diff options
Diffstat (limited to 'sysdeps/ieee754/flt-32/e_log2f.c')
| -rw-r--r-- | sysdeps/ieee754/flt-32/e_log2f.c | 157 |
1 files changed, 83 insertions, 74 deletions
diff --git a/sysdeps/ieee754/flt-32/e_log2f.c b/sysdeps/ieee754/flt-32/e_log2f.c index 857d13fb9b..62edc59cde 100644 --- a/sysdeps/ieee754/flt-32/e_log2f.c +++ b/sysdeps/ieee754/flt-32/e_log2f.c @@ -1,86 +1,95 @@ -/* e_logf.c -- float version of e_log.c. - * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. - * adapted for log2 by Ulrich Drepper <drepper@cygnus.com> - */ +/* Single-precision log2 function. + Copyright (C) 2017-2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. -/* - * ==================================================== - * 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. - * ==================================================== - */ + 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.h> -#include <math_private.h> -#include <fix-int-fp-convert-zero.h> +#include <stdint.h> +#include <shlib-compat.h> +#include <libm-alias-float.h> +#include "math_config.h" + +/* +LOG2F_TABLE_BITS = 4 +LOG2F_POLY_ORDER = 4 -static const float -ln2 = 0.69314718055994530942, -two25 = 3.355443200e+07, /* 0x4c000000 */ -Lg1 = 6.6666668653e-01, /* 3F2AAAAB */ -Lg2 = 4.0000000596e-01, /* 3ECCCCCD */ -Lg3 = 2.8571429849e-01, /* 3E924925 */ -Lg4 = 2.2222198546e-01, /* 3E638E29 */ -Lg5 = 1.8183572590e-01, /* 3E3A3325 */ -Lg6 = 1.5313838422e-01, /* 3E1CD04F */ -Lg7 = 1.4798198640e-01; /* 3E178897 */ +ULP error: 0.752 (nearest rounding.) +Relative error: 1.9 * 2^-26 (before rounding.) +*/ -static const float zero = 0.0; +#define N (1 << LOG2F_TABLE_BITS) +#define T __log2f_data.tab +#define A __log2f_data.poly +#define OFF 0x3f330000 float -__ieee754_log2f(float x) +__log2f (float x) { - float hfsq,f,s,z,R,w,t1,t2,dk; - int32_t k,ix,i,j; + /* double_t for better performance on targets with FLT_EVAL_METHOD==2. */ + double_t z, r, r2, p, y, y0, invc, logc; + uint32_t ix, iz, top, tmp; + int k, i; + + ix = asuint (x); +#if WANT_ROUNDING + /* Fix sign of zero with downward rounding when x==1. */ + if (__glibc_unlikely (ix == 0x3f800000)) + return 0; +#endif + if (__glibc_unlikely (ix - 0x00800000 >= 0x7f800000 - 0x00800000)) + { + /* x < 0x1p-126 or inf or nan. */ + if (ix * 2 == 0) + return __math_divzerof (1); + if (ix == 0x7f800000) /* log2(inf) == inf. */ + return x; + if ((ix & 0x80000000) || ix * 2 >= 0xff000000) + return __math_invalidf (x); + /* x is subnormal, normalize it. */ + ix = asuint (x * 0x1p23f); + ix -= 23 << 23; + } + + /* x = 2^k z; where z is in range [OFF,2*OFF] and exact. + The range is split into N subintervals. + The ith subinterval contains z and c is near its center. */ + tmp = ix - OFF; + i = (tmp >> (23 - LOG2F_TABLE_BITS)) % N; + top = tmp & 0xff800000; + iz = ix - top; + k = (int32_t) tmp >> 23; /* arithmetic shift */ + invc = T[i].invc; + logc = T[i].logc; + z = (double_t) asfloat (iz); - GET_FLOAT_WORD(ix,x); + /* log2(x) = log1p(z/c-1)/ln2 + log2(c) + k */ + r = z * invc - 1; + y0 = logc + (double_t) k; - k=0; - if (ix < 0x00800000) { /* x < 2**-126 */ - if (__builtin_expect((ix&0x7fffffff)==0, 0)) - return -two25/(x-x); /* log(+-0)=-inf */ - if (__builtin_expect(ix<0, 0)) - return (x-x)/(x-x); /* log(-#) = NaN */ - k -= 25; x *= two25; /* subnormal number, scale up x */ - GET_FLOAT_WORD(ix,x); - } - if (__builtin_expect(ix >= 0x7f800000, 0)) return x+x; - k += (ix>>23)-127; - ix &= 0x007fffff; - i = (ix+(0x95f64<<3))&0x800000; - SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */ - k += (i>>23); - dk = (float)k; - f = x-(float)1.0; - if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */ - if(f==zero) - { - if (FIX_INT_FP_CONVERT_ZERO && dk == 0.0f) - dk = 0.0f; - return dk; - } - R = f*f*((float)0.5-(float)0.33333333333333333*f); - return dk-(R-f)/ln2; - } - s = f/((float)2.0+f); - z = s*s; - i = ix-(0x6147a<<3); - w = z*z; - j = (0x6b851<<3)-ix; - t1= w*(Lg2+w*(Lg4+w*Lg6)); - t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7))); - i |= j; - R = t2+t1; - if(i>0) { - hfsq=(float)0.5*f*f; - return dk-((hfsq-(s*(hfsq+R)))-f)/ln2; - } else { - return dk-((s*(f-R))-f)/ln2; - } + /* Pipelined polynomial evaluation to approximate log1p(r)/ln2. */ + r2 = r * r; + y = A[1] * r + A[2]; + y = A[0] * r2 + y; + p = A[3] * r + y0; + y = y * r2 + p; + return (float) y; } -strong_alias (__ieee754_log2f, __log2f_finite) +#ifndef __log2f +strong_alias (__log2f, __ieee754_log2f) +strong_alias (__log2f, __log2f_finite) +versioned_symbol (libm, __log2f, log2f, GLIBC_2_27); +libm_alias_float_other (__log2, log2) +#endif |