This is because of the costly conversion from a floating point to an integer for multiplication, and then converting the multiplied integer back into a floating point. The reason imul exists is because it is faster in only one so far circumstance: AsmJS. Multiplying two numbers stored internally as integers which is only possible with AsmJS with imul is the only potential circumstance where Math.
Related Topics. Standard built-in objects Math Properties Math. E Math.
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Chrome Full support Edge Full support Firefox Full support IE No support No. Opera Full support Safari Full support 7. Chrome Android Full support Firefox Android Full support Opera Android Full support Safari iOS Full support 7. Samsung Internet Android Full support 1.The INC instruction is used for incrementing an operand by one. It works on a single operand that can be either in a register or in memory. The DEC instruction is used for decrementing an operand by one.
The following example will ask two digits from the user, store the digits in the EAX and EBX register, respectively, add the values, store the result in a memory location ' res ' and finally display the result. There are two instructions for multiplying binary data. Both instructions affect the Carry and Overflow flag. 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.
The multiplicand is in the AL register, and the multiplier is a byte in the memory or in another register. The product is in AX. High-order 8 bits of the product is stored in AH and the low-order 8 bits are stored in AL. The multiplicand should be in the AX register, and the multiplier is a word in memory or another register. The resultant product is a doubleword, which will need two registers.
The high-order leftmost portion gets stored in DX and the lower-order rightmost portion gets stored in AX. 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. The division operation generates two elements - a quotient and a remainder. In case of multiplication, overflow does not occur because double-length registers are used to keep the product.
However, in case of division, overflow may occur. The processor generates an interrupt if overflow occurs. The dividend is in an accumulator. Both the instructions can work with 8-bit, bit or bit operands. The operation affects all six status flags.
The dividend is assumed to be in the AX register 16 bits. After division, the quotient goes to the AL register and the remainder goes to the AH register. The dividend is assumed to be 32 bits long and in the DX:AX registers. The high-order 16 bits are in DX and the low-order 16 bits are in AX. After division, the bit quotient goes to the AX register and the bit remainder goes to the DX register.
The following example divides 8 with 2.
Assembly - Arithmetic Instructions
The dividend 8 is stored in the bit AX register and the divisor 2 is stored in the 8-bit BL register. Assembly - Arithmetic Instructions Advertisements. Previous Page. Next Page.I did what I was supposed to do. It's not fair. DeviantArt: AlwaysLuminescent. Email: luminousterror74 gmail.
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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I've written a very basic C-function called "multby22", which does exactly what its name implies: it takes a long and returns that long multiplied by I know it's a pointless function but I wrote it to try and help me with x86 assembly.
When I complied the program and ran "objdump" on the executable, I found the disassembled code for "multby22" to be the following:. I understand that "imul" is for integer multiplication, but I have been unable to find anything that helps me with this syntax!
The closest I have found is:. In the assembly I generated, the 1st argument is a constant! You found the right instruction. The destination register is on the right. If you are trying to compare instructions against the documentation, you should probably look into a disassembler that can output Intel syntax disassembly. The compiler writes it in hex notation there. So the first will be multiplicated with the second and stored into the third. Learn more. Asked 7 years, 8 months ago.
Active 4 years, 10 months ago. Viewed 7k times. The closest I have found is: imul [reg] [reg] [const] Michael Petch Thanizer Thanizer 1 1 gold badge 6 6 silver badges 20 20 bronze badges. Read up on the Intel vs. And if you compile with a bit of optimization, most of those extra instrucitons will go away. Your code doesn't need a stackframe. Highly likely, the multiply by 22 will also be turned into a sequence of multiply by 5, then multiply by 2, add original value and multiply by 2.
Which I think will be three instructions - which together is faster than a mul instruction. Active Oldest Votes. Carl Norum Carl Norum k 25 25 gold badges silver badges bronze badges. Tom Tom 9 9 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
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Related Hot Network Questions.The following table provides a list of xAssembler mnemonics, that is not complete. Most of them can be found, for others see at www. The high order nibble is zeroed. Multiplies AH by 10 and the adds result into AL. Sets AH to zero. This instruction is also known to have an undocumented behavior. The high order nibble of each byte must be zeroed before using this instruction. High order nibble is zeroed. If CF is set, a 1 is added to the destination.
Both operands are binary. Otherwise the Zero Flag is cleared. Interrupt 5 occurs if the source value is less than or higher than the source. Sets ZF if a bit is found set and loads the destination with an index to first set bit. Clears ZF is no bits are found set. Result left in destination register is undefined if the operand is a 16 bit register.
Code continues with execution at CS:IP. NMI's and software interrupts are not inhibited. This is a privileged operation and is generally used only by operating system code. Flags can subsequently be checked for conditions. Updates flags based on the subtraction and the index registers E SI and E DI are incremented or decremented depending on the state of the Direction Flag.
The REP prefixes can be used to process entire data items. If equal the "dest" is loaded with "src", otherwise the accumulator is loaded with "dest". Contents of AL are changed to a pair of packed decimal digits.
If the source divisor is a byte value then AX is divided by "src" and the quotient is placed in AL and the remainder in AH. Operand "locals" specifies the amount of storage to be allocated on the stack. If the source operand is a byte value, it is multiplied by AL and the result stored in AX.
Other variations of this instruction allow specification of source and destination registers as well as a third immediate factor. If the port number is in the range of it can be specified as an immediate, otherwise the port number must be specified in DX. E DI is adjusted by the size of the operand and increased if the Direction Flag is cleared and decreased if the Direction Flag is set.
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Actions Shares. Embeds 0 No embeds. No notes for slide. Chapter 8 The stack and introduction to procedures 3. C Exchange the TOP two words on the stack. You may use AX, BX 4.
Question 7: Procedures are supposed to return the stack to the calling program in the same condition that they received it. However it may be useful to have procedures that alter the stack. Answer: 5. Chapter 9 Multiplication and division instructions 6. Or tell if overflow occurs.