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[/] [openrisc/] [trunk/] [gnu-stable/] [newlib-1.18.0/] [newlib/] [libm/] [common/] [s_scalbn.c] - Rev 859
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/* @(#)s_scalbn.c 5.1 93/09/24 */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* FUNCTION <<scalbn>>, <<scalbnf>>, <<scalbln>>, <<scalblnf>>--scale by power of FLT_RADIX (=2) INDEX scalbn INDEX scalbnf INDEX scalbln INDEX scalblnf ANSI_SYNOPSIS #include <math.h> double scalbn(double <[x]>, int <[n]>); float scalbnf(float <[x]>, int <[n]>); double scalbln(double <[x]>, long int <[n]>); float scalblnf(float <[x]>, long int <[n]>); DESCRIPTION The <<scalbn>> and <<scalbln>> functions compute @ifnottex <[x]> times FLT_RADIX to the power <[n]>. @end ifnottex @tex $x \cdot FLT\_RADIX^n$. @end tex efficiently. The result is computed by manipulating the exponent, rather than by actually performing an exponentiation or multiplication. In this floating-point implementation FLT_RADIX=2, which makes the <<scalbn>> functions equivalent to the <<ldexp>> functions. RETURNS <[x]> times 2 to the power <[n]>. A range error may occur. PORTABILITY ANSI C, POSIX SEEALSO <<ldexp>> */ /* * scalbn (double x, int n) * scalbn(x,n) returns x* 2**n computed by exponent * manipulation rather than by actually performing an * exponentiation or a multiplication. */ #include "fdlibm.h" #ifndef _DOUBLE_IS_32BITS #ifdef __STDC__ static const double #else static double #endif two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ huge = 1.0e+300, tiny = 1.0e-300; #ifdef __STDC__ double scalbn (double x, int n) #else double scalbn (x,n) double x; int n; #endif { __int32_t k,hx,lx; EXTRACT_WORDS(hx,lx,x); k = (hx&0x7ff00000)>>20; /* extract exponent */ if (k==0) { /* 0 or subnormal x */ if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ x *= two54; GET_HIGH_WORD(hx,x); k = ((hx&0x7ff00000)>>20) - 54; if (n< -50000) return tiny*x; /*underflow*/ } if (k==0x7ff) return x+x; /* NaN or Inf */ k = k+n; if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ if (k > 0) /* normal result */ {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} if (k <= -54) { if (n > 50000) /* in case integer overflow in n+k */ return huge*copysign(huge,x); /*overflow*/ else return tiny*copysign(tiny,x); /*underflow*/ } k += 54; /* subnormal result */ SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x*twom54; } #endif /* _DOUBLE_IS_32BITS */
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