1 files changed, 84 insertions, 0 deletions
diff --git a/shared/common/clc.c b/shared/common/clc.c
new file mode 100644
index 0000000..b4d1208
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+++ b/shared/common/clc.c
@@ -0,0 +1,84 @@
+/* Copyright (c) 2004 krzYszcz and others.
+ * For information on usage and redistribution, and for a DISCLAIMER OF ALL
+ * WARRANTIES, see the file, "LICENSE.txt," in this distribution.  */
+
+#include <math.h>
+
+/* Problem:  find a function f : p -> q (where p is user's curve control
+   parameter, q is log factor) such that the curves will bend in
+   a semi-linear way over the p's range of 0..1.  The curve function is
+   then g(x, p) = (exp(f(p) * x) - 1) / (exp(f(p)) - 1), where x is
+   curve's domain.  If, for example, the points g(0.5, p) are to make
+   a semi-linear pattern, then the solution is a function f that minimizes
+   the integral of the error function e(p) = sqr(((1-p)/2)-g(.5, p))
+   over 0..1.  Until someone does this analytically, we are left with
+   a lame formula, which has been tweaked and tested in gnuplot:
+   f(p) = h(p) / (1 - h(p)), where h(p) = (((p + 1e-20) * 1.2) ** .41) * .91.
+   The file curve.gp, in the sickle's source directory, may come handy,
+   in case there is anyone, who fancy tweaking it even further.
+
+   To implement this, start from these equations:
+     nhops = npoints - 1
+     bb * mm ^ nhops = bb + 1
+     (bb ^ 2) * (mm ^ nhops) = ((exp(ff/2) - 1) / (exp(ff) - 1)) ^ 2
+
+   and calculate:
+     hh = pow(((p + c1) * c2), c3) * c4
+     ff = hh / (1 - hh)
+     eff = exp(ff) - 1
+     gh = (exp(ff * .5) - 1) / eff
+     bb = gh * (gh / (1 - (gh + gh)))
+     mm = ((exp(ff * (1/nhops)) - 1) / (eff * bb)) + 1
+
+   The loop is:
+     for (vv = bb, i = 0; i <= nhops; vv *= mm, i++)
+         result = (vv - bb) * (y1 - y0) + y0
+   where y0, y1 are start and destination values
+
+   This formula generates curves with < .000004% deviation from the straight
+   line for p = 0 at half-domain, range 1.  There are no nans for -1 <= p <= 1.
+*/
+
+#define CLCCURVE_C1   1e-20
+#define CLCCURVE_C2   1.2
+#define CLCCURVE_C3   0.41
+#define CLCCURVE_C4   0.91
+
+void clccurve_coefs(int nhops, double crv, double *bbp, double *mmp)
+{
+    if (nhops > 0)
+    {
+	double hh, ff, eff, gh;
+	if (crv < 0)
+	{
+	    if (crv < -1.)
+		crv = -1.;
+	    hh = pow(((CLCCURVE_C1 - crv) * CLCCURVE_C2), CLCCURVE_C3)
+		* CLCCURVE_C4;
+	    ff = hh / (1. - hh);
+	    eff = exp(ff) - 1.;
+	    gh = (exp(ff * .5) - 1.) / eff;
+	    *bbp = gh * (gh / (1. - (gh + gh)));
+	    *mmp = 1. / (((exp(ff * (1. / (double)nhops)) - 1.) /
+			  (eff * *bbp)) + 1.);
+	    *bbp += 1.;
+	}
+	else
+	{
+	    if (crv > 1.)
+		crv = 1.;
+	    hh = pow(((crv + CLCCURVE_C1) * CLCCURVE_C2), CLCCURVE_C3)
+		* CLCCURVE_C4;
+	    ff = hh / (1. - hh);
+	    eff = exp(ff) - 1.;
+	    gh = (exp(ff * .5) - 1.) / eff;
+	    *bbp = gh * (gh / (1. - (gh + gh)));
+	    *mmp = ((exp(ff * (1. / (double)nhops)) - 1.) /
+		    (eff * *bbp)) + 1.;
+	}
+    }
+    else if (crv < 0)
+	*bbp = 2., *mmp = 1.;
+    else
+	*bbp = *mmp = 1.;
+}