nano optimization - Page 59

Is there table with timing(cost) of C functions?

- by DSblizzard

Preferable for x86-32 gcc implementation

some pointer to understanding GCC source code

hi, I'm student working on optimizing GCC for multi-core processor. I tried going through the source code, it is difficult to follow through it since I need to add some code to the back end. Can anyone suggest some good resource which explains the code flow through the different phases. Also suggest some development environment for debugging GCC mainly to step through the code. Is it possible on windows?

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How can i get rid of 'ORA-01489: result of string concatenation is too long' in this query?

- by core_pro

this query gets the dominating sets in a network. so for example given a network A<----->B B<----->C B<----->D C<----->E D<----->C D<----->E F<----->E it returns B,E B,F A,E but it doesn't work for large data because i'm using string methods in my result. i have been trying to remove the string methods and return a view or something but to no avail With t as (select 'A' as per1, 'B' as per2 from dual union all select 'B','C' from dual union all select 'B','D' from dual union all select 'C','B' from dual union all select 'C','E' from dual union all select 'D','C' from dual union all select 'D','E' from dual union all select 'E','C' from dual union all select 'E','D' from dual union all select 'F','E' from dual) ,t2 as (select distinct least(per1, per2) as per1, greatest(per1, per2) as per2 from t union select distinct greatest(per1, per2) as per1, least(per1, per2) as per1 from t) ,t3 as (select per1, per2, row_number() over (partition by per1 order by per2) as rn from t2) ,people as (select per, row_number() over (order by per) rn from (select distinct per1 as per from t union select distinct per2 from t) ) ,comb as (select sys_connect_by_path(per,',')||',' as p from people connect by rn > prior rn ) ,find as (select p, per2, count(*) over (partition by p) as cnt from ( select distinct comb.p, t3.per2 from comb, t3 where instr(comb.p, ','||t3.per1||',') > 0 or instr(comb.p, ','||t3.per2||',') > 0 ) ) ,rnk as (select p, rank() over (order by length(p)) as rnk from find where cnt = (select count(*) from people) order by rnk ) select distinct trim(',' from p) as p from rnk where rnk.rnk = 1`

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Is opening too many datacontexts bad?

- by ryudice

I've been checking my application with linq 2 sql profiler, and I noticed that it opens a lot of datacontexts, most of them are opened by the linq datasource I used, since my repositories use only the instance stored in Request.Items, is it bad to open too many datacontext? and how can I make my linqdatasource to use the datacontext that I store in Request.Items for the duration of the request? thanks for any help!

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Postgre database ignoring created index ?!

- by drasto

I have an Postgre database and a table called my_table. There are 4 columns in that table (id, column1, column2, column3). The id column is primary key, there are no other constrains or indexes on columns. The table has about 200000 rows. I want to print out all rows which has value of column column2 equal(case insensitive) to 'value12'. I use this: SELECT * FROM my_table WHERE column2 = lower('value12') here is the execution plan for this statement(result of set enable_seqscan=on; EXPLAIN SELECT * FROM my_table WHERE column2 = lower('value12')): Seq Scan on my_table (cost=0.00..4676.00 rows=10000 width=55) Filter: ((column2)::text = 'value12'::text) I consider this to be to slow so I create an index on column column2 for better prerformance of searches: CREATE INDEX my_index ON my_table (lower(column2)) Now I ran the same select: SELECT * FROM my_table WHERE column2 = lower('value12') and I expect it to be much faster because it can use index. However it is not faster, it is as slow as before. So I check the execution plan and it is the same as before(see above). So it still uses sequential scen and it ignores the index! Where is the problem ?

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SQL Server indexed view matching of views with joins not working

- by usr

Does anyone have experience of when SQL Servr 2008 R2 is able to automatically match indexed view (also known as materialized views) that contain joins to a query? for example the view select dbo.Orders.Date, dbo.OrderDetails.ProductID from dbo.OrderDetails join dbo.Orders on dbo.OrderDetails.OrderID = dbo.Orders.ID cannot be automatically matched to the same exact query. When I select directly from this view ith (noexpand) I actually get a much faster query plan that does a scan on the clustered index of the indexed view. Can I get SQL Server to do this matching automatically? I have quite a few queries and views... I am on enterprise edition of SQL Server 2008 R2.

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How can I optimize retrieving lowest edit distance from a large table in SQL?

- by Matt

Hey, I'm having troubles optimizing this Levenshtein Distance calculation I'm doing. I need to do the following: Get the record with the minimum distance for the source string as well as a trimmed version of the source string Pick the record with the minimum distance If the min distances are equal (original vs trimmed), choose the trimmed one with the lowest distance If there are still multiple records that fall under the above two categories, pick the one with the highest frequency Here's my working version: DECLARE @Results TABLE ( ID int, [Name] nvarchar(200), Distance int, Frequency int, Trimmed bit ) INSERT INTO @Results SELECT ID, [Name], (dbo.Levenshtein(@Source, [Name])) As Distance, Frequency, 'False' As Trimmed FROM MyTable INSERT INTO @Results SELECT ID, [Name], (dbo.Levenshtein(@SourceTrimmed, [Name])) As Distance, Frequency, 'True' As Trimmed FROM MyTable SET @ResultID = (SELECT TOP 1 ID FROM @Results ORDER BY Distance, Trimmed, Frequency) SET @Result = (SELECT TOP 1 [Name] FROM @Results ORDER BY Distance, Trimmed, Frequency) SET @ResultDist = (SELECT TOP 1 Distance FROM @Results ORDER BY Distance, Trimmed, Frequency) SET @ResultTrimmed = (SELECT TOP 1 Trimmed FROM @Results ORDER BY Distance, Trimmed, Frequency) I believe what I need to do here is to.. Not dumb the results to a temporary table Do only 1 select from `MyTable` Setting the results right in the select from the initial select statement. (Since select will set variables and you can set multiple variables in one select statement) I know there has to be a good implementation to this but I can't figure it out... this is as far as I got: SELECT top 1 @ResultID = ID, @Result = [Name], (dbo.Levenshtein(@Source, [Name])) As distOrig, (dbo.Levenshtein(@SourceTrimmed, [Name])) As distTrimmed, Frequency FROM MyTable WHERE /* ... yeah I'm lost */ ORDER BY distOrig, distTrimmed, Frequency Any ideas?

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Better way to summarize data about stop times?

- by Vimvq1987

This question is close to this: http://stackoverflow.com/questions/2947963/find-the-period-of-over-speed Here's my table: Longtitude Latitude Velocity Time 102 401 40 2010-06-01 10:22:34.000 103 403 50 2010-06-01 10:40:00.000 104 405 0 2010-06-01 11:00:03.000 104 405 0 2010-06-01 11:10:05.000 105 406 35 2010-06-01 11:15:30.000 106 403 60 2010-06-01 11:20:00.000 108 404 70 2010-06-01 11:30:05.000 109 405 0 2010-06-01 11:35:00.000 109 405 0 2010-06-01 11:40:00.000 105 407 40 2010-06-01 11:50:00.000 104 406 30 2010-06-01 12:00:00.000 101 409 50 2010-06-01 12:05:30.000 104 405 0 2010-06-01 11:05:30.000 I want to summarize times when vehicle had stopped (velocity = 0), include: it had stopped since "when" to "when" in how much minutes, how many times it stopped and how much time it stopped. I wrote this query to do it: select longtitude, latitude, MIN(time), MAX(time), DATEDIFF(minute, MIN(Time), MAX(time)) as Timespan from table_1 where velocity = 0 group by longtitude,latitude select DATEDIFF(minute, MIN(Time), MAX(time)) as minute into #temp3 from table_1 where velocity = 0 group by longtitude,latitude select COUNT(*) as [number]from #temp select SUM(minute) as [totaltime] from #temp3 drop table #temp This query return: longtitude latitude (No column name) (No column name) Timespan 104 405 2010-06-01 11:00:03.000 2010-06-01 11:10:05.000 10 109 405 2010-06-01 11:35:00.000 2010-06-01 11:40:00.000 5 number 2 totaltime 15 You can see, it works fine, but I really don't like the #temp table. Is there anyway to query this without use a temp table? Thank you.

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How can I strip Python logging calls without commenting them out?

- by cdleary

Today I was thinking about a Python project I wrote about a year back where I used logging pretty extensively. I remember having to comment out a lot of logging calls in inner-loop-like scenarios (the 90% code) because of the overhead (hotshot indicated it was one of my biggest bottlenecks). I wonder now if there's some canonical way to programmatically strip out logging calls in Python applications without commenting and uncommenting all the time. I'd think you could use inspection/recompilation or bytecode manipulation to do something like this and target only the code objects that are causing bottlenecks. This way, you could add a manipulator as a post-compilation step and use a centralized configuration file, like so: [Leave ERROR and above] my_module.SomeClass.method_with_lots_of_warn_calls [Leave WARN and above] my_module.SomeOtherClass.method_with_lots_of_info_calls [Leave INFO and above] my_module.SomeWeirdClass.method_with_lots_of_debug_calls Of course, you'd want to use it sparingly and probably with per-function granularity -- only for code objects that have shown logging to be a bottleneck. Anybody know of anything like this? Note: There are a few things that make this more difficult to do in a performant manner because of dynamic typing and late binding. For example, any calls to a method named debug may have to be wrapped with an if not isinstance(log, Logger). In any case, I'm assuming all of the minor details can be overcome, either by a gentleman's agreement or some run-time checking. :-)

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Does replacing statements by expressions using the C++ comma operator could allow more compiler opti

- by Gabriel Cuvillier

The C++ comma operator is used to chain individual expressions, yielding the value of the last executed expression as the result. For example the skeleton code (6 statements, 6 expressions): step1; step2; if (condition) step3; return step4; else return step5; May be rewritten to: (1 statement, 6 expressions) return step1, step2, condition? step3, step4 : step5; I noticed that it is not possible to perform step-by-step debugging of such code, as the expression chain seems to be executed as a whole. Does it means that the compiler is able to perform special optimizations which are not possible with the traditional statement approach (specially if the steps are const or inline)? Note: I'm not talking about the coding style merit of that way of expressing sequence of expressions! Just about the possible optimisations allowed by replacing statements by expressions.

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How to improve performance of map that loads new overlay images

- by anthonysomerset

I have inherited a website to maintain that uses a html map overlaying a real map to link specific countries to specific pages. previously it loaded the default map image, then with some javascript it would change the image src to an image with that particular country in a different colour on mouseover and reset the image source back to the original image on mouse out to make maintenance (adding new countries) easier i made the initial map a background image by utilising some CSS for the div tag, and then created new images for each country which only had that countries hightlight so that the images remain fairly small. this works great but theres one issue which is particularly noticeable on slower internet connections when you hover over a country if you dont have the image file in your browser cache or downloaded it wont load the image unless you hover over another country and then back onto the first country - i guess this is due to the image having to manually be downloaded on first hover. My question: is it possible to force the load of these extra images AFTER the page and all the other assets have finished loading so that this behaviour is all but eliminated? the html code for the MAP is as follows: <div class="gtmap"><img id="Image-Maps_6200909211657061" src="<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png" usemap="#Image-Maps_6200909211657061" alt="We offer Guided Motorcycle Tours all around the world" width="615" height="296" /> <map id="_Image-Maps_6200909211657061" name="Image-Maps_6200909211657061"> <area shape="poly" coords="511,134,532,107,542,113,520,141" href="/guided-motorcycle-tours-japan/" alt="Guided Japan Motorcycle Tours" title="Japan" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-japan.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="252,61,266,58,275,64,262,68" href="/guided-motorcycle-tour.php?iceland-motorcycle-adventure-39" alt="Guided Iceland Motorcycle Tours" title="Iceland" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-iceland.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="587,246,597,256,577,279,568,270" href="/guided-motorcycle-tour.php?new-zealand-south-island-adventure-10" alt="New Zealand Guided Motorcycle Tours" title="New Zealand" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-nz.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="418,133,412,145,412,154,421,178,430,180,430,166,443,154,443,145,438,144,433,142,430,138,431,130,430,129,425,128" href="/guided-motorcycle-tours-india/" alt="India Guided Motorcycle Tours" title="India" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-india.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="460,152,466,149,474,165,470,171,466,161" href="/guided-motorcycle-tours-laos/" alt="Laos Guided Motorcycle Tours" title="Laos" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-laos.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="468,179,475,166,468,152,475,152,482,169" href="/guided-motorcycle-tour.php?indochina-motorcycle-adventure-tour-32" onClick="javascript: pageTracker._trackPageview('/internal-links/guided-tours/map/vietnam');" alt="Vietnam Guided Motorcycle Tours" title="Vietnam" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-viet.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="330,239,337,235,347,226,352,233,351,243,344,250,335,253,327,255,323,249,322,242,323,241" href="/guided-motorcycle-tours-southafrica/" alt="South Africa Guided Motorcycle Tours" title="South Africa" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-sa.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="290,77,293,86,298,96,286,102,285,97,285,89,282,84,282,79" href="/guided-motorcycle-tour.php?great-britain-isle-of-man-scotland-wales-uk-18" alt="United Kingdom" title="United Kingdom Guided Motorcycle Tours" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-uk.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="357,118,368,118,369,126,345,129,338,125,338,117,342,115,348,116" href="/guided-motorcycle-tour.php?explore-turkey-adventure-45" alt="Turkey" title="Turkey Guided Motorcycle Tours" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-turkey.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="206,95,193,101,185,101,178,106,165,111,157,109,147,105,134,103,121,103,107,103,96,103,86,104,81,99,77,91,70,83,62,79,60,72,61,64,59,57,60,51,71,50,83,49,95,50,107,54,117,53,129,47,137,36,148,37,163,38,177,44,187,54,195,60,184,72,191,80,200,87" href="/guided-motorcycle-tours-canada/" alt="Guided Canada Motorcycle Tours" title="Canada" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-canada.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="61,75,60,62,60,55,59,44,51,44,43,43,36,42,28,43,23,48,17,51,15,62,19,74,27,79,19,83,16,93,35,83,43,77,50,75,55,75" href="/guided-motorcycle-tours-alaska/" alt="Guided Alaska Motorcycle Tours" title="Alaska" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-alaska.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="82,101,99,101,133,101,148,105,161,110,172,106,187,100,180,113,171,122,165,131,159,149,147,141,137,140,129,147,120,141,112,138,103,137,93,132,86,122,86,112,86,106" href="/guided-motorcycle-tours-usa/" alt="USA Guided Motorcycle Tours" title="USA" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-usa.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="178,225,180,214,175,208,174,204,178,198,174,193,167,192,157,199,158,204,164,211,167,218" href="/guided-motorcycle-tour.php?peru-machu-picchu-adventure-25" alt="Peru Guided Motorcycle Tours" title="Peru" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-peru.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="172,226,169,239,166,256,166,267,164,279,171,277,174,262,175,250,179,234,180,225,176,224" href="/guided-motorcycle-tours-chile/" alt="Guided Chile Motorcycle Tours" title="Chile" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-chile.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> <area shape="poly" coords="199,260,194,261,187,265,184,276,183,296,170,292,168,282,174,270,174,257,177,245,180,230,190,228,205,237,199,245" href="/guided-motorcycle-tours-argentina/" alt="Guided Argentina Motorcycle Tours" title="Argentina" onmouseover="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-arg.png';" onmouseout="if(document.images) document.getElementById('Image-Maps_6200909211657061').src='<?php echo cdnhttpsCheck(); ?>assets/wmap/a-guided-tours-map-blank.png';" /> </map> </div> The <?php echo cdnhttpsCheck(); ?> is just a site specific function that gets the correct web domain/url from a config file to load resources from CDN where possible (eg all non HTTPS requests) We are loading Jquery at the bottom of the HTML if anybody wonders why it is missing from the code snippet for reference, the page with the map in question is found here: http://www.motoquest.com/guided-motorcycle-tours/

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Wrappers of primitive types in arraylist vs arrays

- by ismail marmoush

Hi, In "Core java 1" I've read CAUTION: An ArrayList is far less efficient than an int[] array because each value is separately wrapped inside an object. You would only want to use this construct for small collections when programmer convenience is more important than efficiency. But in my software I've already used Arraylist instead of normal arrays due to some requirements, though "The software is supposed to have high performance and after I've read the quoted text I started to panic!" one thing I can change is changing double variables to Double so as to prevent auto boxing and I don't know if that is worth it or not, in next sample algorithm public void multiply(final double val) { final int rows = getSize1(); final int cols = getSize2(); for (int i = 0; i < rows; i++) { for (int j = 0; j < cols; j++) { this.get(i).set(j, this.get(i).get(j) * val); } } } My question is does changing double to Double makes a difference ? or that's a micro optimizing that won't affect anything ? keep in mind I might be using large matrices.2nd Should I consider redesigning the whole program again ?

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Find point which sum of distances to set of other points is minimal

- by Pawel Markowski

I have one set (X) of points (not very big let's say 1-20 points) and the second (Y), much larger set of points. I need to choose some point from Y which sum of distances to all points from X is minimal. I came up with an idea that I would treat X as a vertices of a polygon and find centroid of this polygon, and then I will choose a point from Y nearest to the centroid. But I'm not sure whether centroid minimizes sum of its distances to the vertices of polygon, so I'm not sure whether this is a good way? Is there any algorithm for solving this problem? Points are defined by geographical coordinates.

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Trying to reduce the speed overhead of an almost-but-not-quite-int number class

- by Fumiyo Eda

I have implemented a C++ class which behaves very similarly to the standard int type. The difference is that it has an additional concept of "epsilon" which represents some tiny value that is much less than 1, but greater than 0. One way to think of it is as a very wide fixed point number with 32 MSBs (the integer parts), 32 LSBs (the epsilon parts) and a huge sea of zeros in between. The following class works, but introduces a ~2x speed penalty in the overall program. (The program includes code that has nothing to do with this class, so the actual speed penalty of this class is probably much greater than 2x.) I can't paste the code that is using this class, but I can say the following: +, -, +=, <, > and >= are the only heavily used operators. Use of setEpsilon() and getInt() is extremely rare. * is also rare, and does not even need to consider the epsilon values at all. Here is the class: #include <limits> struct int32Uepsilon { typedef int32Uepsilon Self; int32Uepsilon () { _value = 0; _eps = 0; } int32Uepsilon (const int &i) { _value = i; _eps = 0; } void setEpsilon() { _eps = 1; } Self operator+(const Self &rhs) const { Self result = *this; result._value += rhs._value; result._eps += rhs._eps; return result; } Self operator-(const Self &rhs) const { Self result = *this; result._value -= rhs._value; result._eps -= rhs._eps; return result; } Self operator-( ) const { Self result = *this; result._value = -result._value; result._eps = -result._eps; return result; } Self operator*(const Self &rhs) const { return this->getInt() * rhs.getInt(); } // XXX: discards epsilon bool operator<(const Self &rhs) const { return (_value < rhs._value) || (_value == rhs._value && _eps < rhs._eps); } bool operator>(const Self &rhs) const { return (_value > rhs._value) || (_value == rhs._value && _eps > rhs._eps); } bool operator>=(const Self &rhs) const { return (_value >= rhs._value) || (_value == rhs._value && _eps >= rhs._eps); } Self &operator+=(const Self &rhs) { this->_value += rhs._value; this->_eps += rhs._eps; return *this; } Self &operator-=(const Self &rhs) { this->_value -= rhs._value; this->_eps -= rhs._eps; return *this; } int getInt() const { return(_value); } private: int _value; int _eps; }; namespace std { template<> struct numeric_limits<int32Uepsilon> { static const bool is_signed = true; static int max() { return 2147483647; } } }; The code above works, but it is quite slow. Does anyone have any ideas on how to improve performance? There are a few hints/details I can give that might be helpful: 32 bits are definitely insufficient to hold both _value and _eps. In practice, up to 24 ~ 28 bits of _value are used and up to 20 bits of _eps are used. I could not measure a significant performance difference between using int32_t and int64_t, so memory overhead itself is probably not the problem here. Saturating addition/subtraction on _eps would be cool, but isn't really necessary. Note that the signs of _value and _eps are not necessarily the same! This broke my first attempt at speeding this class up. Inline assembly is no problem, so long as it works with GCC on a Core i7 system running Linux!

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Is ToString() optimized by compiler?

- by TheVillageIdiot

Suppose I've following Code: Console.WriteLine("Value1: " + SomeEnum.Value1.ToString() + "\r\nValue2: " + SomeOtherEnum.Value2.ToString()); Will Compiler Optimize this to: Console.WriteLine("Value1: " + SomeEnum.Value1 + "\r\nValue2: " + SomeOtherEnum.Value2); I've checked it with IL Disassembler and there are calls to IL_005a: callvirt instance string [mscorlib]System.Object::ToString() I don't know if JIT optimizes this.

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Coalesce function for PHP?

- by mikl

Many programming languages has a coalesce function (example). PHP, sadly, does not. What would be the most efficient way to implement one in PHP?

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Quickest way to write to file in java

- by user1097772

I'm writing an application which compares directory structure. First I wrote an application which writes gets info about files - one line about each file or directory. My soulution is: calling method toFile Static PrintWriter pw = new PrintWriter(new BufferedWriter( new FileWriter("DirStructure.dlis")), true); String line; // info about file or directory public void toFile(String line) { pw.println(line); } and of course pw.close(), at the end. My question is, can I do it quicker? What is the quickest way? Edit: quickest way = quickest writing in the file

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Fastest way to convert string to integer in PHP

- by nickf

Using PHP, what's the fastest way to convert a string like this: "123" to an integer? Why is that particular method the fastest? What happens if it gets unexpected input, such as "hello" or an array?

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Can I use Duff's Device on an array in C?

- by Ben Fossen

I have a loop here and I want to make it run faster. I am passing in a large array. I recently heard of Duff's Device can it be applied to this for loop? any ideas? for (i = 0; i < dim; i++) { for (j = 0; j < dim; j++) { dst[RIDX(dim-1-j, i, dim)] = src[RIDX(i, j, dim)]; } }

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how to speed up the code??

- by kaushik

in my program i have a method which requires about 4 files to be open each time it is called,as i require to take some data.all this data from the file i have been storing in list for manupalation. I approximatily need to call this method about 10,000 times.which is making my program very slow? any method for handling this files in a better ways and is storing the whole data in list time consuming what is better alternatives for list? I can give some code,but my previous question was closed as that only confused everyone as it is a part of big program and need to be explained completely to understand,so i am not giving any code,please suggest ways thinking this as a general question... thanks in advance

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Meassure website

- by s0mmer

Hi, I was wondering if it is possible to install or use any online service to measure your website's performance? I've seen many just checking the download speed of images, external files etc. But is it possible to meassure how long asp/php code takes to execute? I have a site running a bit slowly, and it would be very nice with some app/service guiding where to optimize.

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Difference between Logarithmic and Uniform cost criteria

- by Marthin

I'v got some problem to understand the difference between Logarithmic(Lcc) and Uniform(Ucc) cost criteria and also how to use it in calculations. Could someone please explain the difference between the two and perhaps show how to calculate the complexity for a problem like A+B*C (Yes this is part of an assignment =) ) Thx for any help! /Marthin

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Optimize a MySQL count each duplicate Query

- by Onema

I have the following query That gets the city name, city id, the region name, and a count of duplicate names for that record: SELECT Country_CA.City AS currentCity, Country_CA.CityID, globe_region.region_name, ( SELECT count(Country_CA.City) FROM Country_CA WHERE City LIKE currentCity ) as counter FROM Country_CA LEFT JOIN globe_region ON globe_region.region_id = Country_CA.RegionID AND globe_region.country_code = Country_CA.CountryCode ORDER BY City This example is for Canada, and the cities will be displayed on a dropdown list. There are a few towns in Canada, and in other countries, that have the same names. Therefore I want to know if there is more than one town with the same name region name will be appended to the town name. Region names are found in the globe_region table. Country_CA and globe_region look similar to this (I have changed a few things for visualization purposes) CREATE TABLE IF NOT EXISTS `Country_CA` ( `City` varchar(75) NOT NULL DEFAULT '', `RegionID` varchar(10) NOT NULL DEFAULT '', `CountryCode` varchar(10) NOT NULL DEFAULT '', `CityID` int(11) NOT NULL DEFAULT '0', PRIMARY KEY (`City`,`RegionID`), KEY `CityID` (`CityID`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; AND CREATE TABLE IF NOT EXISTS `globe_region` ( `country_code` char(2) COLLATE utf8_unicode_ci NOT NULL, `region_code` char(2) COLLATE utf8_unicode_ci NOT NULL, `region_name` varchar(50) COLLATE utf8_unicode_ci NOT NULL, PRIMARY KEY (`country_code`,`region_code`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci; The query on the top does exactly what I want it to do, but It takes way too long to generate a list for 5000 records. I would like to know if there is a way to optimize the sub-query in order to obtain the same results faster. the results should look like this City CityID region_name counter sheraton 2349269 British Columbia 1 sherbrooke 2349270 Quebec 2 sherbrooke 2349271 Nova Scotia 2 shere 2349273 British Columbia 1 sherridon 2349274 Manitoba 1

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How can I optimize this subqueried and Joined MySQL Query?

- by kevzettler

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Faster way to split a string and count characters using R?

- by chrisamiller

I'm looking for a faster way to calculate GC content for DNA strings read in from a FASTA file. This boils down to taking a string and counting the number of times that the letter 'G' or 'C' appears. I also want to specify the range of characters to consider. I have a working function that is fairly slow, and it's causing a bottleneck in my code. It looks like this: ## ## count the number of GCs in the characters between start and stop ## gcCount <- function(line, st, sp){ chars = strsplit(as.character(line),"")[[1]] numGC = 0 for(j in st:sp){ ##nested ifs faster than an OR (|) construction if(chars[[j]] == "g"){ numGC <- numGC + 1 }else if(chars[[j]] == "G"){ numGC <- numGC + 1 }else if(chars[[j]] == "c"){ numGC <- numGC + 1 }else if(chars[[j]] == "C"){ numGC <- numGC + 1 } } return(numGC) } Running Rprof gives me the following output: > a = "GCCCAAAATTTTCCGGatttaagcagacataaattcgagg" > Rprof(filename="Rprof.out") > for(i in 1:500000){gcCount(a,1,40)}; > Rprof(NULL) > summaryRprof(filename="Rprof.out") self.time self.pct total.time total.pct "gcCount" 77.36 76.8 100.74 100.0 "==" 18.30 18.2 18.30 18.2 "strsplit" 3.58 3.6 3.64 3.6 "+" 1.14 1.1 1.14 1.1 ":" 0.30 0.3 0.30 0.3 "as.logical" 0.04 0.0 0.04 0.0 "as.character" 0.02 0.0 0.02 0.0 $by.total total.time total.pct self.time self.pct "gcCount" 100.74 100.0 77.36 76.8 "==" 18.30 18.2 18.30 18.2 "strsplit" 3.64 3.6 3.58 3.6 "+" 1.14 1.1 1.14 1.1 ":" 0.30 0.3 0.30 0.3 "as.logical" 0.04 0.0 0.04 0.0 "as.character" 0.02 0.0 0.02 0.0 $sampling.time [1] 100.74 Any advice for making this code faster?

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