Move powerpc specific optimizations (courtesy of apple) to powerpc

subdir.  Put together a theoretical framework for adding arch specific
optimizations.  Havn't tried this yet but it looks correct...
 -Erik

1 files changed, 103 insertions, 0 deletions

diff --git a/libm/powerpc/logb.c b/libm/powerpc/logb.c
new file mode 100644
index 000000000..3a410ba5c
--- /dev/null
+++ b/libm/powerpc/logb.c
@@ -0,0 +1,103 @@
+/*******************************************************************************
+*                                                                              *
+*      File logb.c,                                                            *
+*      Functions logb.                                                         *
+*      Implementation of logb for the PowerPC.                                 *
+*                                                                              *
+*      Copyright © 1991 Apple Computer, Inc.  All rights reserved.             *
+*                                                                              *
+*      Written by Ali Sazegari, started on June 1991,                          *
+*                                                                              *
+*      August   26 1991: removed CFront Version 1.1d17 warnings.               *
+*      August   27 1991: no errors reported by the test suite.                 *
+*      November 11 1991: changed CLASSEXTENDED to the macro CLASSIFY and       *
+*                        + or - infinity to constants.                         *
+*      November 18 1991: changed the macro CLASSIFY to CLASSEXTENDEDint to     *
+*                        improve performance.                                  *
+*      February 07 1992: changed bit operations to macros (  object size is    *
+*                        unchanged  ).                                         *
+*      September24 1992: took the "#include support.h" out.                    *
+*      December 03 1992: first rs/6000 port.                                   *
+*      August   30 1992: set the divide by zero for the zero argument case.    *
+*      October  05 1993: corrected the environment.                            *
+*      October  17 1994: replaced all environmental functions with __setflm.   *
+*      May      28 1997: made speed improvements.                              *
+*      April    30 2001: forst mac os x port using gcc.                        *
+*                                                                              *
+********************************************************************************
+*     The C math library offers a similar function called "frexp".  It is      *
+*     different in details from logb, but similar in spirit.  This current     *
+*     implementation of logb follows the recommendation in IEEE Standard 854   *
+*     which is different in its handling of denormalized numbers from the IEEE *
+*     Standard 754.                                                            *
+*******************************************************************************/
+
+typedef union           
+      { 
+      struct {
+#if defined(__BIG_ENDIAN__)
+        unsigned long int hi;
+        unsigned long int lo;
+#else
+        unsigned long int lo;
+        unsigned long int hi;
+#endif
+      } words;
+      double dbl;
+      } DblInHex;
+
+static const double twoTo52 = 4.50359962737049600e15;              // 0x1p52
+static const double klTod = 4503601774854144.0;                    // 0x1.000008p52
+static const unsigned long int signMask = 0x80000000ul;
+static const DblInHex minusInf  = {{ 0xFFF00000, 0x00000000 }};
+
+
+/*******************************************************************************
+********************************************************************************
+*                                    L  O  G  B                                *
+********************************************************************************
+*******************************************************************************/
+
+double logb (  double x  )
+      {
+      DblInHex xInHex;
+      long int shiftedExp;
+      
+      xInHex.dbl = x;
+      shiftedExp = ( xInHex.words.hi & 0x7ff00000UL ) >> 20;
+      
+      if ( shiftedExp == 2047 ) 
+            {                                            // NaN or INF
+            if ( ( ( xInHex.words.hi & signMask ) == 0 ) || ( x != x ) )
+                  return x;                              // NaN or +INF return x
+            else
+                  return -x;                             // -INF returns +INF
+            }
+      
+      if ( shiftedExp != 0 )                             // normal number
+            shiftedExp -= 1023;                          // unbias exponent
+      
+      else if ( x == 0.0 ) 
+            {                                            // zero
+            xInHex.words.hi = 0x0UL;                      // return -infinity
+            return (  minusInf.dbl  );
+            }
+      
+      else 
+            {                                            // subnormal number
+            xInHex.dbl *= twoTo52;                       // scale up
+            shiftedExp = ( xInHex.words.hi & 0x7ff00000UL ) >> 20;
+            shiftedExp -= 1075;                          // unbias exponent
+            }
+      
+      if ( shiftedExp == 0 )                             // zero result
+            return ( 0.0 );
+      
+      else 
+            {                                            // nonzero result
+            xInHex.dbl = klTod;
+            xInHex.words.lo += shiftedExp;
+            return ( xInHex.dbl - klTod );
+            }
+      }
+