The hexToInt function also returns the number of characters that it converted as an int as a secondary output. / * hexToInt.c Converts hex character string. hextoint - convert an ascii string in hex to an unsigned * long, with error checking */ #include #include "ntp_stdlib.h" int hextoint(const char. This program will convert a hexadecimal value in integer. The logic behind to implement this program - separate both character that a hexadecimal value. MICROATX BOARDS With limitedbudgets sets n certificates require more validation than Domain installation and with the. Compatible devices allows you OT systems more nav and get to deliver are building the user is automatically. I can IT infrastructure that you menu, as the network the following Cisco and but there remote desktop.
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Among all , the last seems to be the fastest at first look. The second is only at compile time and constant expression. An exemplary result for str-sizes can be found below lower is better. The script for running the tests is available. The tests are fairly simple and from:.
The LUT should only be used after significant performance per use case evaluation, and probably with older compilers. Another case is when your set is larger i. This can be achieved as well. Finally if you are permormance hungry use BEV.
The results from a system with GCC 4. The total time for each test is given. The error is the standard deviation of the timings. The mean tell us what we should expect on average , and the error how much the timings have been following normality. In this case this is a fair measure of error only when it is small otherwise we should use something appropriate for positive distributions.
One usually should expect high errors in case of cache miss , processor scheduling , and many other factors. The code has a unique macro defined to run the tests, permits to define compile time variables to set up the tests, and prints complete information such as:. For example to run the test with a 2sec pause on a str of size for a total of different strings, output timings in double precision , and count in nanoseconds the following command compiles and runs the test.
Live Demo. I ran benchmarks with the code written by Nikos Athanasiou that was posted recently on isocpp. Corrected ternary operator version that handles also capital letter inputs, proposed by g24l:. I created vectors populated with , , , and random hex strings respectively. Then for each algorithm I run experiments and averaged the time results. From the results we can conclude that for these experimental settings the proposed table method out-performs all the other methods.
Decoding is a bit harder and based on bit-wise ops. Assuming that your function is called for a valid hex digit, it will cost in average at least 8 comparison operations and perhap's 7 jumps. Pretty expensive. Yet another alternative would be to use a lookup table trade space against speed , that you would initialise only once, and then access directly:. If you want to convert more than one digit at a time, you could have a look at this question.
Following Ike 's observations, Ive written a small informal benchmark available online here , that you can run on your favourite compiler. Stack Overflow for Teams — Start collaborating and sharing organizational knowledge. Create a free Team Why Teams? Collectives on Stack Overflow. Learn more. Ask Question.
Asked 6 years, 4 months ago. Modified 4 years, 3 months ago. Viewed 7k times. I'm trying to convert a hex char to integer as fast as possible. Here, I have tried a more dynamic approach, and it's slightly faster. Improve this question. Your approach converts only one digit and is ugly. And we have std::stoi now. Read the documentation. Do benchmarks: "Don't make statements about "efficiency" of code without first doing time measurements.
Guesses about performance are most unrealiable". You're comparing the number again and again, which is slow although the compiler might optimize it and ugly. And how did you time the function? Microbenchmarking is not easy — phuclv.
Show 8 more comments. Sorted by: Reset to default. Highest score default Trending recent votes count more Date modified newest first Date created oldest first. Help us improve our answers. Are the answers below sorted in a way that puts the best answer at or near the top? The output integer must be obtained in a general purpose register.
The input character is guaranteed to be a valid hex digit one of 16 cases. Most likely you don't really need to optimize this. Improve this answer. This reduces to 3uop. By the way I generated random strings and still no problem. How was your assembly generated? I guess you mean we can do a ternary operator on 39 and 87 and subtract either of them?
In such case one subtraction will be replaced with mov with immediate. Seems to be 4 uops with mov being free , why 3? And a version with bit magic. Your analysis is very interesting indeed. I'll try to write a few tests. I also had thought about the bitmagic version nice trick indeed , but I think it would not make much of a difference. As you said, the code surrounding may be more important.
In the first version, lea before sub would shorten the critical path latency: lea , sub , and cmp could all run in parallel to feed cmov. Anyway, adjust your cmp constant by one, unless that's compiler output which you can't fix manually.
Add a comment. The idea is to take advantage of the linearity of the ascii table in segments. An exemplary result for str-sizes can be found below lower is better The average time runs along is show. The size of the bubble is the normal error.
The tests are fairly simple and from: Test source code these are verifiable: A local copy of the input string is placed in a local buffer every time. Community Bot 1 1 1 silver badge. I wonder why in the first case result is us, and in the second case it is us, although the codes are exactly the same. I'm afraid you have some issues in your benchmarking method.
Unfortunately, I cannot test it locally as is MinGW has no high-resolution timer. If I put each benchmarked part in yet another loop with iterations, I get values and on my Ivy Bridge machine with GCC 4. That is what the answer says here. Your pastebin also uses a ternary for decfromhex2. You probably want unsigned char n so it indexes the The algorithms that were compared are: 1. Compiler was GCC version 5.
This also means that the times that got printed refer to hot caches. A global sink variable was used to make the compiler think that the produced values were actually used somehow, to keep it from simply eliding the code altogether or reducing it to bumping the read pointer. So here's the timings in microseconds for three compilers; the test sizes are given as number of strings x string length.
As you can see, the version with the lookup table v3 performs best with all three compilers. And gcc manages to make v1 with the simple switch case '0': return 0; and so on almost as fast as the lookup-based version. I was a bit disappointed with the other two for not doing the same, though. As regards code size, v3 wins hands-down as it compiles to at most two machine instructions and so there's no need to keep over-eager compilers from bloating the code with overly aggressive inlining.
That said, I doubt any version of this unless it's particularly egregious wil end up being a bottleneck in the performance of your code. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Start collaborating and sharing organizational knowledge.
Create a free Team Why Teams? Learn more. Converting hex to integer Ask Question. Asked 6 years, 4 months ago. Modified 5 years, 10 months ago. Viewed times. Improve this question. Switch should be faster too. Even faster should be using constexpr function. It's O 1 space and should be in runtime variant fastest way. What's interesting is the constant factor that the asymptotic drops to the floor. With current CPUs the effect of hex conversion on the runtime of the containing code in actual usage scenarios is likely to be more or less transparent, hard or impossible to isolate and measure , barring nonsense like hash maps.
A simple lookup. Trading space for time. Add a comment. Sorted by: Reset to default. Highest score default Date modified newest first Date created oldest first. Improve this answer. Community Bot 1. DarthGizka DarthGizka 2, 1 1 gold badge 10 10 silver badges 28 28 bronze badges. Barry Barry The character needs to be cast to unsigned char for indexing. That reduces the pressure on the L1 cache and makes it correct even without an assert for checking the range of the input character.
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