| /* |
| * ==================================================== |
| * 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> |
| |
| static const double |
| two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
| twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
| huge = 1.0e+300, |
| tiny = 1.0e-300; |
| |
| double |
| __scalbn (double x, int n) |
| { |
| int32_t k, hx, lx; |
| EXTRACT_WORDS (hx, lx, x); |
| k = (hx & 0x7ff00000) >> 20; /* extract exponent */ |
| if (__builtin_expect (k == 0, 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 (__builtin_expect (k == 0x7ff, 0)) |
| return x + x; /* NaN or Inf */ |
| if (__builtin_expect (n < -50000, 0)) |
| return tiny * __copysign (tiny, x); /*underflow*/ |
| if (__builtin_expect (n > 50000 || k + n > 0x7fe, 0)) |
| return huge * __copysign (huge, x); /* overflow */ |
| /* Now k and n are bounded we know that k = k+n does not |
| overflow. */ |
| k = k + n; |
| if (__builtin_expect (k > 0, 1)) /* normal result */ |
| { |
| SET_HIGH_WORD (x, (hx & 0x800fffff) | (k << 20)); return x; |
| } |
| if (k <= -54) |
| return tiny * __copysign (tiny, x); /*underflow*/ |
| k += 54; /* subnormal result */ |
| SET_HIGH_WORD (x, (hx & 0x800fffff) | (k << 20)); |
| return x * twom54; |
| } |
| weak_alias (__scalbn, scalbn) |
| #ifdef NO_LONG_DOUBLE |
| strong_alias (__scalbn, __scalbnl) |
| weak_alias (__scalbn, scalbnl) |
| #endif |
