mirror of git://sourceware.org/git/glibc.git
New generic log2f
Similar to the new logf: double precision arithmetics and a small lookup table is used. The argument reduction step is the same as in the new logf. without wrapper on aarch64: log2f reciprocal-throughput: 2.3x faster log2f latency: 2.1x faster old worst case error: 1.72 ulp new worst case error: 0.75 ulp aarch64 .text size: -252 bytes aarch64 .rodata size: +244 bytes * math/Makefile (type-float-routines): Add e_log2f_data. * sysdeps/ieee754/flt-32/e_log2f.c: New implementation. * sysdeps/ieee754/flt-32/e_log2f_data.c: New file. * sysdeps/ieee754/flt-32/math_config.h (__log2f_data): Define. (LOG2F_TABLE_BITS, LOG2F_POLY_ORDER): Define. * sysdeps/i386/fpu/e_log2f_data.c: New file. * sysdeps/ia64/fpu/e_log2f_data.c: New file. * sysdeps/m68k/m680x0/fpu/e_log2f_data.c: New file.
This commit is contained in:
Szabolcs Nagy
parent
90c42e40d0
commit
875c76c704
11
ChangeLog
11
ChangeLog
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@ -1,3 +1,14 @@
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2017-09-29 Szabolcs Nagy <szabolcs.nagy@arm.com>
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* math/Makefile (type-float-routines): Add e_log2f_data.
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* sysdeps/ieee754/flt-32/e_log2f.c: New implementation.
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* sysdeps/ieee754/flt-32/e_log2f_data.c: New file.
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* sysdeps/ieee754/flt-32/math_config.h (__log2f_data): Define.
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(LOG2F_TABLE_BITS, LOG2F_POLY_ORDER): Define.
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* sysdeps/i386/fpu/e_log2f_data.c: New file.
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* sysdeps/ia64/fpu/e_log2f_data.c: New file.
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* sysdeps/m68k/m680x0/fpu/e_log2f_data.c: New file.
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2017-09-29 Szabolcs Nagy <szabolcs.nagy@arm.com>
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* math/Makefile (type-float-routines): Add e_logf_data.
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2
NEWS
2
NEWS
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@ -14,7 +14,7 @@ Major new features:
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* Optimized x86-64 trunc and truncf for processors with SSE4.1.
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* Optimized generic expf, exp2f, logf.
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* Optimized generic expf, exp2f, logf, log2f.
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* In order to support faster and safer process termination the malloc API
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family of functions will no longer print a failure address and stack
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@ -115,7 +115,8 @@ type-double-routines := branred doasin dosincos halfulp mpa mpatan2 \
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# float support
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type-float-suffix := f
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type-float-routines := k_rem_pio2f math_errf e_exp2f_data e_logf_data
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type-float-routines := k_rem_pio2f math_errf e_exp2f_data e_logf_data \
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e_log2f_data
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# _Float128 support
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type-float128-suffix := f128
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@ -0,0 +1 @@
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/* Not needed. */
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@ -0,0 +1 @@
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/* Not needed. */
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@ -1,86 +1,88 @@
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/* e_logf.c -- float version of e_log.c.
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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* adapted for log2 by Ulrich Drepper <drepper@cygnus.com>
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*/
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/* Single-precision log2 function.
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Copyright (C) 2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <math_private.h>
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#include <fix-int-fp-convert-zero.h>
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#include <stdint.h>
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#include "math_config.h"
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static const float
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ln2 = 0.69314718055994530942,
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two25 = 3.355443200e+07, /* 0x4c000000 */
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Lg1 = 6.6666668653e-01, /* 3F2AAAAB */
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Lg2 = 4.0000000596e-01, /* 3ECCCCCD */
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Lg3 = 2.8571429849e-01, /* 3E924925 */
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Lg4 = 2.2222198546e-01, /* 3E638E29 */
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Lg5 = 1.8183572590e-01, /* 3E3A3325 */
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Lg6 = 1.5313838422e-01, /* 3E1CD04F */
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Lg7 = 1.4798198640e-01; /* 3E178897 */
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/*
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LOG2F_TABLE_BITS = 4
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LOG2F_POLY_ORDER = 4
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static const float zero = 0.0;
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ULP error: 0.752 (nearest rounding.)
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Relative error: 1.9 * 2^-26 (before rounding.)
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*/
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#define N (1 << LOG2F_TABLE_BITS)
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#define T __log2f_data.tab
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#define A __log2f_data.poly
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#define OFF 0x3f330000
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float
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__ieee754_log2f(float x)
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__ieee754_log2f (float x)
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{
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float hfsq,f,s,z,R,w,t1,t2,dk;
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int32_t k,ix,i,j;
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/* double_t for better performance on targets with FLT_EVAL_METHOD==2. */
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double_t z, r, r2, p, y, y0, invc, logc;
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uint32_t ix, iz, top, tmp;
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int k, i;
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GET_FLOAT_WORD(ix,x);
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ix = asuint (x);
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#if WANT_ROUNDING
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/* Fix sign of zero with downward rounding when x==1. */
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if (__glibc_unlikely (ix == 0x3f800000))
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return 0;
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#endif
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if (__glibc_unlikely (ix - 0x00800000 >= 0x7f800000 - 0x00800000))
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{
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/* x < 0x1p-126 or inf or nan. */
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if (ix * 2 == 0)
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return __math_divzerof (1);
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if (ix == 0x7f800000) /* log2(inf) == inf. */
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return x;
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if ((ix & 0x80000000) || ix * 2 >= 0xff000000)
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return __math_invalidf (x);
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/* x is subnormal, normalize it. */
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ix = asuint (x * 0x1p23f);
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ix -= 23 << 23;
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}
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k=0;
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if (ix < 0x00800000) { /* x < 2**-126 */
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if (__builtin_expect((ix&0x7fffffff)==0, 0))
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return -two25/__fabsf (x); /* log(+-0)=-inf */
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if (__builtin_expect(ix<0, 0))
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return (x-x)/(x-x); /* log(-#) = NaN */
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k -= 25; x *= two25; /* subnormal number, scale up x */
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GET_FLOAT_WORD(ix,x);
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}
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if (__builtin_expect(ix >= 0x7f800000, 0)) return x+x;
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k += (ix>>23)-127;
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ix &= 0x007fffff;
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i = (ix+(0x95f64<<3))&0x800000;
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SET_FLOAT_WORD(x,ix|(i^0x3f800000)); /* normalize x or x/2 */
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k += (i>>23);
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dk = (float)k;
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f = x-(float)1.0;
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if((0x007fffff&(15+ix))<16) { /* |f| < 2**-20 */
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if(f==zero)
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{
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if (FIX_INT_FP_CONVERT_ZERO && dk == 0.0f)
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dk = 0.0f;
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return dk;
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}
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R = f*f*((float)0.5-(float)0.33333333333333333*f);
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return dk-(R-f)/ln2;
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}
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s = f/((float)2.0+f);
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z = s*s;
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i = ix-(0x6147a<<3);
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w = z*z;
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j = (0x6b851<<3)-ix;
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t1= w*(Lg2+w*(Lg4+w*Lg6));
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t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
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i |= j;
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R = t2+t1;
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if(i>0) {
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hfsq=(float)0.5*f*f;
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return dk-((hfsq-(s*(hfsq+R)))-f)/ln2;
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} else {
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return dk-((s*(f-R))-f)/ln2;
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}
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/* x = 2^k z; where z is in range [OFF,2*OFF] and exact.
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The range is split into N subintervals.
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The ith subinterval contains z and c is near its center. */
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tmp = ix - OFF;
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i = (tmp >> (23 - LOG2F_TABLE_BITS)) % N;
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top = tmp & 0xff800000;
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iz = ix - top;
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k = (int32_t) tmp >> 23; /* arithmetic shift */
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invc = T[i].invc;
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logc = T[i].logc;
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z = (double_t) asfloat (iz);
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/* log2(x) = log1p(z/c-1)/ln2 + log2(c) + k */
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r = z * invc - 1;
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y0 = logc + (double_t) k;
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/* Pipelined polynomial evaluation to approximate log1p(r)/ln2. */
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r2 = r * r;
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y = A[1] * r + A[2];
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y = A[0] * r2 + y;
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p = A[3] * r + y0;
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y = y * r2 + p;
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return (float) y;
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}
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strong_alias (__ieee754_log2f, __log2f_finite)
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@ -0,0 +1,44 @@
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/* Data definition for log2f.
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Copyright (C) 2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include "math_config.h"
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const struct log2f_data __log2f_data = {
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.tab = {
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{ 0x1.661ec79f8f3bep+0, -0x1.efec65b963019p-2 },
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{ 0x1.571ed4aaf883dp+0, -0x1.b0b6832d4fca4p-2 },
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{ 0x1.49539f0f010bp+0, -0x1.7418b0a1fb77bp-2 },
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{ 0x1.3c995b0b80385p+0, -0x1.39de91a6dcf7bp-2 },
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{ 0x1.30d190c8864a5p+0, -0x1.01d9bf3f2b631p-2 },
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{ 0x1.25e227b0b8eap+0, -0x1.97c1d1b3b7afp-3 },
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{ 0x1.1bb4a4a1a343fp+0, -0x1.2f9e393af3c9fp-3 },
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{ 0x1.12358f08ae5bap+0, -0x1.960cbbf788d5cp-4 },
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{ 0x1.0953f419900a7p+0, -0x1.a6f9db6475fcep-5 },
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{ 0x1p+0, 0x0p+0 },
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{ 0x1.e608cfd9a47acp-1, 0x1.338ca9f24f53dp-4 },
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{ 0x1.ca4b31f026aap-1, 0x1.476a9543891bap-3 },
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{ 0x1.b2036576afce6p-1, 0x1.e840b4ac4e4d2p-3 },
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{ 0x1.9c2d163a1aa2dp-1, 0x1.40645f0c6651cp-2 },
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{ 0x1.886e6037841edp-1, 0x1.88e9c2c1b9ff8p-2 },
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{ 0x1.767dcf5534862p-1, 0x1.ce0a44eb17bccp-2 },
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},
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.poly = {
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-0x1.712b6f70a7e4dp-2, 0x1.ecabf496832ep-2, -0x1.715479ffae3dep-1,
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0x1.715475f35c8b8p0,
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}
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};
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@ -123,4 +123,15 @@ extern const struct logf_data
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double poly[LOGF_POLY_ORDER - 1]; /* First order coefficient is 1. */
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} __logf_data attribute_hidden;
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#define LOG2F_TABLE_BITS 4
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#define LOG2F_POLY_ORDER 4
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extern const struct log2f_data
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{
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struct
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{
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double invc, logc;
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} tab[1 << LOG2F_TABLE_BITS];
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double poly[LOG2F_POLY_ORDER];
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} __log2f_data attribute_hidden;
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#endif
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@ -0,0 +1 @@
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/* Not needed. */
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