Why is Rust slightly slower than C?

Post by imtringued » Thu, Sep 12, 2019, 12:57 PM UTC

dbaupp wrote: post #160

steveklabnik wrote: post #92

Earlier quoted context omitted.

Bounds checking is a “zero cost abstraction” in the sense that it is both “pay for what you use” and “you couldn’t implement it yourself any better.” That said, the implemention is not as fast as it theoretically can be, because the compiler isn’t always removing bounds checks that are provably true. When const generic lands, you will be able to make those assertions! A basic implementation is in nightly.

This is taking zero-cost abstraction to the extreme, and I think waters down the concept to the point that it almost isn't useful. One can argue that any feature is a zero-cost abstraction for the exact set of trade-offs it has (in the limit: "you couldn't implement a feature that executes this exact sequence of instructions 'mov ...' any better if you did it by hand"). I think focusing on a hypothetical perfect code…

Post by ncmncm » Thu, Sep 12, 2019, 1:06 PM UTC

fnord123 wrote: post #196

ncmncm wrote: post #195

Earlier quoted context omitted.

You do all those things with C++ (or, for fpga, asic, etc., without). There is exactly zero benefit to dropping to C first. And, nobody suggested anybody actually laughs at C developers. We just don't see them.

> You do all those things with C++ (or, for fpga, asic, etc., without). There is exactly zero benefit to dropping to C first. That's my point. The performance tuning is generally not between C++ or C hence why you cannot extrapolate your experiences to the rest of the finance industry. >And, nobody suggested anybody actually laughs at C developers. You said, "In the finance world, you would be laughed out of the room…

Post by ncmncm » Thu, Sep 12, 2019, 1:50 PM UTC

fluffything wrote: post #183

unrealhoang wrote: post #180

Earlier quoted context omitted.

You can write zero ops destructor as well. So yes, RAII is zero-cost abstraction.

I literally said so.

Post by fulafel » Thu, Sep 12, 2019, 1:55 PM UTC

jeremyjh wrote: post #79

codesushi42 wrote: post #76

Earlier quoted context omitted.

It is routine for C++ programs to be substantially faster than a C program that attempts the same job, even though C++ suffers from the same aliasing flaws C has. In the finance world, you would be laughed out of the room for proposing C for a performance-critical task. That depends on how you write your C++ programs. Virtual functions, runtime type information, STL, RAII ownership can all be performance hits in C++…

Is there really a performance cost from RAII? Presumably whatever a destructor has to do to release resources, C code would also have to do.

Post by monocasa » Thu, Sep 12, 2019, 2:23 PM UTC

graycat wrote: post #159

monocasa wrote: post #82

Earlier quoted context omitted.

The compiler (off the top of my head this applies to GCC, clang, and MSVC, dont know about ICC) generally understands the C string functions at a fundamental level and will emit optimized code instead of a function call that will use hardware instructions and might know the size of the buffer at compile time. For instance on GCC you have to specify -fno-builtin to say "you don't know what you think you know about c l…

I get it now: My view of HN just went down to the sewer: We're into the old, bitter, go out back and fight it out, religious computer language wars. And there C is one of the grand sacred subjects: C is the greatest. The greatest, best ever. The greatest, fastest of all time, never to be improved on. Pure genius. Pure gold. And C programmers are like people who climb Mount Everest barefoot with no tools and the only…