of these polynomials approach the negative of the Euler-Mascheroni constant? On which platforms does integer divide by zero trigger a floating point exception? Connect and share knowledge within a single location that is structured and easy to search. The processor stores data in reverse-byte sequence, i.e., a low-order byte is stored in a low memory address and a high-order byte in high memory address. The syntax for the MUL/IMUL instructions is as follows , Multiplicand in both cases will be in an accumulator, depending upon the size of the multiplicand and the multiplier and the generated product is also stored in two registers depending upon the size of the operands. This is probably why they chose remainder=EDX quotient=EAX instead of the other way around. Every number system uses positional notation, i.e., each position in which a digit is written has a different positional value. Code segment It is represented by .text section. Following is the syntax to define a procedure , The procedure is called from another function by using the CALL instruction. Generally, the source data remains unaltered after the operation. The math equation is simple, but it's still . The OR operation can be used for setting one or more bits. How to perform an integer division, and separately get the remainder, in JavaScript? It consists of three continuous steps . The product generated is stored in the EDX:EAX registers, i.e., the high order 32 bits gets stored in the EDX register and the low order 32-bits are stored in the EAX register. Making statements based on opinion; back them up with references or personal experience. on the screen. Many instructions involve comparisons and mathematical calculations and change the status of the flags and some other conditional instructions test the value of these status flags to take the control flow to other location. It does not disturb the destination or source operands. The ADD and SUB instructions have the following syntax , The ADD/SUB instruction can take place between . It also stores the contents of last bit of a shift or rotate operation. The variables are double-digit variables. Example So, if the processor brings the value 0725H from register to memory, it will transfer 25 first to the lower memory address and 07 to the next memory address. A place where magic is studied and practiced? As complete 32-bit data registers: EAX, EBX, ECX, EDX. The address in SS register is combined with the offset in BP to get the location of the parameter. However, machine language is too obscure and complex for using in software development. When two one-word values are multiplied . Thanks for contributing an answer to Stack Overflow! Find centralized, trusted content and collaborate around the technologies you use most. IP in association with the CS register (as CS:IP) gives the complete address of the current instruction in the code segment. Beware signed integers, though! Using Kolmogorov complexity to measure difficulty of problems? We will uses the standard AT&T syntax for writing x86 assembly code. You can't use al as divisor, because the command div assumes ax to be the dividend. Each family of processors has its own set of instructions for handling various operations such as getting input from keyboard, displaying information on screen and performing various other jobs. Understand the load and store instructions and data sizes. BP can also be combined with DI and SI as base register for special addressing. An assembly program can be divided into three sections . They are . When an instruction requires two operands, the first operand is generally the destination, which contains data in a register or memory location and the second operand is the source. In the following example , $ points to the byte after the last character of the string variable msg. The variable length strings can have as many characters as required. ), @LetsGoBrandon Modulo is similar to division in that it is undefined for. Jan 1999 - Apr 202223 years 4 months. It may contain any printable character including blank. What is a word for the arcane equivalent of a monastery? Faifi is spoken by about 50,000. The JMP instruction provides a label name where the flow of control is transferred immediately. For example, consider the case of calculating the factorial of a number. For example, the decimal value 1234 is stored as , Where, 31H is ASCII value for 1, 32H is ASCII value for 2, and so on. If your modulus / divisor is a known constant, and you care about performance, see this and this. The high 32 bits are placed in a register called HI.The low 32 bits are placed in a register called LO.You only need to read LO if you know your result fits into the Lower 32-bits.. To access the HI and LO registers, which are 2 additional registers beyond . The syntax for storage allocation statement for initialized data is . In direct recursion, the procedure calls itself and in indirect recursion, the first procedure calls a second procedure, which in turn calls the first procedure. Cortex-M4 has command to divide numbers, but have no command to get a remainder. So far, we have converted this input data in ASCII form to binary for arithmetic calculations and converted the result back to binary. The following example uses the AAS instruction to demonstrate the concept , There are two types of BCD representation , In unpacked BCD representation, each byte stores the binary equivalent of a decimal digit. These registers take the consecutive arguments, starting with the EBX register. So, each time you need to display on screen, you need to save these registers on the stack, invoke INT 80H and then restore the original value of the registers from the stack. Or for 3 fractional (decimal) digits, just compute 10^3 * remainder . In the light of the above discussion, we can specify various memory segments as . This call allocates memory right behind the application image in the memory. The syntax for declaring text section is , Assembly language comment begins with a semicolon (;). To convert a binary number to its hexadecimal equivalent, break it into groups of 4 consecutive groups each, starting from the right, and write those groups over the corresponding digits of the hexadecimal number. How to handle a hobby that makes income in US. These sections represent various memory segments as well. Stack Pointer (SP) The 16-bit SP register provides the offset value within the program stack. To install NASM, take the following steps . Why does integer division by -1 (negative one) result in FPE? To execute a program, the system copies it from the external device into the internal memory. End of the procedure is indicated by a return statement. In direct addressing mode, the offset value is specified directly as part of the instruction, usually indicated by the variable name. It returns 0, if both the bits are zero. There are three categories of pointer registers . This is 8 bit division, so yes the remainder will be stored in ah. We have observed that, some instructions like IMUL, IDIV, INT, etc., need some of the information to be stored in some particular registers and even return values in some specific register(s). sys_write and sys_exit, for writing into the screen and exiting from the program, respectively. The format for the DIV/IDIV instruction , The dividend is in an accumulator. Stack This segment contains data values passed to functions and procedures within the program. This is an example for dividing bp by 7 mov ax,bp // ax is the dividend mov bl,7 // prepare divisor div bl // divide ax by bl This is 8 bit division, so yes the remainder will be stored in ah. For unsigned, remainder and modulus are the same thing. In assembly programming, a program needs to access the memory locations. The symbolic address of the first number will be NUMBERS and that of the second number will be NUMBERS + 2 and so on. There are 32 registers that we commonly use. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. rev2023.3.3.43278. A macro is a sequence of instructions, assigned by a name and could be used anywhere in the program. If the bits from the operands are same (both 0 or both 1), the resultant bit is cleared to 0. Example Perform a 16-bit signed divide of the DX:AX register by the contents of the effective address (addressed by the EDI register plus an offset of 4) and store the quotient in the AX register divw 4(%edi) The difference between the phonemes /p/ and /b/ in Japanese. It stops when the ZF indicates equal/zero or when CX is decremented to zero. Hence the output is 2. Put the pointer to the input buffer in the ECX register. The text section is used for keeping the actual code. You can download it from various web sources. How do I align things in the following tabular environment? A place where magic is studied and practiced? Click the card to flip Definition 1 / 30 true Click the card to flip Flashcards Learn Test Match Created by dangle0905 Terms in this set (30) Why should EDX be 0 before using the DIV instruction? Recommended: Please try your approach on {IDE . The result is in al. m 9.5 \mathrm {~m} 9.5 m. Verified answer. AL = AL / operand, AH = remainder (modulus). Transfer of control may be forward, to execute a new set of instructions or backward, to re-execute the same steps. Processor uses the little-endian byte ordering. The following example multiplies 3 with 2, and displays the result . The result is usually returned in the EAX register. And what output are you actually getting? Analogically, instead of using MUL or DIV with powers of two, bit-shifting is the way to go. It works on a single operand that can be either in a register or in memory. This version is simpler to install, just double-click the RPM file. Both the instructions can work with 8-bit, 16-bit or 32-bit operands. \$\endgroup\$ - Stack Segment It contains data and return addresses of procedures or subroutines. We have already discussed that the data definition directives to the assembler are used for allocating storage for variables. Use STD (Set Direction Flag, DF = 1) to make the operation right to left. Segment address (or offset) - starting address of a memory segment with the offset value. Otherwise, you will see just nasm:, then you need to install NASM. To speed up the processor operations, the processor includes some internal memory storage locations, called registers.