| /* logb(). PowerPC/POWER7 version. |
| Copyright (C) 2012-2014 Free Software Foundation, Inc. |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <math_ldbl_opt.h> |
| |
| /* This implementation avoids FP to INT conversions by using VSX |
| bitwise instructions over FP values. */ |
| |
| static const double two1div52 = 2.220446049250313e-16; /* 1/2**52 */ |
| static const double two10m1 = -1023.0; /* 2**10 -1 */ |
| |
| /* FP mask to extract the exponent. */ |
| static const union { |
| unsigned long long mask; |
| double d; |
| } mask = { 0x7ff0000000000000ULL }; |
| |
| double |
| __logb (double x) |
| { |
| double ret; |
| |
| if (__builtin_expect (x == 0.0, 0)) |
| /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF]. */ |
| return -1.0 / __builtin_fabs (x); |
| |
| /* ret = x & 0x7ff0000000000000; */ |
| asm ( |
| "xxland %x0,%x1,%x2\n" |
| "fcfid %0,%0" |
| : "=f" (ret) |
| : "f" (x), "f" (mask.d)); |
| /* ret = (ret >> 52) - 1023.0; */ |
| ret = (ret * two1div52) + two10m1; |
| if (__builtin_expect (ret > -two10m1, 0)) |
| /* Multiplication is used to set logb (+-INF) = INF. */ |
| return (x * x); |
| else if (__builtin_expect (ret == two10m1, 0)) |
| { |
| /* POSIX specifies that denormal numbers are treated as |
| though they were normalized. */ |
| int32_t lx, ix; |
| int ma; |
| |
| EXTRACT_WORDS (ix, lx, x); |
| if (ix == 0) |
| ma = __builtin_clz (lx) + 32; |
| else |
| ma = __builtin_clz (ix); |
| return (double) (-1023 - (ma - 12)); |
| } |
| /* Test to avoid logb_downward (0.0) == -0.0. */ |
| return ret == -0.0 ? 0.0 : ret; |
| } |
| weak_alias (__logb, logb) |
| #ifdef NO_LONG_DOUBLE |
| strong_alias (__logb, __logbl) |
| weak_alias (__logb, logbl) |
| #endif |
| |
| #if LONG_DOUBLE_COMPAT (libm, GLIBC_2_0) |
| compat_symbol (libm, logb, logbl, GLIBC_2_0); |
| #endif |
