gamma_curve method from dcraw

dcraw.gamma_curve.c

void CLASS gamma_curve (double pwr, double ts, int mode, int imax)
{
  int i;
  double g[6], bnd[2]={0,0}, r;

  g[0] = pwr;
  g[1] = ts;
  g[2] = g[3] = g[4] = 0;
  bnd[g[1] >= 1] = 1;
  if (g[1] && (g[1]-1)*(g[0]-1) <= 0) {
    for (i=0; i < 48; i++) {
      g[2] = (bnd[0] + bnd[1])/2;
      if (g[0]) bnd[(pow(g[2]/g[1],-g[0]) - 1)/g[0] - 1/g[2] > -1] = g[2];
      else	bnd[g[2]/exp(1-1/g[2]) < g[1]] = g[2];
    }
    g[3] = g[2] / g[1];
    if (g[0]) g[4] = g[2] * (1/g[0] - 1);
  }
  if (g[0]) g[5] = 1 / (g[1]*SQR(g[3])/2 - g[4]*(1 - g[3]) +
		(1 - pow(g[3],1+g[0]))*(1 + g[4])/(1 + g[0])) - 1;
  else      g[5] = 1 / (g[1]*SQR(g[3])/2 + 1
		- g[2] - g[3] -	g[2]*g[3]*(log(g[3]) - 1)) - 1;
  if (!mode--) {
    memcpy (gamm, g, sizeof gamm);
    return;
  }
  for (i=0; i < 0x10000; i++) {
    curve[i] = 0xffff;
    if ((r = (double) i / imax) < 1)
      curve[i] = 0x10000 * ( mode
	? (r < g[3] ? r*g[1] : (g[0] ? pow( r,g[0])*(1+g[4])-g[4]    : log(r)*g[2]+1))
	: (r < g[2] ? r/g[1] : (g[0] ? pow((r+g[4])/(1+g[4]),1/g[0]) : exp((r-1)/g[2]))));
  }
}