| /* @(#)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. |
| * ==================================================== |
| */ |
| |
| /* |
| * 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 "math.h" |
| #include "math_private.h" |
| |
| #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 |
| { |
| int64_t ix; |
| int64_t k; |
| EXTRACT_WORDS64(ix,x); |
| k = (ix >> 52) & 0x7ff; /* extract exponent */ |
| if (k==0) { /* 0 or subnormal x */ |
| if ((ix & UINT64_C(0xfffffffffffff))==0) return x; /* +-0 */ |
| x *= two54; |
| EXTRACT_WORDS64(ix,x); |
| k = ((ix >> 52) & 0x7ff) - 54; |
| } |
| if (k==0x7ff) return x+x; /* NaN or Inf */ |
| k = k+n; |
| if (n> 50000 || k > 0x7fe) |
| return huge*__copysign(huge,x); /* overflow */ |
| if (n< -50000) return tiny*__copysign(tiny,x); /*underflow*/ |
| if (k > 0) /* normal result */ |
| {INSERT_WORDS64(x,(ix&UINT64_C(0x800fffffffffffff))|(k<<52)); |
| return x;} |
| if (k <= -54) |
| return tiny*__copysign(tiny,x); /*underflow*/ |
| k += 54; /* subnormal result */ |
| INSERT_WORDS64(x,(ix&INT64_C(0x800fffffffffffff))|(k<<52)); |
| return x*twom54; |
| } |
| weak_alias (__scalbn, scalbn) |
| #ifdef NO_LONG_DOUBLE |
| strong_alias (__scalbn, __scalbnl) |
| weak_alias (__scalbn, scalbnl) |
| #endif |
