import newlib-2000-02-17 snapshot

1 files changed, 72 insertions, 0 deletions

diff --git a/newlib/libm/mathfp/sf_logarithm.c b/newlib/libm/mathfp/sf_logarithm.c
new file mode 100644
index 000000000..224482f13
--- /dev/null
+++ b/newlib/libm/mathfp/sf_logarithm.c
@@ -0,0 +1,72 @@
+
+/* @(#)z_logarithmf.c 1.0 98/08/13 */
+/******************************************************************
+ * The following routines are coded directly from the algorithms
+ * and coefficients given in "Software Manual for the Elementary
+ * Functions" by William J. Cody, Jr. and William Waite, Prentice
+ * Hall, 1980.
+ ******************************************************************/
+/******************************************************************
+ * Logarithm
+ *
+ * Input:
+ *   x - floating point value
+ *   ten - indicates base ten numbers
+ *
+ * Output:
+ *   logarithm of x
+ *
+ * Description:
+ *   This routine calculates logarithms.
+ *
+ *****************************************************************/
+
+#include "fdlibm.h"
+#include "zmath.h"
+
+static const float a[] = { -0.5527074855 };
+static const float b[] = { -0.6632718214e+1 };
+static const float C1 = 0.693145752;
+static const float C2 = 1.428606820e-06;
+static const float C3 = 0.4342944819;
+
+float
+_DEFUN (logarithmf, (float, int),
+        float x _AND
+        int ten)
+{
+  int N;
+  float f, w, z;
+
+  /* Check for domain error here. */
+  if (x <= 0.0)
+    {
+      errno = ERANGE;
+      return (z_notanum_f.f);
+    }
+
+  /* Get the exponent and mantissa where x = f * 2^N. */
+  f = frexpf (x, &N);
+
+  z = f - 0.5;
+
+  if (f > __SQRT_HALF)
+    z = (z - 0.5) / (f * 0.5 + 0.5);
+  else
+    {
+      N--;
+      z /= (z * 0.5 + 0.5);
+    }
+  w = z * z;
+
+  /* Use Newton's method with 4 terms. */
+  z += z * w * (a[0]) / ((w + 1.0) * w + b[0]);
+
+  if (N != 0)
+    z = (N * C2 + z) + N * C1;
+
+  if (ten)
+    z *= C3;
+
+  return (z);
+}