| /* @(#)s_ilogb.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 char rcsid[] = "$NetBSD: s_ilogb.c,v 1.9 1995/05/10 20:47:28 jtc Exp $"; |
| #endif |
| |
| /* ilogb(double x) |
| * return the binary exponent of non-zero x |
| * ilogb(0) = FP_ILOGB0 |
| * ilogb(NaN) = FP_ILOGBNAN (no signal is raised) |
| * ilogb(+-Inf) = INT_MAX (no signal is raised) |
| */ |
| |
| #include <limits.h> |
| #include <math.h> |
| #include <math_private.h> |
| |
| int |
| __ieee754_ilogb (double x) |
| { |
| int32_t hx, lx, ix; |
| |
| GET_HIGH_WORD (hx, x); |
| hx &= 0x7fffffff; |
| if (hx < 0x00100000) |
| { |
| GET_LOW_WORD (lx, x); |
| if ((hx | lx) == 0) |
| return FP_ILOGB0; /* ilogb(0) = FP_ILOGB0 */ |
| else /* subnormal x */ |
| if (hx == 0) |
| { |
| for (ix = -1043; lx > 0; lx <<= 1) |
| ix -= 1; |
| } |
| else |
| { |
| for (ix = -1022, hx <<= 11; hx > 0; hx <<= 1) |
| ix -= 1; |
| } |
| return ix; |
| } |
| else if (hx < 0x7ff00000) |
| return (hx >> 20) - 1023; |
| else if (FP_ILOGBNAN != INT_MAX) |
| { |
| /* ISO C99 requires ilogb(+-Inf) == INT_MAX. */ |
| GET_LOW_WORD (lx, x); |
| if (((hx ^ 0x7ff00000) | lx) == 0) |
| return INT_MAX; |
| } |
| return FP_ILOGBNAN; |
| } |
