From 7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 Mon Sep 17 00:00:00 2001 From: Eric Andersen Date: Thu, 22 Nov 2001 14:04:29 +0000 Subject: 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 --- libm/scalb.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) create mode 100644 libm/scalb.c (limited to 'libm/scalb.c') 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 . 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__ */ -- cgit v1.2.3