Proper conversion of RGB to HSL

rgb_to_hsl.c

/*
  RGB to HSL

  Compile with:  gcc rgb_to_hsl.c -lm -o rgb_to_hsl
*/

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

struct hsl
{
  int   h;
  float s;
  float l;
};

struct rgb 
{ 
  uint8_t r; 
  uint8_t g; 
  uint8_t b; 
};

float max_3(float x, float y, float z)
{
  x = (x > y) ? x : y;
  x = (x > z) ? x : z;
  return x;
}

float min_3(float x, float y, float z)
{
  x = (x < y) ? x : y;
  x = (x < z) ? x : z;
  return x;
}

struct hsl rgb_to_hsl(uint8_t r, uint8_t g, uint8_t b)
{
  struct hsl output;
  float rf = r / 255.0;
  float gf = g / 255.0;
  float bf = b / 255.0;
  float max = max_3(rf, bf, gf);
  float min = min_3(rf, bf, gf);
  float h, s, l;
  h = s = l = (max + min) / 2.0;
  if(max == min)
  {
    h = s = 0.0;
  }
  else
  {
    float d = max - min;
    s = (l > 0.5) ? d / (2.0 - min - max) : d / (max + min);
    if(max == rf)
    {
      h = (gf - bf) / d;
      if(gf < bf) h += 6.0;
    }
    else if(max == gf) h = (bf - rf) / d + 2.0;
    else if(max == bf) h = (r - g) / d + 4.0;
    h = h / 6.0;
  }
  output.h = roundf(360 * h);
  output.s = s;
  output.l = l;
  return output;
}

int main(void) 
{
  struct rgb input  = {230, 67, 34};
  struct hsl output = rgb_to_hsl(input.r, input.g, input.b);
  printf("\nConverted rgb(%d, %d, %d) to rgb(%d°, %.2f%%, %.2f%%)\n\n", 
    input.r, input.g, input.b, 
    output.h, output.s * 100, output.l * 100);
  return 0;
}