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authorEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
committerEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
commit7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 (patch)
tree3a7e8476e868ae15f4da1b7ce26b2db6f434468c /libm/scalb.c
parentc117dd5fb183afb1a4790a6f6110d88704be6bf8 (diff)
Totally rework the math library, this time based on the MacOs X
math library (which is itself based on the math lib from FreeBSD). -Erik
Diffstat (limited to 'libm/scalb.c')
-rw-r--r--libm/scalb.c87
1 files changed, 87 insertions, 0 deletions
diff --git a/libm/scalb.c b/libm/scalb.c
new file mode 100644
index 000000000..03d2de9dc
--- /dev/null
+++ b/libm/scalb.c
@@ -0,0 +1,87 @@
+#if defined(__ppc__)
+/***********************************************************************
+** File: scalb.c
+**
+** Contains: C source code for implementations of floating-point
+** scalb functions defined in header <fp.h>. In
+** particular, this file contains implementations of
+** functions scalb and scalbl for double and long double
+** formats on PowerPC platforms.
+**
+** Written by: Jon Okada, SANEitation Engineer, ext. 4-4838
+**
+** Copyright: © 1992 by Apple Computer, Inc., all rights reserved
+**
+** Change History ( most recent first ):
+**
+** 28 May 97 ali made an speed improvement for large n,
+** removed scalbl.
+** 12 Dec 92 JPO First created.
+**
+***********************************************************************/
+
+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 twoTo1023 = 8.988465674311579539e307; // 0x1p1023
+static const double twoToM1022 = 2.225073858507201383e-308; // 0x1p-1022
+
+
+/***********************************************************************
+ double scalb( double x, long int n ) returns its argument x scaled
+ by the factor 2^m. NaNs, signed zeros, and infinities are propagated
+ by this function regardless of the value of n.
+
+ Exceptions: OVERFLOW/INEXACT or UNDERFLOW inexact may occur;
+ INVALID for signaling NaN inputs ( quiet NaN returned ).
+
+ Calls: none.
+***********************************************************************/
+
+double scalb ( double x, int n )
+ {
+ DblInHex xInHex;
+
+ xInHex.words.lo = 0UL; // init. low half of xInHex
+
+ if ( n > 1023 )
+ { // large positive scaling
+ if ( n > 2097 ) // huge scaling
+ return ( ( x * twoTo1023 ) * twoTo1023 ) * twoTo1023;
+ while ( n > 1023 )
+ { // scale reduction loop
+ x *= twoTo1023; // scale x by 2^1023
+ n -= 1023; // reduce n by 1023
+ }
+ }
+
+ else if ( n < -1022 )
+ { // large negative scaling
+ if ( n < -2098 ) // huge negative scaling
+ return ( ( x * twoToM1022 ) * twoToM1022 ) * twoToM1022;
+ while ( n < -1022 )
+ { // scale reduction loop
+ x *= twoToM1022; // scale x by 2^( -1022 )
+ n += 1022; // incr n by 1022
+ }
+ }
+
+/*******************************************************************************
+* -1022 <= n <= 1023; convert n to double scale factor. *
+*******************************************************************************/
+
+ xInHex.words.hi = ( ( unsigned long ) ( n + 1023 ) ) << 20;
+ return ( x * xInHex.dbl );
+ }
+#endif /* __ppc__ */