How to use constant powers of 2 readable in c++?

Question

I need several integer constants with 2^n and 2^n - 1 in my GNU c++ code.

What is a good practise to keep the code readable? The code uses decimal values at the moment 4294967296 and 65536 which is hard to debug in future.

2^12 is not implemented in standard C++ and pow(2.0,12.0) uses double.

if (buffer_length == 4294967295){ } // code example, I want to make more readable

Micha Wiedenmann · Accepted Answer · 2015-06-13T19:07:13.870

3

You can use the shift left operator:

if (buffer_length == 1 << 12){ }

edited Jun 13 '15 at 19:07

answered Jun 13 '15 at 18:20

Micha Wiedenmann

This solution is well readable. Can you imagine a better solution than `2 << 32 - 1` for `2^n-1` for the ...11111111 bit patterns? – Jonas Stein Jun 13 '15 at 18:30
4

This should be `1 << 12` (or `1U << 12`). – Mark B Jun 13 '15 at 18:46
1

@Jonas: Why not `if (buffer_length + 1 == 1u << 12)` ? – Ben Voigt Jun 13 '15 at 19:18
@BenVoigt In my eyes the code should represent the problem where it is possible. That will make it less error prone and more readable. – Jonas Stein Mar 02 '16 at 22:29

score 0 · Answer 2 · answered Jun 13 '15 at 18:23

0

Use hex. It should be pretty easy for anyone to figure out that it's a special number.

answered Jun 13 '15 at 18:23

James

@JonasStein You're mixing up hex and binary. – James Jun 13 '15 at 18:36
hex is not so easy to read with human eyes: `2^64 = 0x10000000000000000` and `2^64-1 = 0xffffffffffffffff` One has to count the number of f and 0 which is error prone and difficult to read. – Jonas Stein Jun 13 '15 at 18:37
3

@JonasStein then do what everyone else does and give the constants names and use those instead of having magic numbers all over. – James Jun 13 '15 at 18:40

2 Answers2