s_scalbn.c revision 117912
12116Sjkh/* @(#)s_scalbn.c 5.1 93/09/24 */ 22116Sjkh/* 32116Sjkh * ==================================================== 42116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 52116Sjkh * 62116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business. 72116Sjkh * Permission to use, copy, modify, and distribute this 88870Srgrimes * software is freely granted, provided that this notice 92116Sjkh * is preserved. 102116Sjkh * ==================================================== 112116Sjkh */ 122116Sjkh 132116Sjkh#ifndef lint 1450476Speterstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/s_scalbn.c 117912 2003-07-23 04:53:47Z peter $"; 152116Sjkh#endif 162116Sjkh 178870Srgrimes/* 182116Sjkh * scalbn (double x, int n) 198870Srgrimes * scalbn(x,n) returns x* 2**n computed by exponent 208870Srgrimes * manipulation rather than by actually performing an 212116Sjkh * exponentiation or a multiplication. 222116Sjkh */ 232116Sjkh 242116Sjkh#include "math.h" 252116Sjkh#include "math_private.h" 262116Sjkh 272116Sjkhstatic const double 282116Sjkhtwo54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 292116Sjkhtwom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 302116Sjkhhuge = 1.0e+300, 312116Sjkhtiny = 1.0e-300; 322116Sjkh 3397413Salfreddouble 34117912Speterscalbn (double x, int n) 352116Sjkh{ 362116Sjkh int32_t k,hx,lx; 372116Sjkh EXTRACT_WORDS(hx,lx,x); 382116Sjkh k = (hx&0x7ff00000)>>20; /* extract exponent */ 392116Sjkh if (k==0) { /* 0 or subnormal x */ 402116Sjkh if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 418870Srgrimes x *= two54; 422116Sjkh GET_HIGH_WORD(hx,x); 438870Srgrimes k = ((hx&0x7ff00000)>>20) - 54; 442116Sjkh if (n< -50000) return tiny*x; /*underflow*/ 452116Sjkh } 462116Sjkh if (k==0x7ff) return x+x; /* NaN or Inf */ 478870Srgrimes k = k+n; 482116Sjkh if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ 492116Sjkh if (k > 0) /* normal result */ 502116Sjkh {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 512116Sjkh if (k <= -54) 522116Sjkh if (n > 50000) /* in case integer overflow in n+k */ 532116Sjkh return huge*copysign(huge,x); /*overflow*/ 542116Sjkh else return tiny*copysign(tiny,x); /*underflow*/ 552116Sjkh k += 54; /* subnormal result */ 562116Sjkh SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 572116Sjkh return x*twom54; 582116Sjkh} 59