1 files changed, 85 insertions, 0 deletions
diff --git a/StdLib/LibC/Math/e_log2.c b/StdLib/LibC/Math/e_log2.c
new file mode 100644
index 0000000000..5d15cd3b01
--- /dev/null
+++ b/StdLib/LibC/Math/e_log2.c
@@ -0,0 +1,85 @@
+
+/* @(#)e_log.c 1.3 95/01/18 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunSoft, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+#include  <LibConfig.h>
+#include  <sys/EfiCdefs.h>
+#if defined(LIBM_SCCS) && !defined(lint)
+__RCSID("$NetBSD: e_log2.c,v 1.1 2005/07/21 12:55:58 christos Exp $");
+#endif
+
+#include "math.h"
+#include "math_private.h"
+
+#if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */
+  // potential divide by 0 -- near line 53, (x-x)/zero is on purpose
+  #pragma warning ( disable : 4723 )
+#endif
+
+static const double
+ln2 = 0.6931471805599452862268,
+two54   =  1.80143985094819840000e+16,  /* 43500000 00000000 */
+Lg1 = 6.666666666666735130e-01,  /* 3FE55555 55555593 */
+Lg2 = 3.999999999940941908e-01,  /* 3FD99999 9997FA04 */
+Lg3 = 2.857142874366239149e-01,  /* 3FD24924 94229359 */
+Lg4 = 2.222219843214978396e-01,  /* 3FCC71C5 1D8E78AF */
+Lg5 = 1.818357216161805012e-01,  /* 3FC74664 96CB03DE */
+Lg6 = 1.531383769920937332e-01,  /* 3FC39A09 D078C69F */
+Lg7 = 1.479819860511658591e-01;  /* 3FC2F112 DF3E5244 */
+
+static const double zero   =  0.0;
+
+double
+__ieee754_log2(double x)
+{
+  double hfsq,f,s,z,R,w,t1,t2,dk;
+  int32_t k,hx,i,j;
+  u_int32_t lx;
+
+  EXTRACT_WORDS(hx,lx,x);
+
+  k=0;
+  if (hx < 0x00100000) {      /* x < 2**-1022  */
+      if (((hx&0x7fffffff)|lx)==0)
+    return -two54/zero;   /* log(+-0)=-inf */
+      if (hx<0) return (x-x)/zero;  /* log(-#) = NaN */
+      k -= 54; x *= two54; /* subnormal number, scale up x */
+      GET_HIGH_WORD(hx,x);
+  }
+  if (hx >= 0x7ff00000) return x+x;
+  k += (hx>>20)-1023;
+  hx &= 0x000fffff;
+  i = (hx+0x95f64)&0x100000;
+  SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */
+  k += (i>>20);
+  f = x-1.0;
+  dk = (double)k;
+  if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */
+      if (f==zero)
+        return (dk);
+      R = f*f*(0.5-0.33333333333333333*f);
+      return (dk-(R-f)/ln2);
+  }
+  s = f/(2.0+f);
+  z = s*s;
+  i = hx-0x6147a;
+  w = z*z;
+  j = 0x6b851-hx;
+  t1= w*(Lg2+w*(Lg4+w*Lg6));
+  t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
+  i |= j;
+  R = t2+t1;
+  if(i>0) {
+      hfsq=0.5*f*f;
+      return (dk-(hfsq-s*(hfsq+R)-f)/ln2);
+  } else
+    return (dk-((s*(f-R))-f)/ln2);
+}