forked from KolibriOS/kolibrios
120 lines
3.1 KiB
C
120 lines
3.1 KiB
C
/*
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dither: Generate shaped noise for dithering
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copyright 2009 by the mpg123 project - free software under the terms of the LGPL 2.1
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see COPYING and AUTHORS files in distribution or http://mpg123.org
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initially written by Taihei Monma
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*/
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#include "config.h"
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#include "compat.h"
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#include "dither.h"
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static const uint32_t init_seed = 2463534242UL;
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#define LAP 100
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/*
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xorshift random number generator, with output scaling to [-0.5, 0.5]
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This is the white noise...
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See http://www.jstatsoft.org/v08/i14/paper on XOR shift random number generators.
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*/
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static float rand_xorshift32(uint32_t *seed)
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{
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union
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{
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uint32_t i;
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float f;
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} fi;
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fi.i = *seed;
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fi.i ^= (fi.i<<13);
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fi.i ^= (fi.i>>17);
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fi.i ^= (fi.i<<5);
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*seed = fi.i;
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/* scale the number to [-0.5, 0.5] */
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#ifdef IEEE_FLOAT
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fi.i = (fi.i>>9)|0x3f800000;
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fi.f -= 1.5f;
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#else
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fi.f = (double)fi.i / 4294967295.0;
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fi.f -= 0.5f;
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#endif
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return fi.f;
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}
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static void white_noise(float *table, size_t count)
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{
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size_t i;
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uint32_t seed = init_seed;
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for(i=0; i<count; ++i)
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table[i] = rand_xorshift32(&seed);
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}
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static void tpdf_noise(float *table, size_t count)
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{
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size_t i;
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uint32_t seed = init_seed;
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for(i=0; i<count; ++i)
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table[i] = rand_xorshift32(&seed) + rand_xorshift32(&seed);
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}
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static void highpass_tpdf_noise(float *table, size_t count)
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{
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size_t i;
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uint32_t seed = init_seed;
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/* Ensure some minimum lap for keeping the high-pass filter circular. */
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size_t lap = count > 2*LAP ? LAP : count/2;
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float input_noise;
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float xv[9], yv[9];
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for(i=0;i<9;i++)
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{
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xv[i] = yv[i] = 0.0f;
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}
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for(i=0;i<count+lap;i++)
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{
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if(i==count) seed=init_seed;
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/* generate and add 2 random numbers, to make a TPDF noise distribution */
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input_noise = rand_xorshift32(&seed) + rand_xorshift32(&seed);
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/* apply 8th order Chebyshev high-pass IIR filter */
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/* Coefficients are from http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html
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Given parameters are: Chebyshev, Highpass, ripple=-1, order=8, samplerate=44100, corner1=19000 */
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xv[0] = xv[1]; xv[1] = xv[2]; xv[2] = xv[3]; xv[3] = xv[4]; xv[4] = xv[5]; xv[5] = xv[6]; xv[6] = xv[7]; xv[7] = xv[8];
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xv[8] = input_noise / 1.382814179e+07;
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yv[0] = yv[1]; yv[1] = yv[2]; yv[2] = yv[3]; yv[3] = yv[4]; yv[4] = yv[5]; yv[5] = yv[6]; yv[6] = yv[7]; yv[7] = yv[8];
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yv[8] = (xv[0] + xv[8]) - 8 * (xv[1] + xv[7]) + 28 * (xv[2] + xv[6])
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- 56 * (xv[3] + xv[5]) + 70 * xv[4]
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+ ( -0.6706204984 * yv[0]) + ( -5.3720827038 * yv[1])
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+ (-19.0865382480 * yv[2]) + (-39.2831607860 * yv[3])
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+ (-51.2308985070 * yv[4]) + (-43.3590135780 * yv[5])
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+ (-23.2632305320 * yv[6]) + ( -7.2370122050 * yv[7]);
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if(i>=lap) table[i-lap] = yv[8] * 3.0f;
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}
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}
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void mpg123_noise(float* table, size_t count, enum mpg123_noise_type noisetype)
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{
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switch(noisetype)
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{
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case mpg123_white_noise: white_noise(table, count); break;
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case mpg123_tpdf_noise: tpdf_noise(table, count); break;
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case mpg123_highpass_tpdf_noise:
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highpass_tpdf_noise(table, count);
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break;
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}
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}
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/* Generate white noise and shape it with a high pass filter. */
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void dither_table_init(float *dithertable)
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{
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highpass_tpdf_noise(dithertable, DITHERSIZE);
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}
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