Which is faster multiply or divide

Quote: Original post by Carolina What I know for sure is that x86 Assembly language provides these operations in some ways so things get optimized Not always true. I haven't kept up with the timings on the latest chips, but all the way up to the it was actually faster to do "dec cx, jnz label". Not only was it faster, but it made it possible to use other registers than CX to hold a loop counter. Ah, the balancing act of performance, vs.

I'm glad I don't make CPUs. Intel ASM is a horrible kludge of ancient technology that they've miraculously been able to keep going.

While a new processor design could beat it in performance, not a by a huge enough margin for everyone to give up backwards compatibility, experience, etc. Conner McCloud Quote: Original post by brandonman if I'm not mistaken, I read in one of my books that computers don't divide, they can only add, so none of them would be quicker according to taht You are mistaken.

This topic is closed to new replies. Nagle So what's going on with the "Metaverse"? GDNet Lounge. How enemy AI decide to dodge or block from player's melee attack? Artificial Intelligence. Neural networks from beggining Artificial Intelligence. GeneralJist Am I a producer? Games Career Development. TimCS 0. The smallest possible value is given by Algorithm 2 in our paper and it involves a bit of mathematics note: the notation in my blog post differs from the paper, N becomes F. Follow-up blog post : More fun with fast remainders when the divisor is a constant where I discuss finer points.

View all posts by Daniel Lemire. I ageee. Its great to test to the approach, but realistically most people writing code will not use your library only because they dont know it exists…. It would be better if just a normal part of the compile process in the compiler itself. This is applicable to JavaScript. Integer arithmetic in JavaScript is tricky so you would need to focus on a specific problem.

All numbers in JS are floats under the hood so the raw bits are not going to act the same as ints. Numbers in JavaScript are stored as doubles, and thus cannot exactly represent an integer over 53 bits. Additionally, the bitwise operators all convert the operands to bit signed integers before performing the operation. You are doubly unable to do bit shifts in JavaScript. The most likely answer is that JavaScript does not use 64 bit integer numbers.

It uses 64 bit floating point numbers which happen to look like integers for most development purposes. It is a similar idea regarding the divisibility test but it does not look the same to me. Also the answer seems to differentiate between odd and even integers, we do not. Great article and paper! Can yo perhaps share some timings as well, in addition to the bits case? You do not need bit intermediate computations, bit is enough. However, the engineering gets more complicated if you are to deal with overflows properly.

We are inviting people to pursue the research. We do not claim to have written the last word on this. If you are interested in pursuing the research and want to chat, do get in touch with us. Of course, these fizzbuzz tests do not use the division instruction. The division instruction would be slower.

However, it would be less terrible than on skylake processors. Of course, division and support for signed integers would be desirable as well, but for my purposes, a fast bit mod is all I need. I did not write these functions not in the current form. I think that the contributor who rewrote them meant to make them more transparent.

For example this libdivide issue could be finally updated looks like someone got to it since I first ran across it. This means that on a typical bit machine only divisors are supported, and on bit only bit divisors are supported. A commenter on this blog post has reported an application of the mathematical result to bit unsigned division on bit processors.

An additional insight is that you can avoid the extra work related to avoiding overflows by just using wider registers. However, the earlier work and this one primarily focus on the efficient implementation of these methods on real hardware. In that domain, the general target is to implement W-bit division on W-bit machines, and a large amount of the complexity in analysis and much of the runtime cost comes as a result of the difficulty of doing that.

I cannot dictate what is important or interesting to you. But maybe you agree that more than one thing can be interesting at once. As far as we know, nobody worked out the mathematics for the direct computation of the remainder. Authors simply ignored the issue. Completing the mathematical framework was important, I think. It might be. It is certainly worth exploring. It was often faster than other alternatives, but also generally slower than the direct approach.

Because it was unexciting, it is not reported in the published paper even if it appears in our logs and public code. What I mean is that at a high level what makes this whole thing interesting to me, to you, to almost everyone, I think in the first place is that it is potentially more efficient than any existing approach.

Once that is established, then the math becomes very important indeed to establish the correctness and to understand the limits. Thomas: I tend to go easy on newbies. We all make or at least made mistakes at one point or another, and getting scorched for it doesn't make anyone feel welcome. Helping less experienced people is a good thing, and StackOverflow is very good at that. For x86, see agner. Both are only 1 uop, so can overlap well with other operations.

Intel Skylake has a very heavily pipelined FP div unit throughput of one double result per 4 cycles. Show 1 more comment. Edit: AMD's optimisation guide for Family 15h processors, provide figures for fdiv and fmul are 42 and 6 respectively.

From memory, Intel's figures aren't that far off. Elis Byberi 1, 1 1 gold badge 10 10 silver badges 19 19 bronze badges. Mats Petersson Mats Petersson k 13 13 gold badges silver badges bronze badges. Please tell me so I can learn! I didn't downvote, have no idea why someone else did, but I hope you don't mind that I corrected your statement about 0.

It's not quite clear what you mean in the second paragraph the parenthesis is never closed, and the sentence kind of trails off. But as has been pointed out in the comments to other answers, the compiler typically won't convert divisions to multiplies when dealing with floating-point code.

Jalf: yes, I have clarified the second paragraph a little bit. Add a comment. David Heffernan k 40 40 gold badges silver badges bronze badges. This is a situation where we cannot rely on the optimizer, if we ask about cases other than single example in the question.

Division by a power of two and multiplication by the inverse are equivalent in binary floating-point, but divisions by other factors have no equivalent multiplication, because the reciprocal cannot be exactly represented. This prohibits the optimizer from making the transformation. Thus, programmers should be aware of this and should favor multiplication if they know the rounding error in the inverse is acceptable. EricPostpischil: Does it "help" to give flags for "use fast math" in cases where we don't care too much about precision?

Say, forexample in case of 3d games, you'd expect that the last couple of bits of floating point precision doesn't matter. The Overflow Blog. Podcast Explaining the semiconductor shortage, and how it might end. Does ES6 make JavaScript frameworks obsolete? Featured on Meta. Now live: A fully responsive profile. Linked