Add the gaussian random number generator.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/map65@2533 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

libm65/gran.c

@@ -0,0 +1,28 @@
+#include <stdlib.h>
+#include <math.h>
+
+/* Generate gaussian random float with mean=0 and std_dev=1 */
+float gran_()
+{
+  float fac,rsq,v1,v2;
+  static float gset;
+  static int iset;
+
+  if(iset){
+    /* Already got one */
+    iset = 0;
+    return gset;
+  }
+  /* Generate two evenly distributed numbers between -1 and +1
+   * that are inside the unit circle
+   */
+  do {
+    v1 = 2.0 * (float)rand() / RAND_MAX - 1;
+    v2 = 2.0 * (float)rand() / RAND_MAX - 1;
+    rsq = v1*v1 + v2*v2;
+  } while(rsq >= 1.0 || rsq == 0.0);
+  fac = sqrt(-2.0*log(rsq)/rsq);
+  gset = v1*fac;
+  iset++;
+  return v2*fac;
+}