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August 2016

How Bloomberg is Advancing C++ at Scale--John Lakos

By Adrien Hamelin | Aug 19, 2016 02:03 PM | Tags: efficiency community

Interesting interview:

How Bloomberg is Advancing C++ at Scale

by John Lakos

From the article:

John Lakos manages the Bloomberg Development Environment group, which offers a set of C++ software libraries, development tools, and methodology to well over a thousand Bloomberg developers. He is an authority on large-scale C++ software infrastructure, receiving recent acclaim for two publications by Pearson Education on methodology for industrial software development [Part 1, Part 2]. BDE and its libraries are open source and can be found on GitHub. In this conversation, Lakos discusses the importance of instilling process and discipline in all software development projects...

CppCon 2015 C++ Rcpp: Seamless R and C++ Integration--Matt P. Dziubinski

By Adrien Hamelin | Aug 19, 2016 01:52 PM | Tags: performance community

Have you registered for CppCon 2016 in September? Don’t delay – Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Rcpp: Seamless R and C++ Integration

by Matt P. Dziubinski

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

R is an open-source statistical language designed with a focus on data analysis. While its historical roots are in statistical applications, it is currently experiencing a rapid growth in popularity in all fields where data matters: from data science, through bioinformatics and finance, to machine learning. Key strengths contributing to this growth include its rich libraries ecosystem (over 6 thousands packages at the moment of writing) – often authored by the leading researchers in the field, providing early access to the latest techniques; beautiful, high-quality visualizations – supporting seamless exploratory data analysis and producing stunning presentations; all of this available in an interactive environment resulting in high productivity through fast iteration times.

At the same time, there are no free lunches in programming: the dynamic, interactive nature of R does have its costs, including a significant impact on run-time performance. In an era of growing data sizes and increasingly realistic models this concern is only becoming more important.

In this talk we provide an introduction to Rcpp – a library allowing smooth integration of R with C++, combining the productivity benefits of R for data science together with the performance of C++. First released in 2005, today it’s the most popular language extension for R -- used by over 400 packages. We'll also discuss challenges (as well as possible solutions) involved in integrating modern C++ code, and demonstrate the usage of popular C++ libraries in practice. We’ll conclude the talk with the RInside package allowing to embed R in C++.

CppCon 2015 C++ on the Web: Ponies for developers without pwn’ing users--JF Bastien

By Adrien Hamelin | Aug 17, 2016 01:51 PM | Tags: performance community

Have you registered for CppCon 2016 in September? Don’t delay – Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

C++ on the Web: Ponies for developers without pwn’ing users

by JF Bastien

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Is it possible to write apps in C++ that run in the browser with native code speed? Yes. Can you do this without the security problems associated with running native code downloaded from the net? Yes and yes. Come to this session to learn how.

We'll showcase some resource-intensive applications that have been compiled to run in the browser. These applications run as fast as native code with access to cornerstone native programming APIs—modern C++ STL, OpenGL, files and processes with full access to C++’s concurrency and parallelism—all in an architecture- and OS-agnostic packaging. Then, we'll describe how we deliver native code on the web securely, so developers get their C++ ponies and users don’t get pwn’d. We’ll also touch on the fuzzing, code randomization, and sandboxing that keep the billions of web users safe.

Quick Q: Efficiency of postincrement v.s. preincrement in C++

By Adrien Hamelin | Aug 15, 2016 12:55 PM | Tags: performance advanced

Quick A: The difference is only marginal with optimizations enabled.

Recently on SO:

Efficiency of postincrement v.s. preincrement in C++

It is true - although perhaps overly strict. Pre increment doesn't necessarily introduce a data dependency - but it can.

A trivial example for exposition:

a = b++ * 2;

Here, the increment can be executed in parallel with the multiplication. The operands of both the increment and the multiplication are immediately available and do not depend on the result of either operation.

Another example:

a = ++b * 2;

Here, the multiplication must be executed after the increment, because one of the operands of the multiplication depends on the result of the increment.

Of course, these statements do slightly different things, so the compiler might not always be able to transform the program from one form to the other while keeping the semantics the same - which is why using the post increment might make a slight difference in performance.

A practical example, using a loop:

for(int i= 0; arr[i++];)
    count++;

for(int i=-1; arr[++i];)
    count++;

One might think that the latter is necessarily faster if they reason that "post-increment makes a copy" - which would have been very true in the case of non-fundamental types. However, due to the data dependency (and because int is a fundamental type with no overload function for increment operators), the former can theoretically be more efficient. Whether it is depends on the cpu architecture, and the ability of the optimizer.

For what it's worth - in a trivial program, on x86 arch, using g++ compiler with optimization enabled, the above loops had identical assembly output, so they are perfectly equivalent in that case.

 

Rules of thumb:

If the counter is a fundamental type and the result of increment is not used, then it makes no difference whether you use post/pre increment.

If the counter is not a fundamental type and the result of the increment is not used and optimizations are disabled, then pre increment may be more efficient. With optimizations enabled, there is no difference.

If the counter is a fundamental type and the result of increment is used, then post increment can theoretically be marginally more efficient - in some cpu architecture - in some context - using some compiler.

If the counter is a complex type and the result of the increment is used, then pre increment is typically faster than post increment. Also see R Sahu's answer regarding this case.

CppCon 2015 std::allocator Is to Allocation what std::vector Is to Vexation--Andrei Alexandrescu

By Adrien Hamelin | Aug 15, 2016 12:43 PM | Tags: performance efficiency

Have you registered for CppCon 2016 in September? Don’t delay – Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

std::allocator Is to Allocation what std::vector Is to Vexation

by Andrei Alexandrescu

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

std::allocator has an inglorious past, murky present, and cheerless future. STL introduced allocators as a stop gap for the now antiquated segmented memory models of the 1990s. Their design was limited and in many ways wasn't even aiming at helping allocation that much. Because allocators were there, they simply continued being there, up to the point they became impossible to either uproot or make work, in spite of valiant effort spent by the community.

But this talk aims at spending less time on poking criticism at std::allocator and more on actually defining allocator APIs that work.

Scalable, high-performance memory allocation is a topic of increasing importance in today's demanding applications. For such, std::allocator simply doesn't work. This talk discusses the full design of a memory allocator created from first principles. It is generic, componentized, and composable for supporting application-specific allocation patterns.

Take benefit from simple laziness -- Krzysztof Ostrowski

By fj | Aug 14, 2016 11:26 PM | Tags: None

Presentation of simple techniques that can be used to delay execution of costly computations.

Take benefit from simple laziness

by Krzysztof Ostrowski

From the article:

In the C++ world lazy evaluation is usually linked to templates and their property that separates definition from actual instantiation. Given that we can, for instance, delay binding of a symbol.

Besides the above, we have old plain short circuiting inherited from C language: logical operators like && (and), || (or) and ternary operator ?:. They can be used as constructions to lazy execute (expressions must be valid C++) some of the expressions. With short circuiting we want to delay or skip execution of costly operations.

CppCon 2015 Lessons in Sustainability: How to Maintain a C++ Codebase for Decades--Titus Winters

By Adrien Hamelin | Aug 12, 2016 02:06 PM | Tags: intermediate efficiency community

Have you registered for CppCon 2016 in September? Don’t delay – Registration is open now.

While we wait for this year’s event, we’re featuring videos of some of the 100+ talks from CppCon 2015 for you to enjoy. Here is today’s feature:

Lessons in Sustainability: How to Maintain a C++ Codebase for Decades

by Titus Winters

(watch on YouTube) (watch on Channel 9)

Summary of the talk:

Google maintains (we believe) the largest monolithic C++ codebase in the world with over 100M lines of C++ code. Early commits to this repository date back to the late 1990s. About 4000 engineers submit at least one change in C++ every week. We’ve learned a few things about what it takes to maintain a codebase at this scale.

In this talk I’ll present some of the lessons we’ve learned over the years with respect to policies, technology, education, design, and maintenance of a long-lived monolithic codebase.

CppCast Episode 67: CMake Server with Stephen Kelly

By robwirving | Aug 12, 2016 07:59 AM | Tags: None

Episode 67 of CppCast the only podcast for C++ developers by C++ developers. In this episode Rob and Jason are joined by Stephen Kelley to discuss his work on the CMake Server project which will enable advanced tooling for CMake.

CppCast Episode 67: CMake Server with Stephen Kelly

by Rob Irving and Jason Turner

About the interviewee:

Stephen Kelly first encountered CMake through working on KDE and like many C++ developers, did his best to ignore the buildsystem completely. That worked well for 4 years until 2011 when the modularization of KDE libraries led to a desire to simplify and upstream as much as possible to Qt and CMake. Since then, Stephen has been responsible for many core features and designs of 'Modern CMake' and now tries to lead designs for its future.

Turning Egyptian Division Into Logarithms -- David Sanders

By insideoutclub | Aug 12, 2016 05:40 AM | Tags: None

Insights I've had while reading Elements of Programming and From Mathematics to Generic Programming

Turning Egyptian Division into Logarithms

by David Sanders

From the article:

I have benefitted greatly from multiple readings of Elements of Programming by Alexander Stepanov and Paul McJones as well as From Mathematics to Generic Programming by Stepanov and Daniel Rose. Each time I read either work, I learn something new.

In this article, I describe an extension to the ancient Egyptian division algorithm to yield logarithm and remainder in addition to quotient and remainder.