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How to write log base(2) in C/C++

stackoverflow.com › questions › 3064926 › how-to-write-log-base2-in-c-c

Simple math:

log2 (x) = logy (x) / logy (2)

where y can be anything, which for standard log functions is either 10 or e.

Answer from Adam Crume on Stack Overflow

reddit.com › r/canon › c-log 3 vs c-log 2

r/canon on Reddit: C-log 3 vs C-log 2

February 4, 2023 -

Hi I’m new to the whole high end camera thing. When I first got into shooting videos all the YouTubers were talking about C-log 3 when reviewing canon cameras. I recently for the first time heard about C-log 2. Is the difference that noticeable? What would be the differences?

Top answer

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According to Canon, C-Log 2 gives more dynamic range in shadows, but is slightly noisier as a result. C-Log 3 preserves less shadow detail but has a cleaner noise floor, meaning it's less likely noise reduction is needed in post. The reality is very few Canon cameras carry C-Log 2, and C-Log 3 in theory provides more than enough dynamic range for most canon camera's, apart from those with dual gain output (C70). That being said, C-Log 2 does preserve more information in the shadows, and does permit better shadow recovery!

2 of 3

R cameras only have Clog3 or Clog1. Dynamic range goes; Clog1 lowest, Clog 3, Clog2 highest. The r5 does not max out the dynamic range of Clog3. I assume it is similar story for the rest of the R line. So Clog2 would have only negative impact if it was used. R5 is not a great sensor, 10.3 clean stops with 8k raw in the R5. 11.9 in H2s. 12.3 in C70 Even beat by the tiny sensor in the GH6 at 11 https://www.cined.com/canon-eos-r5-lab-test-to-film-in-raw-or-not/ https://www.cined.com/fujifilm-x-h2s-lab-test-rolling-shutter-dynamic-range-and-exposure-latitude/ https://www.cined.com/canon-eos-c70-lab-test-with-the-raw-update-rolling-shutter-dynamic-range-and-latitude/ https://www.cined.com/panasonic-lumix-gh6-lab-test-rolling-shutter-dynamic-range-and-latitude/

W3Schools

w3schools.com › c › ref_math_log2.php

C Math log2() Function

The log2() function returns the base 2 logarithm of a number. The log2() function is defined in the <math.h> header file. One of the following: log2(double number); ❮ Math Functions · C Functions Tutorial · C Math Functions Tutorial · ★ ...

Videos

youtube.com

When to use Clog2 vs Clog3 | C70 Comparison

youtube.com

Le C-LOG2 sur le CANON EOS R5 Mark II et étalonnage ...

34:05

YouTube

C-Log Color Grading - Easy Techniques (Including FREE) - Premiere ...

August 16, 2024

08:27

YouTube

How to expose Canon C70 Clog 2 - YouTube

February 21, 2023

04:35

YouTube

EXPOSER LE C-LOG2 ET C-LOG3 FACILEMENT ( très facilement ) - YouTube

September 29, 2022

08:26

YouTube

YES! You CAN capture CLog2 on the CANON R5 - YouTube

Simple math:

log2 (x) = logy (x) / logy (2)

where y can be anything, which for standard log functions is either 10 or e.

2 of 15

C99 has log2 (as well as log2f and log2l for float and long double).

Cppreference

en.cppreference.com › w › c › numeric › math › log2

log2, log2f, log2l - cppreference.com

February 15, 2022 - #include <stdio.h> #include <math.h> #include <float.h> #include <errno.h> #include <fenv.h> // #pragma STDC FENV_ACCESS ON int main(void) { printf("log2(65536) = %f\n", log2(65536)); printf("log2(0.125) = %f\n", log2(0.125)); printf("log2(0x020f) = %f (highest set bit is in position 9)\n", log2(0x020f)); printf("base-5 logarithm of 125 = %f\n", log2(125)/log2(5)); // special values printf("log2(1) = %f\n", log2(1)); printf("log2(+Inf) = %f\n", log2(INFINITY)); //error handling errno = 0; feclearexcept(FE_ALL_EXCEPT); printf("log2(0) = %f\n", log2(0)); if(errno == ERANGE) perror(" errno == ERANGE"); if(fetestexcept(FE_DIVBYZERO)) puts(" FE_DIVBYZERO raised"); }

Canon Community

community.usa.canon.com › t5 › Professional-Video › ICYMI-Canon-dropped-the-C-Log-2-3-to-Canon-709-LUT › td-p › 563580

ICYMI: Canon dropped the C-Log 2/3 to Canon 709 LU... - Canon Community

January 13, 2026 - ICYMI: Canon dropped the C-Log 2/3 to Canon 709 LU...

Cplusplus

cplusplus.com › reference › cmath › log2

Cplusplus

Returns the binary (base-2) logarithm of x. Header <tgmath.h> provides a type-generic macro version of this function. Additional overloads are provided in this header (<cmath>) for the integral types: These overloads effectively cast x to a double before calculations (defined for T being any ...

Educative

educative.io › answers › what-is-log2-in-c

What is log2 in C?

Find elsewhere

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Canon Asia

snapshot.canon-asia.com › article › eng › videography-faq-what-is-canon-log

Videography FAQ: What is Canon Log? - SNAPSHOT

September 15, 2023 - There are three different Canon Log modes: the original Canon Log, Canon Log 2, and Canon Log 3.

Danielhaggett

danielhaggett.com › home › blog › canon c300 mkii log log2 or log3 which is best?

Canon C300 mkii Log Log2 or Log3 which is best?

If you are looking solely for high dynamic range, then LOG2 is the curve for you. For high contrast bright outdoor scenes the LOG 2 curve works really well. I always shoot the LOG2 Cine Gamut preset if using this LOG, as the Cine Gamut gives the greatest colour spectrum for grading.

Canon Europe

canon-europe.com › professional photography & video › stories

Enhance your filmmaking with Canon Log - Canon Europe

Technology has rapidly developed since then, with today's cutting-edge 12-bit DGO and BSI sensors delivering up to 16-stops of dynamic range. Being able to capture this extra 4-stops of latitude led to the introduction of Canon Log 2 and Canon Log 3, with the original Canon Log no longer being required in current models.

Stack Overflow

stackoverflow.com › questions › 758001 › log2-not-found-in-my-math-h

c - log2 not found in my math.h? - Stack Overflow

Top answer

1 of 5

From here:

Prototype: double log2(double anumber);
Header File: math.h (C) or cmath (C++)

Alternatively emulate it like here

#include <math.h>  
...  
// Calculates log2 of number.  
double Log2( double n )  
{  
    // log(n)/log(2) is log2.  
    return log( n ) / log( 2 );  
}

Unfortunately Microsoft does not provide it.

2 of 5

log2() is only defined in the C99 standard, not the C90 standard. Microsoft Visual C++ is not fully C99 compliant (heck, there isn't a single fully C99 compliant compiler in existence, I believe -- not even GCC fully supports it), so it's not required to provide log2().

Microsoft Learn

learn.microsoft.com › en-us › cpp › c-runtime-library › reference › log2-log2f-log2l

log2, log2f, log2l | Microsoft Learn

July 9, 2025 - double log2( double x ); float log2( float x ); //C++ only long double log2( long double x ); //C++ only float log2f( float x ); long double log2l( long double x ); #define log2(X) // Requires C11 or later ...

GeeksforGeeks

geeksforgeeks.org › c language › log2-log2f-log2l-functions-in-c

log2, log2f, log2l Functions in C - GeeksforGeeks

April 12, 2022 - log2, log2f, and log2l are functions in C that compute the logarithmic of base 2 of a given number.

Pozo Production

pozoproduction.com › blog › unleashing-the-power-of-c-log-2-on-the-canon-r5-mark-ii

Unleashing the Power of C-Log 2 on the Canon R5 Mark II — Pozo Production

January 1, 2025 - C-Log 2 is designed to unlock the full potential of your Canon R5 Mark II by maximizing dynamic range and offering a smoother, more natural image quality.

Stack Overflow

stackoverflow.com › questions › 40900069 › logarithm-base-2-in-c-language

Logarithm base 2 in C language - Stack Overflow

Top answer

1 of 2

#include <stdio.h>
#include <math.h>

int main() {
    double x = 42.0;

    printf( "log( %f ) = %f\n", x, log2(x) );

    return 0;
}

OUTPUT

% ./a.out
log( 42.000000 ) = 5.392317
%

2 of 2

You can also create a helper function which converts to any log base you wish:

Something like this:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double 
my_log(double x, int base) { 
    return log(x) / log(base); 
} 

int 
main(void) {
    double x = 42.0;

    printf("log(%f) = %f\n", x, my_log(x, 2));

    return 0;
}

Compiled with:

gcc -Wall -o logprog logprog.c -lm

Output:

log(42.000000) = 5.392317

KooR

koor.fr › C › cmath › log2.wp

KooR.fr - Fonctions log2, log2f et log2l - Langage C

Ces trois fonctions permettent de calculer le logarithme, en base 2, de la valeur passée en paramètre.

GeeksforGeeks

geeksforgeeks.org › c++ › log2-function-in-c-with-examples

log2() function in C++ with Examples - GeeksforGeeks

July 12, 2025 - // C++ program to illustrate log2() function #include <bits/stdc++.h> using namespace std; // Driver Code int main() { long b = 16; float c = 2.5; double d = 10.35; long double e = 25.5; // Logarithmic value of long datatype cout << log2(b) << "\n"; // Logarithmic value of float datatype cout << log2(c) << "\n"; // Logarithmic value of double datatype cout << log2(d) << "\n"; // Logarithmic value of long double datatype cout << log2(e) << "\n"; return 0; }

4K Shooters

4kshooters.net › home › blog › canon log 2 vs canon log 3 – which one to pick

Canon Log 2 vs Canon Log 3 – Which One to Pick | 4K Shooters

April 2, 2024 - Using ACES to go to a 709 profile. There, unfortunately, isn’t a perfect input transform for the C500, but Carlos goes with the closest option which is the C700’s Canon Log 2 IDT. Unfortunately, the colors are a little off since it isn’t tuned exactly for this camera.