1 /* @(#)s_scalbn.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 /* 14 * scalbn (double x, int n) 15 * scalbn(x,n) returns x* 2**n computed by exponent 16 * manipulation rather than by actually performing an 17 * exponentiation or a multiplication. 18 */ 19 20 #include <sys/cdefs.h> 21 #include <float.h> 22 #include <math.h> 23 24 #include "math_private.h" 25 26 static const double 27 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 28 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 29 huge = 1.0e+300, 30 tiny = 1.0e-300; 31 32 double 33 scalbn (double x, int n) 34 { 35 int32_t k,hx,lx; 36 EXTRACT_WORDS(hx,lx,x); 37 k = (hx&0x7ff00000)>>20; /* extract exponent */ 38 if (k==0) { /* 0 or subnormal x */ 39 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 40 x *= two54; 41 GET_HIGH_WORD(hx,x); 42 k = ((hx&0x7ff00000)>>20) - 54; 43 if (n< -50000) return tiny*x; /*underflow*/ 44 } 45 if (k==0x7ff) return x+x; /* NaN or Inf */ 46 k = k+n; 47 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ 48 if (k > 0) /* normal result */ 49 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 50 if (k <= -54) 51 if (n > 50000) /* in case integer overflow in n+k */ 52 return huge*copysign(huge,x); /*overflow*/ 53 else return tiny*copysign(tiny,x); /*underflow*/ 54 k += 54; /* subnormal result */ 55 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 56 return x*twom54; 57 } 58 59 #if LDBL_MANT_DIG == 53 60 #ifdef __weak_alias 61 __weak_alias(scalbnl, scalbn); 62 #endif /* __weak_alias */ 63 #endif /* LDBL_MANT_DIG == 53 */ 64