OPL2 PG

global lu_exp;
global lu_log;
function initLookups()
    disp("Initializing lookup tables");
    global lu_exp;
    lu_exp = zeros(1,256,"int32");
    global lu_log;
    lu_log = zeros(1,256,"int32");
    for i=0:255
        lu_log(i+1) = round(-log2( sin((double(i)+0.5)*pi/2/256) )*256);
        lu_exp(i+1) = round((power(2, double(i)/256)-1)*1024);
    endfor
endfunction
initLookups();

function y=eMap(x)
    eff = bitand(x,255);
    if(bitand(x, 256) == 0)
        y = eff;
    else
        y = bitxor(eff, 255);
    endif
endfunction
function y=eExp(val)
    global lu_exp;
    y = lu_exp(bitand(val,255)+1);
    # now reverse calculate the floating point value...
    y = bitshift(1024+y, bitshift(val,-8));
endfunction
function y=eLog(phase)
    global lu_log;
    y = lu_log(eMap(phase)+1);
endfunction
function y=eSin(amp, phase)
    phase = bitand(phase, 1023);
    amp = bitshift(amp-64, 4);
    y = eExp(amp-eLog(phase));
    if(bitand(phase,512)!=0)
        y = -y;
    endif
endfunction
function y=eSinV(amp,phase,vamp,vphase)
    y = eSin(amp, phase+eSin(vamp,vphase));
endfunction

function y = sintest(phase)
    #y = eSinV(63, phase, 16, phase/3);
    y = eSin(0, phase);
endfunction

x = 0:1023;
sl = arrayfun(@eLog, x);
se = arrayfun(@eExp, x);
st = arrayfun(@sintest, x);
plot(x, st, ";Sin;");
#plot(x, sl, ";Logarithmic lookup;", x, se, ";Exponential lookup;", x, st, ";Calculated sine wave;");#, x, abs(((st.-16384*sin(x./1024*pi*2)).*10000./st)), "--;Rel. error to real sine (x10000);");
title("OPL2 Sine wave");
xlabel("Phase (0-1023)");
ylabel("Value (Amplitude = 256)");
grid;