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Groups > comp.lang.c++ > #121241
| From | Student Project <student@invalid.invalid> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: constexpr is really very smart! |
| Date | 2024-12-18 04:45 +0000 |
| Organization | To protect and to server |
| Message-ID | <vjtkcb$39cft$1@paganini.bofh.team> (permalink) |
| References | <vjndub$2glcu$1@paganini.bofh.team> <87h6726oyo.fsf@nosuchdomain.example.com> |
On 17/12/2024 20:20, Keith Thompson wrote:
> Student Project <student@invalid.invalid> writes:
>> The constexpr is really very smart because it can speed up algorithms
>> 1000 times according to Dave, Microsoft retired engineer. He has proved it
>> by creating this video:
>>
>> <https://youtu.be/8-VZoXn8f9U?si=iy1UimoWcaLG31Xi>
>>
>> On my computer it took 270 microseconds to calculate fib(35) like in his
>> example. It was almost instant at the blink of the eyes.
>
> Can you post the relevant code?
>
> [...]
>
Code in the boxed area below: (The purpose is to demonstrate constexpr NOT the recursive algorithm. The video is very clear about this).
It is the same code as in the video. G++ gives you the best result after
changing one line to:
/*constexpr*/ int result_c = fibonacci_c(num);
G++ result is (multiple runs) - All timings in milliseconds:
D:\CmdLine\C_Cpp\Chrono05>program
Fibonacci_c 9227465
Time taken: 9
Fibonacci 9227465
Time taken: 289
D:\CmdLine\C_Cpp\Chrono05>program
Fibonacci_c 9227465
Time taken: 4
Fibonacci 9227465
Time taken: 276
D:\CmdLine\C_Cpp\Chrono05>program
Fibonacci_c 9227465
Time taken: 8
Fibonacci 9227465
Time taken: 284
D:\CmdLine\C_Cpp\Chrono05>program
Fibonacci_c 9227465
Time taken: 5
Fibonacci 9227465
Time taken: 276
clang++ and Visual studio are the slowest. I don't know why.
<+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++>
#include <iostream>
#include <chrono>
int fibonacci(int n)
{
if (n <= 1)
return n;
return fibonacci(n - 2) + fibonacci(n - 1);
}
constexpr int fibonacci_c(int n)
{
if (n <= 1)
return n;
return fibonacci_c(n - 2) + fibonacci_c(n - 1);
}
int main(void)
{
// using namespace std::literals::chrono_literals;
auto start = std::chrono::high_resolution_clock::now();
constexpr int num = 35;
/*constexpr*/ int result_c = fibonacci_c(num);
std::cout << "Fibonacci_c " << result_c << "\n";
std::cout << "Time taken: " <<
std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::high_resolution_clock::now()
- start).count() << "\n";
start = std::chrono::high_resolution_clock::now();
int result = fibonacci(num);
std::cout << "Fibonacci " << result << "\n";
std::cout << "Time taken: " <<
std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::high_resolution_clock::now()
- start).count() << "\n";
}
<+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-15 20:20 +0000
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-16 11:28 +0200
Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-16 11:18 +0100
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-16 13:23 +0200
Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-16 13:43 +0100
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-17 11:08 +0200
Re: constexpr is really very smart! David Brown <david.brown@hesbynett.no> - 2024-12-17 11:10 +0100
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 03:26 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 14:39 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 07:42 -0800
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-17 12:54 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 01:33 +0200
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 13:51 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-19 00:40 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-20 02:17 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-20 14:59 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 00:07 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 10:25 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-23 17:47 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-24 05:21 -0800
Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Michael S <already5chosen@yahoo.com> - 2024-12-25 11:05 +0200
Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Michael S <already5chosen@yahoo.com> - 2024-12-25 13:33 +0200
Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-26 18:54 -0800
Re: Bignum multiplication in Python vs GMP (was: constexpr is really very smart!) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-26 18:42 -0800
Re: constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-19 19:14 +0000
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-18 09:45 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 22:00 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-19 00:57 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-19 23:45 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-20 14:31 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 00:14 +0200
Re: constexpr is really very smart! James Kuyper <jameskuyper@alumni.caltech.edu> - 2024-12-21 17:55 -0500
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-22 02:22 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 10:33 -0800
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-23 00:05 +0200
Re: constexpr is really very smart! Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-12-22 17:17 -0800
Re: constexpr is really very smart! Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-17 12:20 -0800
Re: constexpr is really very smart! Student Project <student@invalid.invalid> - 2024-12-18 04:45 +0000
Re: constexpr is really very smart! Michael S <already5chosen@yahoo.com> - 2024-12-18 14:17 +0200
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