| public codeSymbol ( int bit, int context ) : void | ||
| bit | int | The symbol to be encoded, must be 0 or 1. /// /// |
| context | int | the context with which to encode the symbol. /// /// |
| return | void | |
public void codeSymbol(int bit, int context)
{
int q;
int li; // local cache of I[context]
int la;
int n;
// NOTE: (a < 0x8000) is equivalent to ((a & 0x8000)==0)
// since 'a' is always less than or equal to 0xFFFF
// NOTE: conditional exchange guarantees that A for MPS is
// always greater than 0x4000 (i.e. 0.375)
// => one renormalization shift is enough for MPS
// => no need to do a renormalization while loop for MPS
li = I[context];
q = qe[li]; // Retrieve current LPS prob.
if (bit == mPS[context])
{
// -- Code MPS
a -= q; // Interval division associated with MPS coding
if (a >= 0x8000)
{
// Interval big enough
c += q;
}
else
{
// Interval too short
if (a < q)
{
// Probabilities are inverted
a = q;
}
else
{
c += q;
}
I[context] = nMPS[li];
// -- Renormalization (MPS: no need for while loop)
a <<= 1; // a is doubled
c <<= 1; // c is doubled
cT--;
if (cT == 0)
{
byteOut();
}
// -- End of renormalization
}
}
else
{
// -- Code LPS
la = a; // cache A register in local variable
la -= q; // Interval division according to LPS coding
if (la < q)
{
c += q;
}
else
{
la = q;
}
if (switchLM[li] != 0)
{
mPS[context] = 1 - mPS[context];
}
I[context] = nLPS[li];
// -- Renormalization
// sligthly better than normal loop
n = 0;
do
{
la <<= 1;
n++; // count number of necessary shifts
}
while (la < 0x8000);
if (cT > n)
{
c <<= n;
cT -= n;
}
else
{
do
{
c <<= cT;
n -= cT;
// cT = 0; // not necessary
byteOut();
}
while (cT <= n);
c <<= n;
cT -= n;
}
// -- End of renormalization
a = la; // save cached A register
}
}