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  • Find max integer size that a floating point type can handle without loss of precision

    - by Checkers
    Double has range more than a 64-bit integer, but its precision is less dues to its representation (since double is 64-bit as well, it can't fit more actual values). So, when representing larger integers, you start to lose precision in the integer part. #include <boost/cstdint.hpp> #include <limits> template<typename T, typename TFloat> void maxint_to_double() { T i = std::numeric_limits<T>::max(); TFloat d = i; std::cout << std::fixed << i << std::endl << d << std::endl; } int main() { maxint_to_double<int, double>(); maxint_to_double<boost::intmax_t, double>(); maxint_to_double<int, float>(); return 0; } This prints: 2147483647 2147483647.000000 9223372036854775807 9223372036854775800.000000 2147483647 2147483648.000000 Note how max int can fit into a double without loss of precision and boost::intmax_t (64-bit in this case) cannot. float can't even hold an int. Now, the question: is there a way in C++ to check if the entire range of a given integer type can fit into a loating point type without loss of precision? Preferably, it would be a compile-time check that can be used in a static assertion, and would not involve enumerating the constants the compiler should know or can compute.

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  • Work Time Start / Stop Tracking Software

    - by Shaharyar
    Is there a software that allows you to keep track of someones working time digitally? We are growing to an extent where we work remotely and we would like to have fixed working times. All it should do is kind of register when someone starts working (i.e. someone needs to login somewhere or set a flag.. really it could be anything) Do you have any ideas?

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  • BigDecimal precision not persisted with javax.persistence annotations

    - by dkaczynski
    I am using the javax.persistence API and Hibernate to create annotations and persist entities and their attributes in an Oracle 11g Express database. I have the following attribute in an entity: @Column(precision = 12, scale = 9) private BigDecimal weightedScore; The goal is to persist a decimal value with a maximum of 12 digits and a maximum of 9 of those digits to the right of the decimal place. After calculating the weightedScore, the result is 0.1234, but once I commit the entity with the Oracle database, the value displays as 0.12. I can see this by either by using an EntityManager object to query the entry or by viewing it directly in the Oracle Application Express (Apex) interface in a web browser. How should I annotate my BigDecimal attribute so that the precision is persisted correctly? Note: We use an in-memory HSQL database to run our unit tests, and it does not experience the issue with the lack of precision, with or without the @Column annotation.

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  • negative precision values in ostream

    - by daz-fuller
    This is more of a question of curiosity but does anyone know how negative precision values are handled in C++? For example: double pi = 3.14159265; cout.precision(-10); cout.setf(ios::fixed, ios::floatfield); cout << pi << endl; I've tried this out and using GCC and it seems that the precision value is ignored but I was curious if there is some official line on what happens in this situation.

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  • Unable to sync time using `ntpdate`, error: "no server suitable for synchronization found"

    - by William Ting
    My ntp.conf file: user@pc[0][07:37:40]:/etc$ cat /etc/ntp.conf idriftfile /var/lib/ntp/ntp.drift server 0.pool.ntp.org server 1.pool.ntp.org server 2.pool.ntp.org server pool.ntp.org Command output: user@pc[0][07:37:24]:/etc$ sudo ntpdate -dv pool.ntp.org 18 Jun 07:37:35 ntpdate[10737]: ntpdate [email protected] Tue Apr 19 07:15:05 UTC 2011 (1) Looking for host pool.ntp.org and service ntp host found : conquest.kjsl.com transmit(198.137.202.16) transmit(216.45.57.38) transmit(64.6.144.6) transmit(198.137.202.16) transmit(216.45.57.38) transmit(64.6.144.6) transmit(198.137.202.16) transmit(216.45.57.38) transmit(64.6.144.6) transmit(198.137.202.16) transmit(216.45.57.38) transmit(64.6.144.6) transmit(198.137.202.16) transmit(216.45.57.38) transmit(64.6.144.6) 198.137.202.16: Server dropped: no data 216.45.57.38: Server dropped: no data 64.6.144.6: Server dropped: no data server 198.137.202.16, port 123 stratum 0, precision 0, leap 00, trust 000 refid [198.137.202.16], delay 0.00000, dispersion 64.00000 transmitted 4, in filter 4 reference time: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 originate timestamp: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 transmit timestamp: d1a71a93.1f16c1e3 Sat, Jun 18 2011 7:37:39.121 filter delay: 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 filter offset: 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 delay 0.00000, dispersion 64.00000 offset 0.000000 server 216.45.57.38, port 123 stratum 0, precision 0, leap 00, trust 000 refid [216.45.57.38], delay 0.00000, dispersion 64.00000 transmitted 4, in filter 4 reference time: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 originate timestamp: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 transmit timestamp: d1a71a93.524a05dd Sat, Jun 18 2011 7:37:39.321 filter delay: 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 filter offset: 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 delay 0.00000, dispersion 64.00000 offset 0.000000 server 64.6.144.6, port 123 stratum 0, precision 0, leap 00, trust 000 refid [64.6.144.6], delay 0.00000, dispersion 64.00000 transmitted 4, in filter 4 reference time: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 transmitted 4, in filter 4 reference time: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 originate timestamp: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 transmit timestamp: d1a71a93.524a05dd Sat, Jun 18 2011 7:37:39.321 filter delay: 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 filter offset: 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 delay 0.00000, dispersion 64.00000 offset 0.000000 server 64.6.144.6, port 123 stratum 0, precision 0, leap 00, trust 000 refid [64.6.144.6], delay 0.00000, dispersion 64.00000 transmitted 4, in filter 4 reference time: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 originate timestamp: 00000000.00000000 Thu, Feb 7 2036 0:28:16.000 transmit timestamp: d1a71a93.857c6fbd Sat, Jun 18 2011 7:37:39.521 filter delay: 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 filter offset: 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 delay 0.00000, dispersion 64.00000 offset 0.000000 18 Jun 07:37:40 ntpdate[10737]: no server suitable for synchronization found

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  • How to make a system time-zone sensitive?

    - by Jerry Dodge
    I need to implement time zones in a very large and old Delphi system, where there's a central SQL Server database and possibly hundreds of client installations around the world in different time zones. The application already interacts with the database by only using the date/time of the database server. So, all the time stamps saved in both the database and on the client machines are the date/time of the database server when it happened, never the time of the client machine. So, when a client is about to display the date/time of something (such as a transaction) which is coming from this database, it needs to show the date/time converted to the local time zone. This is where I get lost. I would naturally assume there should be something in SQL to recognize the time zone and convert a DateTime field dynamically. I'm not sure if such a thing exists though. If so, that would be perfect, but if not, I need to figure out another way. This Delphi system (multiple projects) utilizes the SQL Server database using ADO components, VCL data-aware controls, and QuickReports (using data sources). So, there's many places where the data goes directly from the database query to rendering on the screen, without any code to actually put this data on the screen. In the end, I need to know when and how should I get the properly converted time? There must be a standard method for this, and I'm hoping SQL Server 2008 R2 has this covered...

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  • Delphi - Frac function losing precision.

    - by PeteDaMeat
    I have a TDateTime variable which is assigned a value at runtime of 40510.416667. When I extract the time to a TTime type variable using the Frac function, it sets it to 0.41666666666. Why has it changed the precision of the value and is there a workround to retain the precision from the original value ie. to set it to 0.416667.

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  • x86-64 long double precision

    - by aaa
    hello. What is the actual precision of long double on Intel 64-bit platforms? is it 80 bits padded to 128 or actual 128 bit? if former, besides going gmp, is there another option to achieve true 128 precision?

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  • Time management and self improvement

    - by Filip
    I hope I can open a discussion on this topic as this is not a specific problem. It's a topic I hope to get some ideas on how people in similar situation as mine manage their time. OK, I'm a single developer on a software project for the last 6-8 months. The project I'm working on uses several technologies, mainly .net stuff: WPF, WF, NHibernate, WCF, MySql and other third party SDKs relevant for the project nature. My experience and knowledge vary, for example I have a lot of experience in WPF but much less in WCF. I work full time on the project and im curios on how other programmers which need to multi task in many areas manage their time. I'm a very applied type of person and prefer to code instead of doing research. I feel that doing research "might" slow down the progress of the project while I recognize that research and learning more in areas which I'm not so strong will ultimately make me more productive. How would you split up your daily time in productive coding time and time to and experiment, read blogs, go through tutorials etc. I would say that Im coding about 90%+ of my day and devoting some but very little time in research and acquiring new knowledge. Thanks for your replies. I think I will adopt a gradual transition to Dominics block parts. I kinda knew that coding was taking up way to much of my time but it feels good having a first version of the project completed and ready. With a few months of focused hard work behind me I hope to get more time to experiment and expand my knowlegde. Now I only hope my boss will cut me some slack and stop pressuring me for features...

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  • Daylight Saving Time Visualized

    - by Jason Fitzpatrick
    When you map out the Daylight Saving Time adjusted sunrise and sunset times over the course of the year, an interesting pattern emerges. Chart designer Germanium writes: I tried to come up with the reason for the daylight saving time change by just looking at the data for sunset and sunrise times. The figure represents sunset and sunrise times thought the year. It shows that the daylight saving time change marked by the lines (DLS) is keeping the sunrise time pretty much constant throughout the whole year, while making the sunset time change a lot. The spread of sunrise times as measured by the standard deviation is 42 minutes, which means that the sunrise time changes within that range the whole year, while the standard deviation for the sunset times is 1:30 hours. Whatever the argument for doing this is, it’s pretty clear that reason is to keep the sunrise time constant. You can read more about the controversial history of Daylight Saving Time here. Daylight Saving Time Explained [via Cool Infographics] 6 Ways Windows 8 Is More Secure Than Windows 7 HTG Explains: Why It’s Good That Your Computer’s RAM Is Full 10 Awesome Improvements For Desktop Users in Windows 8

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  • Time Tracking on an Agile Team

    - by Stephen.Walther
    What’s the best way to handle time-tracking on an Agile team? Your gut reaction to this question might be to resist any type of time-tracking at all. After all, one of the principles of the Agile Manifesto is “Individuals and interactions over processes and tools”.  Forcing the developers on your team to track the amount of time that they devote to completing stories or tasks might seem like useless bureaucratic red tape: an impediment to getting real work done. I completely understand this reaction. I’ve been required to use time-tracking software in the past to account for each hour of my workday. It made me feel like Fred Flintstone punching in at the quarry mine and not like a professional. Why You Really Do Need Time-Tracking There are, however, legitimate reasons to track time spent on stories even when you are a member of an Agile team.  First, if you are working with an outside client, you might need to track the number of hours spent on different stories for the purposes of billing. There might be no way to avoid time-tracking if you want to get paid. Second, the Product Owner needs to know when the work on a story has gone over the original time estimated for the story. The Product Owner is concerned with Return On Investment. If the team has gone massively overtime on a story, then the Product Owner has a legitimate reason to halt work on the story and reconsider the story’s business value. Finally, you might want to track how much time your team spends on different types of stories or tasks. For example, if your team is spending 75% of their time doing testing then you might need to bring in more testers. Or, if 10% of your team’s time is expended performing a software build at the end of each iteration then it is time to consider better ways of automating the build process. Time-Tracking in SonicAgile For these reasons, we added time-tracking as a feature to SonicAgile which is our free Agile Project Management tool. We were heavily influenced by Jeff Sutherland (one of the founders of Scrum) in the way that we implemented time-tracking (see his article http://scrum.jeffsutherland.com/2007/03/time-tracking-is-anti-scrum-what-do-you.html). In SonicAgile, time-tracking is disabled by default. If you want to use this feature then the project owner must enable time-tracking in Project Settings. You can choose to estimate using either days or hours. If you are estimating at the level of stories then it makes more sense to choose days. Otherwise, if you are estimating at the level of tasks then it makes more sense to use hours. After you enable time-tracking then you can assign three estimates to a story: Original Estimate – This is the estimate that you enter when you first create a story. You don’t change this estimate. Time Spent – This is the amount of time that you have already devoted to the story. You update the time spent on each story during your daily standup meeting. Time Left – This is the amount of time remaining to complete the story. Again, you update the time left during your daily standup meeting. So when you first create a story, you enter an original estimate that becomes the time left. During each daily standup meeting, you update the time spent and time left for each story on the Kanban. If you had perfect predicative power, then the original estimate would always be the same as the sum of the time spent and the time left. For example, if you predict that a story will take 5 days to complete then on day 3, the story should have 3 days spent and 2 days left. Unfortunately, never in the history of mankind has anyone accurately predicted the exact amount of time that it takes to complete a story. For this reason, SonicAgile does not update the time spent and time left automatically. Each day, during the daily standup, your team should update the time spent and time left for each story. For example, the following table shows the history of the time estimates for a story that was originally estimated to take 3 days but, eventually, takes 5 days to complete: Day Original Estimate Time Spent Time Left Day 1 3 days 0 days 3 days Day 2 3 days 1 day 2 days Day 3 3 days 2 days 2 days Day 4 3 days 3 days 2 days Day 5 3 days 4 days 0 days In the table above, everything goes as predicted until you reach day 3. On day 3, the team realizes that the work will require an additional two days. The situation does not improve on day 4. All of the sudden, on day 5, all of the remaining work gets done. Real work often follows this pattern. There are long periods when nothing gets done punctuated by occasional and unpredictable bursts of progress. We designed SonicAgile to make it as easy as possible to track the time spent and time left on a story. Detecting when a Story Goes Over the Original Estimate Sometimes, stories take much longer than originally estimated. There’s a surprise. For example, you discover that a new software component is incompatible with existing software components. Or, you discover that you have to go through a month-long certification process to finish a story. In those cases, the Product Owner has a legitimate reason to halt work on a story and re-evaluate the business value of the story. For example, the Product Owner discovers that a story will require weeks to implement instead of days, then the story might not be worth the expense. SonicAgile displays a warning on both the Backlog and the Kanban when the time spent on a story goes over the original estimate. An icon of a clock is displayed. Time-Tracking and Tasks Another optional feature of SonicAgile is tasks. If you enable Tasks in Project Settings then you can break stories into one or more tasks. You can perform time-tracking at the level of a story or at the level of a task. If you don’t break a story into tasks then you can enter the time left and time spent for the story. As soon as you break a story into tasks, then you can no longer enter the time left and time spent at the level of the story. Instead, the time left and time spent for a story is rolled up from its tasks. On the Kanban, you can see how the time left and time spent for each task gets rolled up into each story. The progress bar for the story is rolled up from the progress bars for each task. The original estimate is never rolled up – even when you break a story into tasks. A story’s original estimate is entered separately from the original estimates of each of the story’s tasks. Summary Not every Agile team can avoid time-tracking. You might be forced to track time to get paid, to detect when you are spending too much time on a particular story, or to track the amount of time that you are devoting to different types of tasks. We designed time-tracking in SonicAgile to require the least amount of work to track the information that you need. Time-tracking is an optional feature. If you enable time-tracking then you can track the original estimate, time left, and time spent for each story and task. You can use time-tracking with SonicAgile for free. Register at http://SonicAgile.com.

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  • get the current time in C

    - by Antrromet
    I want to get the current time of my system. For that i'm using the following code in C. time_t now; struct tm *mytime = localtime(&now); if ( strftime(buffer, sizeof buffer, "%X", mytime) ) { printf("time1 = \"%s\"\n", buffer); } But the problem of this code is that its giving some random time.Also the random time is different all the time.I want the current time of my system. Can anyone please tell me how to solve this issue?

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  • About floating point precision and why do we still use it

    - by system_is_b0rken
    Floating point has always been troublesome for precision on large worlds. This article explains behind-the-scenes and offers the obvious alternative - fixed point numbers. Some facts are really impressive, like: "Well 64 bits of precision gets you to the furthest distance of Pluto from the Sun (7.4 billion km) with sub-micrometer precision. " Well sub-micrometer precision is more than any fps needs (for positions and even velocities), and it would enable you to build really big worlds. My question is, why do we still use floating point if fixed point has such advantages? Most rendering APIs and physics libraries use floating point (and suffer it's disadvantages, so developers need to get around them). Are they so much slower? Additionally, how do you think scalable planetary engines like outerra or infinity handle the large scale? Do they use fixed point for positions or do they have some space dividing algorithm?

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  • C++ floating point precision

    - by Davinel
    double a = 0.3; std::cout.precision(20); std::cout << a << std::endl; result: 0.2999999999999999889 double a, b; a = 0.3; b = 0; for (char i = 1; i <= 50; i++) { b = b + a; }; std::cout.precision(20); std::cout << b << std::endl; result: 15.000000000000014211 So.. 'a' is smaller than it should be. But if we take 'a' 50 times - result will be bigger than it should be. Why is this? And how to get correct result in this case?

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  • Setting minimum number of decimal places for std::ostream precision

    - by Phil Boltt
    Hi, Is there a way to set the "minimum" number of decimal places that a std::ostream will output? For example, say I have two doubles that I want to print: double a = 0; double b = 0.123456789; I can set my maximum decimal precision so that I output b exactly std::cout << std::setprecision(9) << b << std::endl; Is there a way to set "minimum" precision so that std::cout << a << std::endl; yields "0.0", not just "0"? Thanks! Phil

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  • Loss of precision - int -> float or double

    - by stan
    I have an exam question i am revising for and the question is for 4 marks "In java we can assign a int to a double or a float". Will this ever loose infromation and why? I have put that because ints are normally of fixed length or size - the precision for sotring data is finite, where storing information in floating point can be infinite, essentially we loose infromation because of this Now i am a little sketchy as to whetehr or not i am hitting the right areas here. I very sure it will loose precision but i cant exactly put my finger on why. Can i getsome help please Thanks

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  • time(NULL) returning different time

    - by cornerback84
    I am trying to get current time in C using time_t current_time = time(NULL). As I understand, it would return me the current time of system. I am later trying to convert it into GMT time using struct tm* gmt = gmtime(&current_time). I print both times using ctime() and asctime() functions. The current time on my system is GMT + 1. But gmtime() returns me the same time as current_time is. I could not understand why gmtime() is returning me same time. Any help will be appreciated.

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  • Should Professional Development occur on company time?

    - by jshu
    As a first-time part-time software developer at a small consulting company, I'm struggling to organise time to further my own software development knowledge - whether that's reading a book, keeping up with the popular questions on StackOverflow, researching a technology we're using in-depth, or following the front page of Hacker News. I can see results borne from my self-allocated study time, but listing and demonstrating the skills and knowledge gained through Professional Development is difficult. The company does not have any defined PD policy, and there's a lot of pressure to get something deliverable done now! when working for consultants. I've checked what my coworkers do, and they don't appear to allocate any time to self-improvement; they just work at the problems they're given, looking up specific MSDN references, code samples, and the like as they need them. I realise that PD policy is going to vary across companies of different size and culture, and a company like my own is probably a bit of an edge case. I'd love to hear views and experiences from more seasoned developers; especially those who have to make the PD policy choices in their team or company. I'd also like to learn about the more radical approaches to PD, even if they're completely out there; it's always interesting to see what other people are trying. Not quite a summary, but what I'm trying to ask: Is it common or recommended for companies to allocate PD time? Whose responsibility is it to ensure a developer's knowledge and skills are up to date? Should a part-time work schedule inspire a lower ratio of PD time : work? How can a developer show non-developer coworkers that reading blogs and books is net productive? Is reading blogs and books actually net productive? (references welcomed) Is writing blogs effective as a way of PD? (a recent theme on Hacker News) This is sort of a broad question because I don't know exactly which questions I need to ask here, so any thoughts on relevant issues I haven't addressed are very welcome.

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  • How to bill a client for frequently-interrupted time

    - by Greg
    I find that when I'm working on hourly-billable projects (in particular, those that are research/design/architecture-oriented as opposed to straight coding) that I'm easily distracted by any number of things (email, grab a drink (loss of focus, but nature happens), link off the webpage I was reading, wandering mind (easy when the job calls for a lot of thinking), etc.) This results in very fragmented time, far too incremental IMO to accurately track with a timeclock, and some time very gray. I frequently end up billing for only some fraction of the elapsed time I spent in order to feel fair, but sometimes it takes a really long time to put in an 8-hour day. By contrast, when I've worked for salary I've not worried about whether I'm actively working at any given minute, I just get the job done, and I've never had anything but stellar reviews/feedback from past salaried employers, so I think I get the job done well. I personally believe in an 80/20 cycle: I get 80% of my work done during an inspired 20% of my time. But I have to screw around the other 80% of the time in order to get that first 20%. So the question: what billing/time-tracking policy can I adopt in order to be fair to my hourly customers without having to write off my own less-productive 80% that a salaried employer is willing to overlook in light of the complete package? Note: This question is not about how to be more productive or focused. It's about how to work around whatever salient limitations that I have in a way that's both fair to me and to my customers. Update: A little clarification (to pre-emptively stop some righteous indignation): I currently have a half dozen different project/client groups. It's not a great situation and I'm working at reducing it down to two, but that's my current reality. It's very easy to get off on a thread related to a different project than the one I'm clocking, and I'm not always conscious of it at the time. [I did not intend the question to mean that I was off playing games or making personal calls, etc., and have adjusted wording above to be clearer. Most of the time. I am only human, and sometimes the mind does force you to take a break! :-)]

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  • Problem measuring N times the execution time of a code block

    - by Nazgulled
    EDIT: I just found my problem after writing this long post explaining every little detail... If someone can give me a good answer on what I'm doing wrong and how can I get the execution time in seconds (using a float with 5 decimal places or so), I'll mark that as accepted. Hint: The problem was on how I interpreted the clock_getttime() man page. Hi, Let's say I have a function named myOperation that I need to measure the execution time of. To measure it, I'm using clock_gettime() as it was recommend here in one of the comments. My teacher recommends us to measure it N times so we can get an average, standard deviation and median for the final report. He also recommends us to execute myOperation M times instead of just one. If myOperation is a very fast operation, measuring it M times allow us to get a sense of the "real time" it takes; cause the clock being used might not have the required precision to measure such operation. So, execution myOperation only one time or M times really depends if the operation itself takes long enough for the clock precision we are using. I'm having trouble dealing with that M times execution. Increasing M decreases (a lot) the final average value. Which doesn't make sense to me. It's like this, on average you take 3 to 5 seconds to travel from point A to B. But then you go from A to B and back to A 5 times (which makes it 10 times, cause A to B is the same as B to A) and you measure that. Than you divide by 10, the average you get is supposed to be the same average you take traveling from point A to B, which is 3 to 5 seconds. This is what I want my code to do, but it's not working. If I keep increasing the number of times I go from A to B and back A, the average will be lower and lower each time, it makes no sense to me. Enough theory, here's my code: #include <stdio.h> #include <time.h> #define MEASUREMENTS 1 #define OPERATIONS 1 typedef struct timespec TimeClock; TimeClock diffTimeClock(TimeClock start, TimeClock end) { TimeClock aux; if((end.tv_nsec - start.tv_nsec) < 0) { aux.tv_sec = end.tv_sec - start.tv_sec - 1; aux.tv_nsec = 1E9 + end.tv_nsec - start.tv_nsec; } else { aux.tv_sec = end.tv_sec - start.tv_sec; aux.tv_nsec = end.tv_nsec - start.tv_nsec; } return aux; } int main(void) { TimeClock sTime, eTime, dTime; int i, j; for(i = 0; i < MEASUREMENTS; i++) { printf(" » MEASURE %02d\n", i+1); clock_gettime(CLOCK_REALTIME, &sTime); for(j = 0; j < OPERATIONS; j++) { myOperation(); } clock_gettime(CLOCK_REALTIME, &eTime); dTime = diffTimeClock(sTime, eTime); printf(" - NSEC (TOTAL): %ld\n", dTime.tv_nsec); printf(" - NSEC (OP): %ld\n\n", dTime.tv_nsec / OPERATIONS); } return 0; } Notes: The above diffTimeClock function is from this blog post. I replaced my real operation with myOperation() because it doesn't make any sense to post my real functions as I would have to post long blocks of code, you can easily code a myOperation() with whatever you like to compile the code if you wish. As you can see, OPERATIONS = 1 and the results are: » MEASURE 01 - NSEC (TOTAL): 27456580 - NSEC (OP): 27456580 For OPERATIONS = 100 the results are: » MEASURE 01 - NSEC (TOTAL): 218929736 - NSEC (OP): 2189297 For OPERATIONS = 1000 the results are: » MEASURE 01 - NSEC (TOTAL): 862834890 - NSEC (OP): 862834 For OPERATIONS = 10000 the results are: » MEASURE 01 - NSEC (TOTAL): 574133641 - NSEC (OP): 57413 Now, I'm not a math wiz, far from it actually, but this doesn't make any sense to me whatsoever. I've already talked about this with a friend that's on this project with me and he also can't understand the differences. I don't understand why the value is getting lower and lower when I increase OPERATIONS. The operation itself should take the same time (on average of course, not the exact same time), no matter how many times I execute it. You could tell me that that actually depends on the operation itself, the data being read and that some data could already be in the cache and bla bla, but I don't think that's the problem. In my case, myOperation is reading 5000 lines of text from an CSV file, separating the values by ; and inserting those values into a data structure. For each iteration, I'm destroying the data structure and initializing it again. Now that I think of it, I also that think that there's a problem measuring time with clock_gettime(), maybe I'm not using it right. I mean, look at the last example, where OPERATIONS = 10000. The total time it took was 574133641ns, which would be roughly 0,5s; that's impossible, it took a couple of minutes as I couldn't stand looking at the screen waiting and went to eat something.

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  • MS SQL datetime precision problem

    - by Nailuj
    I have a situation where two persons might work on the same order (stored in an MS SQL database) from two different computers. To prevent data loss in the case where one would save his copy of the order first, and then a little later the second would save his copy and overwrite the first, I've added a check against the lastSaved field (datetime) before saving. The code looks roughly like this: private bool orderIsChangedByOtherUser(Order localOrderCopy) { // Look up fresh version of the order from the DB Order databaseOrder = orderService.GetByOrderId(localOrderCopy.Id); if (databaseOrder != null && databaseOrder.LastSaved > localOrderCopy.LastSaved) { return true; } else { return false; } } This works for most of the time, but I have found one small bug. If orderIsChangedByOtherUser returns false, the local copy will have its lastSaved updated to the current time and then be persisted to the database. The value of lastSaved in the local copy and the DB should now be the same. However, if orderIsChangedByOtherUser is run again, it sometimes returns true even though no other user has made changes to the DB. When debugging in Visual Studio, databaseOrder.LastSaved and localOrderCopy.LastSaved appear to have the same value, but when looking closer they some times differ by a few milliseconds. I found this article with a short notice on the millisecond precision for datetime in SQL: Another problem is that SQL Server stores DATETIME with a precision of 3.33 milliseconds (0. 00333 seconds). The solution I could think of for this problem, is to compare the two datetimes and consider them equal if they differ by less than say 10 milliseconds. My question to you is then: are there any better/safer ways to compare two datetime values in MS SQL to see if they are exactly the same?

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  • Precision error on matrix multiplication

    - by Wam
    Hello all, Coding a matrix multiplication in my program, I get precision errors (inaccurate results for large matrices). Here's my code. The current object has data stored in a flattened array, row after row. Other matrix B has data stored in a flattened array, column after column (so I can use pointer arithmetic). protected double[,] multiply (IMatrix B) { int columns = B.columns; int rows = Rows; int size = Columns; double[,] result = new double[rows,columns]; for (int row = 0; row < rows; row++) { for (int col = 0; col < columns; col++) { unsafe { fixed (float* ptrThis = data) fixed (float* ptrB = B.Data) { float* mePtr = ptrThis + row*rows; float* bPtr = ptrB + col*columns; double value = 0.0; for (int i = 0; i < size; i++) { value += *(mePtr++) * *(bPtr++); } result[row, col] = value; } } } } } Actually, the code is a bit more complicated : I do the multiply thing for several chunks (so instead of having i from 0 to size, I go from localStart to localStop), then sum up the resulting matrices. My problem : for a big matrix I get precision error : NUnit.Framework.AssertionException: Error at (0,1) expected: <6.4209571409444209E+18> but was: <6.4207619776304906E+18> Any idea ?

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