shader/common.glsl


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// GLSL Arbitrary Precision (modified a little bit)
// https://github.com/alexozer/glsl-arb-prec

// Number of Integers used to store an Arbitrary-Precision Number
//const int n_int = 3;
#define n_int 3

// Power of 10 one larger than the maximum value per int
//const int limit = 10000;
#define limit 32768

const float limitFlt = float(limit);

int result[n_int];

#define zero(x, len) for(int i=0;i<len;i++){x[i]=0;}
#define assign(x, y) for(int i=0;i<n_int;i++){x[i]=y[i];}
#define negate(x) for(int i=0;i<n_int;i++){x[i]=-x[i];}

bool signp(int[n_int] a)
{
    return a[n_int-1] >= 0;
}

int keepVal, carry;

void roundOff(int x)
{
    carry = x/limit;
    keepVal = x-carry*limit;
}

void add(int[n_int] a, int[n_int] b) {
    bool s1 = signp(a), s2 = signp(b);

    carry = 0;

    for(int i = 0; i < n_int-1; i++) {
        roundOff(a[i] + b[i] + carry);

        if(keepVal < 0) {
            keepVal += limit;
            carry--;
        }

        result[i] = keepVal;
    }
    roundOff(a[n_int-1] + b[n_int-1] + carry);
    result[n_int-1] = keepVal;
    
    if(s1 != s2 && !signp(result)) {
        negate(result);

        carry = 0;

        for(int i = 0; i < n_int; i++) {
            roundOff(result[i] + carry);

            if(keepVal < 0) {
                keepVal += limit;
                carry--;
            }

            result[i] = keepVal;
        }

        negate(result);
    }
}

void mul(int[n_int] a, int[n_int] b) {
    bool toNegate = false;

    if(!signp(a)) {
        negate(a);
        toNegate = !toNegate;
    }
    if(!signp(b)) {
        negate(b);
        toNegate = !toNegate;
    }

    const int lenProd = (n_int-1)*2+1;
    int prod[lenProd];
    zero(prod, lenProd);

    for(int i = 0; i < n_int; i++) {
        for(int j = 0; j < n_int; j++) {
            prod[i+j] += a[i] * b[j];
        }
    }

    carry = 0;
    const int clip = lenProd - n_int;
    for(int i = 0; i < clip; i++) {
        roundOff(prod[i] + carry);
        prod[i] = keepVal;
    }

    if(prod[clip-1] >= limit/2) {
        carry++;
    }

    for(int i = clip; i < lenProd; i++) {
        roundOff(prod[i] + carry);
        prod[i] = keepVal;
    }

    for(int i = 0; i < lenProd - clip; i++) {
        result[i] = prod[i+clip];
    }

    if(toNegate) {
        negate(result);
    }
}

int[n_int] loadFloat(float f)
{
    int x[n_int];

    for(int i = n_int-1; i >= 0; i--)
    {
        int fCurr = int(f);
        x[i] = fCurr;
        f -= float(fCurr);
        f *= limitFlt;
    }

    return x;
}