| /* @(#)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. |
| * ==================================================== |
| */ |
| |
| #if defined(LIBM_SCCS) && !defined(lint) |
| static const char rcsid[] = |
| "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $"; |
| #endif |
| |
| /* |
| * 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_libm.h" |
| #include "math_private.h" |
| |
| libm_hidden_proto(copysign) |
| #ifdef __STDC__ |
| static const double |
| #else |
| static double |
| #endif |
| two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ |
| twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ |
| huge_val = 1.0e+300, tiny = 1.0e-300; |
| |
| libm_hidden_proto(scalbn) |
| #ifdef __STDC__ |
| double scalbn(double x, int n) |
| #else |
| double scalbn(x, n) |
| double x; |
| int n; |
| #endif |
| { |
| int32_t k, hx, lx; |
| EXTRACT_WORDS(hx, lx, x); |
| k = (hx & 0x7ff00000) >> 20; /* extract exponent */ |
| if (k == 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 (n < -50000) |
| return tiny * x; /* underflow */ |
| } |
| if (k == 0x7ff) |
| return x + x; /* NaN or Inf */ |
| k = k + n; |
| if (k > 0x7fe) |
| return huge_val * copysign(huge_val, x); /* overflow */ |
| if (k > 0) { /* normal result */ |
| SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20)); |
| return x; |
| } |
| if (k <= -54) { |
| if (n > 50000) /* in case integer overflow in n+k */ |
| return huge_val * copysign(huge_val, x); /* overflow */ |
| else |
| return tiny * copysign(tiny, x); /* underflow */ |
| } |
| k += 54; /* subnormal result */ |
| SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20)); |
| return x * twom54; |
| } |
| |
| libm_hidden_def(scalbn) |
