Part I of port of Rhombus math library

git-svn-id: http://svn.code.sf.net/p/nuttx/code/trunk@5269 42af7a65-404d-4744-a932-0658087f49c3

nuttx/lib/math/lib_log.c

@@ -0,0 +1,113 @@
+/*
+ * Copyright (C) 2009, 2010 Nick Johnson <nickbjohnson4224 at gmail.com>
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <apps/math.h>
+#include <float.h>
+
+float logf(float x) {
+	float y, y_old, ey, epsilon;
+
+	y = 0.0;
+	y_old = 1.0;
+	epsilon = FLT_EPSILON;
+
+	while (y > y_old + epsilon || y < y_old - epsilon) {
+		y_old = y;
+		ey = exp(y);
+		y -= (ey - x) / ey;
+
+		if (y > 700.0) {
+			y = 700.0;
+		}
+		if (y < -700.0) {
+			y = -700.0;
+		}
+
+		epsilon = (fabs(y) > 1.0) ? fabs(y) * FLT_EPSILON : FLT_EPSILON;
+	}
+
+	if (y == 700.0) {
+		return INFINITY;
+	}
+	if (y == -700.0) {
+		return INFINITY;
+	}
+
+	return y;
+}
+
+double log(double x) {
+	double y, y_old, ey, epsilon;
+
+	y = 0.0;
+	y_old = 1.0;
+	epsilon = DBL_EPSILON;
+
+	while (y > y_old + epsilon || y < y_old - epsilon) {
+		y_old = y;
+		ey = exp(y);
+		y -= (ey - x) / ey;
+
+		if (y > 700.0) {
+			y = 700.0;
+		}
+		if (y < -700.0) {
+			y = -700.0;
+		}
+
+		epsilon = (fabs(y) > 1.0) ? fabs(y) * DBL_EPSILON : DBL_EPSILON;
+	}
+
+	if (y == 700.0) {
+		return INFINITY;
+	}
+	if (y == -700.0) {
+		return INFINITY;
+	}
+
+	return y;
+}
+
+long double logl(long double x) {
+	long double y, y_old, ey, epsilon;
+
+	y = 0.0;
+	y_old = 1.0;
+	epsilon = 1e-6; //fixme
+
+	while (y > y_old + epsilon || y < y_old - epsilon) {
+		y_old = y;
+		ey = expl(y);
+		y -= (ey - x) / ey;
+
+		if (y > 700.0) {
+			y = 700.0;
+		}
+		if (y < -700.0) {
+			y = -700.0;
+		}
+	}
+
+	if (y == 700.0) {
+		return INFINITY;
+	}
+	if (y == -700.0) {
+		return INFINITY;
+	}
+
+	return y;
+}
+