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// from .cpp file in original kernel
//#define length 512

#if mykernel == 1

/**
 * One instance of this kernel call is a thread.
 * Each thread finds out the segment in which it should look for the element.
 * After that, it checks if the element is between the lower bound and upper bound
 * of its segment. If yes, then this segment becomes the total searchspace for the next pass.
 *
 * To achieve this, it writes the lower bound and upper bound to the output array.
 * In case the element at the left end (lower bound) matches the element we are looking for,
 * That is marked in the output and we no longer need to look any further.
 */
__kernel void
binarySearch(        __global uint4 * outputArray,
             __const __global uint  * sortedArray, 
             const   unsigned int findMe,
             const   unsigned int globalLowerBound, 
             const   unsigned int globalUpperBound, 
             const   unsigned int subdivSize)
{
    __requires(subdivSize == 1024);
    __requires(globalLowerBound == 0);
    
    unsigned int tid = get_global_id(0);

    /* lower bound and upper bound are computed from segment and total search space for this pass
     * The total search space is known from global lower and upper bounds for this pass.
     */
    unsigned int lowerBound = globalLowerBound + subdivSize * tid;
    unsigned int upperBound = lowerBound + subdivSize - 1;

#ifndef ORIGINAL
    // Encode assumption that the array is strictly sorted
#define ORDERING(x, y, A) __implies((x) < (y), A[x] < A[y])    
    __assume(ORDERING(lowerBound, upperBound, sortedArray));
    __assume(ORDERING(__other_int(upperBound), lowerBound, sortedArray));
    __assume(ORDERING(upperBound, __other_int(lowerBound), sortedArray));

#endif
    
    /* Then we find the elements at the two ends of the search space for this thread */
    unsigned int lowerBoundElement = sortedArray[lowerBound];
    unsigned int upperBoundElement = sortedArray[upperBound];

    /* If the element to be found does not lie between them, then nothing left to do in this thread */
    if( (lowerBoundElement > findMe) || (upperBoundElement < findMe))
    {
        return;
    }
    else
    {
        /* However, if the element does lie between the lower and upper bounds of this thread's searchspace
         * we need to narrow down the search further in this search space 
         */
 
        /* The search space for this thread is marked in the output as being the total search space for the next pass */
        outputArray[0].x = lowerBound;
        outputArray[0].y = upperBound;
        outputArray[0].w = 1;

    }
}
#endif


#if mykernel == 2

__kernel void
binarySearch_mulkeys(__global int *keys,
                    __global uint *input,
                    const unsigned int numKeys,
                    __global int *output)
{
    __requires(numKeys < (1 << 24));
    
    int gid = get_global_id(0);
    int lBound = gid * 256;
    int uBound = lBound + 255;

#ifndef ORIGINAL
    // Encode assumption that the array is strictly sorted
#define ORDERING(x, y, A) __implies((x) < (y), A[x] < A[y])    
    __assume(ORDERING(lBound, uBound, input));
    __assume(ORDERING(__other_int(uBound), lBound, input));
    __assume(ORDERING(uBound, __other_int(lBound), input));

#endif

    for(int i = 0;
        __invariant(__write_implies(output, (__write_offset_bytes(output)/sizeof(int)) < i)),
        i < numKeys; i++)
    {
        if(keys[i] >= input[lBound] && keys[i] <=input[uBound])
            output[i]=lBound;
    }
    
}

#endif

#if mykernel == 3

__kernel void
binarySearch_mulkeysConcurrent(__global uint *keys,
                    __global uint *input,
                    const unsigned int inputSize, // number of input elements
                    const unsigned int numSubdivisions,
                    __global int *output)
{
    int lBound = (get_global_id(0) % numSubdivisions) * (inputSize / numSubdivisions);
    int uBound = lBound + inputSize / numSubdivisions;
    int myKey = keys[get_global_id(0) / numSubdivisions];
    int mid;
    while(uBound >= lBound)
    {
        mid = (lBound + uBound) / 2;
        if(input[mid] == myKey)
        {
            output[get_global_id(0) / numSubdivisions] = mid;
            return;
        }
        else if(input[mid] > myKey)
            uBound = mid - 1;
        else
            lBound = mid + 1;
    }
}

#endif

