author | William Roberts <williamr@symbian.org> |
Fri, 23 Jul 2010 11:57:06 +0100 | |
branch | GCC_SURGE |
changeset 46 | 0a3770c1cffe |
parent 0 | e4d67989cc36 |
permissions | -rw-r--r-- |
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/* S_SCALBN.C |
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* |
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* Portions Copyright (c) 1993-1999 Nokia Corporation and/or its subsidiary(-ies). |
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* All rights reserved. |
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*/ |
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/* @(#)s_scalbn.c 5.1 93/09/24 */ |
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/* |
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* ==================================================== |
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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* |
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* Developed at SunPro, a Sun Microsystems, Inc. business. |
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* Permission to use, copy, modify, and distribute this |
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* software is freely granted, provided that this notice |
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* is preserved. |
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* ==================================================== |
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*/ |
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|
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/* |
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FUNCTION |
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<<scalbn>>, <<scalbnf>>---scale by integer |
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INDEX |
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scalbn |
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INDEX |
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scalbnf |
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|
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ANSI_SYNOPSIS |
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#include <math.h> |
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double scalbn(double <[x]>, int <[y]>); |
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float scalbnf(float <[x]>, int <[y]>); |
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|
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TRAD_SYNOPSIS |
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#include <math.h> |
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double scalbn(<[x]>,<[y]>) |
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double <[x]>; |
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int <[y]>; |
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float scalbnf(<[x]>,<[y]>) |
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float <[x]>; |
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int <[y]>; |
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|
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DESCRIPTION |
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<<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times |
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2 to the power <[n]>. The result is computed by manipulating the |
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exponent, rather than by actually performing an exponentiation or |
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multiplication. |
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|
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RETURNS |
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<[x]> times 2 to the power <[n]>. |
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PORTABILITY |
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Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V |
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Interface Definition (Issue 2). |
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54 |
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*/ |
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/* |
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* scalbn (double x, int n) |
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* scalbn(x,n) returns x* 2**n computed by exponent |
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* manipulation rather than by actually performing an |
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* exponentiation or a multiplication. |
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*/ |
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#include "FDLIBM.H" |
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static const double |
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two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
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twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
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huge = 1.0e+300, |
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tiny = 1.0e-300; |
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|
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/** |
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Scales x by n, returning x times |
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2 to the power n. The result is computed by manipulating the |
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exponent, rather than by actually performing an exponentiation or |
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multiplication. |
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@return x times 2 to the power n. |
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@param x floating point value |
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@param n integer power |
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*/ |
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EXPORT_C double scalbn (double x, int n) __SOFTFP |
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{ |
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__int32_t k,hx,lx; |
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EXTRACT_WORDS(hx,lx,x); |
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k = (hx&0x7ff00000)>>20; /* extract exponent */ |
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if (k==0) { /* 0 or subnormal x */ |
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if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
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x *= two54; |
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GET_HIGH_WORD(hx,x); |
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k = ((hx&0x7ff00000)>>20) - 54; |
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if (n< -50000) return tiny*x; /*underflow*/ |
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} |
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if (k==0x7ff) return x+x; /* NaN or Inf */ |
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k = k+n; |
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if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ |
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if (k > 0) /* normal result */ |
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{SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} |
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if (k <= -54) { |
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if (n > 50000) /* in case integer overflow in n+k */ |
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return huge*copysign(huge,x); /*overflow*/ |
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else return tiny*copysign(tiny,x); /*underflow*/ |
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} |
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k += 54; /* subnormal result */ |
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Revision: 201002
Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com>
parents:
diff
changeset
|
104 |
SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); |
e4d67989cc36
Revision: 201002
Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com>
parents:
diff
changeset
|
105 |
return x*twom54; |
e4d67989cc36
Revision: 201002
Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com>
parents:
diff
changeset
|
106 |
} |