dcmjpls/libcharls/context.h

//
// (C) Jan de Vaan 2007-2010, all rights reserved. See the accompanying "License.txt" for licensed use.
//


#ifndef CHARLS_CONTEXT
#define CHARLS_CONTEXT


//
// JlsContext: a JPEG-LS context with it's current statistics.
//
struct JlsContext
{
public:
    JlsContext()
    {}

    JlsContext(LONG a) :
        A(a),
        B(0),
        C(0),
        N(1)
    {
    }

    LONG A;
    LONG B;
    short C;
    short N;

    inlinehint LONG GetErrorCorrection(LONG k) const
    {
        if (k != 0)
            return 0;

        return BitWiseSign(2 * B + N - 1);
    }


    inlinehint void UpdateVariables(LONG errorValue, LONG NEAR, LONG NRESET)
    {
        ASSERT(N != 0);

        // For performance work on copies of A,B,N (compiler will use registers).
        int b = B + errorValue * (2 * NEAR + 1);
        int a = A + ABS(errorValue);
        int n = N;

        ASSERT(a < 65536 * 256);
        ASSERT(ABS(b) < 65536 * 256);

        if (n == NRESET)
        {
            a = a >> 1;
            b = b >> 1;
            n = n >> 1;
        }

        n = n + 1;

        if (b + n <= 0)
        {
            b = b + n;
            if (b <= -n)
            {
                b = -n + 1;
            }
            C = _tableC[C - 1];
        }
        else  if (b > 0)
        {
            b = b - n;
            if (b > 0)
            {
                b = 0;
            }
            C = _tableC[C + 1];
        }
        A = a;
        B = b;
        N = (short)n;
        ASSERT(N != 0);
    }



    inlinehint LONG GetGolomb() const
    {
        LONG Ntest  = N;
        LONG Atest  = A;
        LONG k = 0;
        for(; (Ntest << k) < Atest; k++)
        {
            ASSERT(k <= 32);
        };
        return k;
    }

    static signed char* CreateTableC()
    {
        static OFVector<signed char> rgtableC;

        rgtableC.reserve(256 + 2);

        rgtableC.push_back(-128);
        for (int i = -128; i < 128; i++)
        {
            rgtableC.push_back(char(i));
        }
        rgtableC.push_back(127);

        signed char* pZero = &rgtableC[128 + 1];
        ASSERT(pZero[0] == 0);
        return pZero;
    }
private:

    static signed char* _tableC;
};

#endif

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