| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* |
| 2 | * ==================================================== |
| 3 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
| 4 | * |
| 5 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
| 6 | * Permission to use, copy, modify, and distribute this |
| 7 | * software is freely granted, provided that this notice |
| 8 | * is preserved. |
| 9 | * ==================================================== |
| 10 | */ |
| 11 | |
| 12 | /* ilogb(double x) |
| 13 | * return the binary exponent of x |
| 14 | * ilogb(+-0) = FP_ILOGB0 |
| 15 | * ilogb(+-inf) = INT_MAX |
| 16 | * ilogb(NaN) = FP_ILOGBNAN (no signal is raised) |
| 17 | */ |
| 18 | |
| 19 | #include "math.h" |
| 20 | #include "math_private.h" |
| 21 | |
| 22 | int ilogb(double x) |
| 23 | { |
| 24 | int32_t hx,lx,ix; |
| 25 | |
| 26 | GET_HIGH_WORD(hx, x); |
| 27 | hx &= 0x7fffffff; |
| 28 | |
| 29 | if (hx < 0x00100000) { |
| 30 | GET_LOW_WORD(lx, x); |
| 31 | if ((hx|lx)==0) /* +-0, ilogb(0) = FP_ILOGB0 */ |
| 32 | return FP_ILOGB0; |
| 33 | /* subnormal x */ |
| 34 | ix = -1043; |
| 35 | if (hx != 0) { |
| 36 | ix = -1022; |
| 37 | lx = (hx << 11); |
| 38 | } |
| 39 | /* each leading zero mantissa bit makes exponent smaller */ |
| 40 | for (; lx > 0; lx <<= 1) |
| 41 | ix--; |
| 42 | return ix; |
| 43 | } |
| 44 | |
| 45 | if (hx < 0x7ff00000) /* normal x */ |
| 46 | return (hx>>20) - 1023; |
| 47 | |
| 48 | if (FP_ILOGBNAN != (~0U >> 1)) { |
| 49 | GET_LOW_WORD(lx, x); |
| 50 | if (hx == 0x7ff00000 && lx == 0) /* +-inf */ |
| 51 | return ~0U >> 1; /* = INT_MAX */ |
| 52 | } |
| 53 | |
| 54 | /* NAN. ilogb(NAN) = FP_ILOGBNAN */ |
| 55 | return FP_ILOGBNAN; |
| 56 | } |
| 57 | libm_hidden_def(ilogb) |