The Android Open Source Project | b07e1d9 | 2009-03-03 19:29:30 -0800 | [diff] [blame] | 1 | |
| 2 | /* @(#)s_scalbn.c 1.3 95/01/18 */ |
| 3 | /* |
| 4 | * ==================================================== |
| 5 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 6 | * |
| 7 | * Developed at SunSoft, a Sun Microsystems, Inc. business. |
| 8 | * Permission to use, copy, modify, and distribute this |
| 9 | * software is freely granted, provided that this notice |
| 10 | * is preserved. |
| 11 | * ==================================================== |
| 12 | */ |
| 13 | |
| 14 | /* |
| 15 | * ieee_scalbn (double x, int n) |
| 16 | * ieee_scalbn(x,n) returns x* 2**n computed by exponent |
| 17 | * manipulation rather than by actually performing an |
| 18 | * exponentiation or a multiplication. |
| 19 | */ |
| 20 | |
| 21 | #include "fdlibm.h" |
| 22 | |
| 23 | #ifdef __STDC__ |
| 24 | static const double |
| 25 | #else |
| 26 | static double |
| 27 | #endif |
| 28 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
| 29 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
| 30 | huge = 1.0e+300, |
| 31 | tiny = 1.0e-300; |
| 32 | |
| 33 | #ifdef __STDC__ |
| 34 | double ieee_scalbn (double x, int n) |
| 35 | #else |
| 36 | double ieee_scalbn (x,n) |
| 37 | double x; int n; |
| 38 | #endif |
| 39 | { |
| 40 | int k,hx,lx; |
| 41 | hx = __HI(x); |
| 42 | lx = __LO(x); |
| 43 | k = (hx&0x7ff00000)>>20; /* extract exponent */ |
| 44 | if (k==0) { /* 0 or subnormal x */ |
| 45 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ |
| 46 | x *= two54; |
| 47 | hx = __HI(x); |
| 48 | k = ((hx&0x7ff00000)>>20) - 54; |
| 49 | if (n< -50000) return tiny*x; /*underflow*/ |
| 50 | } |
| 51 | if (k==0x7ff) return x+x; /* NaN or Inf */ |
| 52 | k = k+n; |
| 53 | if (k > 0x7fe) return huge*ieee_copysign(huge,x); /* overflow */ |
| 54 | if (k > 0) /* normal result */ |
| 55 | {__HI(x) = (hx&0x800fffff)|(k<<20); return x;} |
| 56 | if (k <= -54) |
| 57 | if (n > 50000) /* in case integer overflow in n+k */ |
| 58 | return huge*ieee_copysign(huge,x); /*overflow*/ |
| 59 | else return tiny*ieee_copysign(tiny,x); /*underflow*/ |
| 60 | k += 54; /* subnormal result */ |
| 61 | __HI(x) = (hx&0x800fffff)|(k<<20); |
| 62 | return x*twom54; |
| 63 | } |