| |
| /* @(#)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>>---scale by integer |
| INDEX |
| scalbn |
| INDEX |
| scalbnf |
| |
| ANSI_SYNOPSIS |
| #include <math.h> |
| double scalbn(double <[x]>, int <[y]>); |
| float scalbnf(float <[x]>, int <[y]>); |
| |
| TRAD_SYNOPSIS |
| #include <math.h> |
| double scalbn(<[x]>,<[y]>) |
| double <[x]>; |
| int <[y]>; |
| float scalbnf(<[x]>,<[y]>) |
| float <[x]>; |
| int <[y]>; |
| |
| DESCRIPTION |
| <<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times |
| 2 to the power <[n]>. The result is computed by manipulating the |
| exponent, rather than by actually performing an exponentiation or |
| multiplication. |
| |
| RETURNS |
| <[x]> times 2 to the power <[n]>. |
| |
| PORTABILITY |
| Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V |
| Interface Definition (Issue 2). |
| |
| */ |
| |
| /* |
| * 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 */ |
