chebyshev_int8.py

import array,os,textwrap,math


def chebyTable(outfile, tablename, tablelength, curvenum):
    
    """
    Generates chebyshev polynomial curve tables for WaveShaper.
    
    Args:
        outfile:    The file to save as output.
        tablename:  The name to give the table of converted data in the new file.
        tablelength:    Use a power of two.
        curvenum:   The chebyshev polynomial curve number to chebyTable.
    
    Examples:
        chebyTable("~/Desktop/waveshaper_chebyshev_3rd_256_int8.h", "CHEBYSHEV_3RD_256", 256, 3)
        chebyTable("~/Desktop/waveshaper_chebyshev_4th_256_int8.h", "CHEBYSHEV_4TH_256", 256, 4)
        chebyTable("~/Desktop/waveshaper_chebyshev_5th_256_int8.h", "CHEBYSHEV_5TH_256", 256, 5)
        chebyTable("~/Desktop/waveshaper_chebyshev_6th_256_int8.h", "CHEBYSHEV_6TH_256", 256, 6)
        
    Resources:
        http://www.obiwannabe.co.uk/html/music/6SS/six-waveshaper.html
        http://mathworld.wolfram.com/ChebyshevPolynomialoftheFirstKind.html
        The first few Chebyshev polynomials of the first kind are
        T_0(x)  =   1
        T_1(x)  =   x
        T_2(x)  =   2x^2-1
        T_3(x)  =   4x^3-3x
        T_4(x)  =   8x^4-8x^2+1
        T_5(x)  =   16x^5-20x^3+5x
        T_6(x)  =   32x^6-48x^4+18x^2-1
        
    """
    
    fout = open(os.path.expanduser(outfile), "w")
    fout.write('#ifndef ' + tablename + '_H_' + '\n')
    fout.write('#define ' + tablename + '_H_' + '\n \n')
    fout.write('#if ARDUINO >= 100'+'\n')
    fout.write('#include "Arduino.h"'+'\n')
    fout.write('#else'+'\n')
    fout.write('#include "WProgram.h"'+'\n')
    fout.write('#endif'+'\n')   
    fout.write('#include "mozzi_pgmspace.h"'+'\n \n')
    fout.write('#define ' + tablename + '_NUM_CELLS '+ str(tablelength) +'\n')
    outstring = 'CONSTTABLE_STORAGE(int8_t) ' + tablename + '_DATA [] = {'
    try:
        for num in range(tablelength):
            
            x = 2*(float(num-(tablelength/2)))/tablelength

            if curvenum == 3:
                t_x = 4*pow(x,3)-3*x
            elif curvenum == 4:
                t_x = 8*pow(x,4)-8*pow(x,2)+1
            elif curvenum == 5:
                t_x = 16*pow(x,5)-20*pow(x,3)+5*x
            elif curvenum == 6:
                t_x = 32*pow(x,6)-48*pow(x,4)+18*pow(x,2)-1

            scaled = int16_t(math.floor(t_x*127.999))

            outstring += str(scaled) + ", "
    finally:
        outstring +=  "};"
        outstring = textwrap.fill(outstring, 80)
        fout.write(outstring)
        fout.write('\n \n #endif /* ' + tablename + '_H_ */\n')
        fout.close()
        print "wrote " + outfile