Standard Libraries for EDK II.

[mirror_edk2.git] / StdLib / LibC / Math / e_log10.c

diff --git a/StdLib/LibC/Math/e_log10.c b/StdLib/LibC/Math/e_log10.c
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+/** @file\r
+  Compute the base 10 logrithm of x.\r
+\r
+  Copyright (c) 2010 - 2011, Intel Corporation. All rights reserved.<BR>\r
+  This program and the accompanying materials are licensed and made available under\r
+  the terms and conditions of the BSD License that accompanies this distribution.\r
+  The full text of the license may be found at\r
+  http://opensource.org/licenses/bsd-license.\r
+\r
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,\r
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.\r
+\r
+ * ====================================================\r
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.\r
+ *\r
+ * Developed at SunPro, a Sun Microsystems, Inc. business.\r
+ * Permission to use, copy, modify, and distribute this\r
+ * software is freely granted, provided that this notice\r
+ * is preserved.\r
+ * ====================================================\r
+\r
+  e_log10.c 5.1 93/09/24\r
+  NetBSD: e_log10.c,v 1.12 2002/05/26 22:01:51 wiz Exp\r
+**/\r
+#include  <LibConfig.h>\r
+#include  <sys/EfiCdefs.h>\r
+\r
+/* __ieee754_log10(x)\r
+ * Return the base 10 logarithm of x\r
+ *\r
+ * Method :\r
+ *  Let log10_2hi = leading 40 bits of log10(2) and\r
+ *      log10_2lo = log10(2) - log10_2hi,\r
+ *      ivln10   = 1/log(10) rounded.\r
+ *  Then\r
+ *    n = ilogb(x),\r
+ *    if(n<0)  n = n+1;\r
+ *    x = scalbn(x,-n);\r
+ *    log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))\r
+ *\r
+ * Note 1:\r
+ *  To guarantee log10(10**n)=n, where 10**n is normal, the rounding\r
+ *  mode must set to Round-to-Nearest.\r
+ * Note 2:\r
+ *  [1/log(10)] rounded to 53 bits has error  .198   ulps;\r
+ *  log10 is monotonic at all binary break points.\r
+ *\r
+ * Special cases:\r
+ *  log10(x) is NaN with signal if x < 0;\r
+ *  log10(+INF) is +INF with no signal; log10(0) is -INF with signal;\r
+ *  log10(NaN) is that NaN with no signal;\r
+ *  log10(10**N) = N  for N=0,1,...,22.\r
+ *\r
+ * Constants:\r
+ * The hexadecimal values are the intended ones for the following constants.\r
+ * The decimal values may be used, provided that the compiler will convert\r
+ * from decimal to binary accurately enough to produce the hexadecimal values\r
+ * shown.\r
+ */\r
+\r
+#include "math.h"\r
+#include "math_private.h"\r
+#include  <errno.h>\r
+\r
+#if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */\r
+  // potential divide by 0 -- near line 80, (x-x)/zero is on purpose\r
+  #pragma warning ( disable : 4723 )\r
+#endif\r
+\r
+static const double\r
+two54      =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */\r
+ivln10     =  4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */\r
+log10_2hi  =  3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */\r
+log10_2lo  =  3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */\r
+\r
+static const double zero   =  0.0;\r
+\r
+double\r
+__ieee754_log10(double x)\r
+{\r
+  double y,z;\r
+  int32_t i,k,hx;\r
+  u_int32_t lx;\r
+\r
+  EXTRACT_WORDS(hx,lx,x);\r
+\r
+  k=0;\r
+  if (hx < 0x00100000) {            /* x < 2**-1022  */\r
+    if (((hx&0x7fffffff)|lx)==0)\r
+      return -two54/zero;           /* log(+-0)=-inf */\r
+    if (hx<0) {\r
+      errno = EDOM;\r
+      return (x-x)/zero;            /* log(-#) = NaN */\r
+    }\r
+    k -= 54; x *= two54;            /* subnormal number, scale up x */\r
+    GET_HIGH_WORD(hx,x);\r
+  }\r
+  if (hx >= 0x7ff00000) return x+x;\r
+  k += (hx>>20)-1023;\r
+  i  = ((u_int32_t)k&0x80000000)>>31;\r
+  hx = (hx&0x000fffff)|((0x3ff-i)<<20);\r
+  y  = (double)(k+i);\r
+  SET_HIGH_WORD(x,hx);\r
+  z  = y*log10_2lo + ivln10*__ieee754_log(x);\r
+  return  z+y*log10_2hi;\r
+}\r