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95 lines
3.1 KiB
95 lines
3.1 KiB
4 months ago
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/*
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* Copyright (c) 2014 Advanced Micro Devices, Inc.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#ifdef cl_khr_fp64
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#include <clc/clc.h>
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#include "ep_log.h"
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#include "math.h"
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#include "tables.h"
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#pragma OPENCL EXTENSION cl_khr_fp64 : enable
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#define LN0 8.33333333333317923934e-02
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#define LN1 1.25000000037717509602e-02
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#define LN2 2.23213998791944806202e-03
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#define LN3 4.34887777707614552256e-04
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#define LF0 8.33333333333333593622e-02
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#define LF1 1.24999999978138668903e-02
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#define LF2 2.23219810758559851206e-03
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_CLC_DEF void __clc_ep_log(double x, int *xexp, double *r1, double *r2)
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{
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// Computes natural log(x). Algorithm based on:
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// Ping-Tak Peter Tang
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// "Table-driven implementation of the logarithm function in IEEE
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// floating-point arithmetic"
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// ACM Transactions on Mathematical Software (TOMS)
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// Volume 16, Issue 4 (December 1990)
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int near_one = x >= 0x1.e0faap-1 & x <= 0x1.1082cp+0;
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ulong ux = as_ulong(x);
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ulong uxs = as_ulong(as_double(0x03d0000000000000UL | ux) - 0x1.0p-962);
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int c = ux < IMPBIT_DP64;
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ux = c ? uxs : ux;
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int expadjust = c ? 60 : 0;
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// Store the exponent of x in xexp and put f into the range [0.5,1)
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int xexp1 = ((as_int2(ux).hi >> 20) & 0x7ff) - EXPBIAS_DP64 - expadjust;
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double f = as_double(HALFEXPBITS_DP64 | (ux & MANTBITS_DP64));
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*xexp = near_one ? 0 : xexp1;
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double r = x - 1.0;
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double u1 = MATH_DIVIDE(r, 2.0 + r);
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double ru1 = -r * u1;
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u1 = u1 + u1;
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int index = as_int2(ux).hi >> 13;
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index = ((0x80 | (index & 0x7e)) >> 1) + (index & 0x1);
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double f1 = index * 0x1.0p-7;
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double f2 = f - f1;
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double u2 = MATH_DIVIDE(f2, fma(0.5, f2, f1));
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double2 tv = USE_TABLE(ln_tbl, (index - 64));
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double z1 = tv.s0;
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double q = tv.s1;
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z1 = near_one ? r : z1;
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q = near_one ? 0.0 : q;
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double u = near_one ? u1 : u2;
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double v = u*u;
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double cc = near_one ? ru1 : u2;
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double z21 = fma(v, fma(v, fma(v, LN3, LN2), LN1), LN0);
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double z22 = fma(v, fma(v, LF2, LF1), LF0);
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double z2 = near_one ? z21 : z22;
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z2 = fma(u*v, z2, cc) + q;
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*r1 = z1;
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*r2 = z2;
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}
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#endif
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