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https://github.com/libretro/RetroArch
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136 lines
3.5 KiB
C
136 lines
3.5 KiB
C
/*
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The MIT License (MIT)
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Copyright (c) 2015 Lachlan Tychsen-Smith (lachlan.ts@gmail.com)
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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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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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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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/*
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Based on:
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log10(x) = log10((1+m) * (2^n))
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log(x) = n * log10(2) + log10(1 + m)
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log(1+m) = Poly(1+m)
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where Poly(x) is the Minimax approximation of log10(x) over the
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range [1, 2]
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Test func : log10f(x)
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Test Range: 1 < x < 10000
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Peak Error: ~0.000040%
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RMS Error: ~0.000008%
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*/
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#include "math.h"
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#include "math_neon.h"
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const float __log10f_rng = 0.3010299957f;
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const float __log10f_lut[8] = {
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-0.99697286229624, //p0
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-1.07301643912502, //p4
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-2.46980061535534, //p2
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-0.07176870463131, //p6
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2.247870219989470, //p1
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0.366547581117400, //p5
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1.991005185100089, //p3
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0.006135635201050, //p7
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};
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float log10f_c(float x)
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{
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float a, b, c, d, xx;
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int m;
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union {
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float f;
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int i;
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} r;
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//extract exponent
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r.f = x;
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m = (r.i >> 23);
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m = m - 127;
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r.i = r.i - (m << 23);
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//Taylor Polynomial (Estrins)
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xx = r.f * r.f;
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a = (__log10f_lut[4] * r.f) + (__log10f_lut[0]);
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b = (__log10f_lut[6] * r.f) + (__log10f_lut[2]);
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c = (__log10f_lut[5] * r.f) + (__log10f_lut[1]);
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d = (__log10f_lut[7] * r.f) + (__log10f_lut[3]);
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a = a + b * xx;
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c = c + d * xx;
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xx = xx * xx;
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r.f = a + c * xx;
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//add exponent
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r.f = r.f + ((float) m) * __log10f_rng;
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return r.f;
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}
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float log10f_neon_hfp(float x)
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{
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#ifdef __MATH_NEON
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asm volatile (
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"vdup.f32 d0, d0[0] \n\t" //d0 = {x,x};
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//extract exponent
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"vmov.i32 d2, #127 \n\t" //d2 = 127;
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"vshr.u32 d6, d0, #23 \n\t" //d6 = d0 >> 23;
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"vsub.i32 d6, d6, d2 \n\t" //d6 = d6 - d2;
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"vshl.u32 d1, d6, #23 \n\t" //d1 = d6 << 23;
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"vsub.i32 d0, d0, d1 \n\t" //d0 = d0 + d1;
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//polynomial:
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"vmul.f32 d1, d0, d0 \n\t" //d1 = d0*d0 = {x^2, x^2}
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"vld1.32 {d2, d3, d4, d5}, [%1] \n\t" //q1 = {p0, p4, p2, p6}, q2 = {p1, p5, p3, p7} ;
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"vmla.f32 q1, q2, d0[0] \n\t" //q1 = q1 + q2 * d0[0]
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"vmla.f32 d2, d3, d1[0] \n\t" //d2 = d2 + d3 * d1[0]
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"vmul.f32 d1, d1, d1 \n\t" //d1 = d1 * d1 = {x^4, x^4}
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"vmla.f32 d2, d1, d2[1] \n\t" //d2 = d2 + d1 * d2[1]
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//add exponent
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"vdup.32 d7, %0 \n\t" //d7 = {rng, rng}
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"vcvt.f32.s32 d6, d6 \n\t" //d6 = (float) d6
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"vmla.f32 d2, d6, d7 \n\t" //d2 = d2 + d6 * d7
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"vmov.f32 s0, s4 \n\t" //s0 = s4
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:: "r"(__log10f_rng), "r"(__log10f_lut)
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: "d0", "d1", "q1", "q2", "d6", "d7"
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);
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#endif
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}
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float log10f_neon_sfp(float x)
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{
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#ifdef __MATH_NEON
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asm volatile ("vmov.f32 s0, r0 \n\t");
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log10f_neon_hfp(x);
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asm volatile ("vmov.f32 r0, s0 \n\t");
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#else
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return log10f_c(x);
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#endif
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};
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