source: CIVL/examples/cuda/pathfinder.cvl@ 63812cc

/**
 * This file is modified from the original pathfinder_cuda.cvl 
 * program by the following way:
 * First, GPU/GPU_BLOCK/GPU_THREAD no longer access global variables of 
 * int type, but use their value (by parameter passing) instead.
 */

#include<civlc.h>

//pyramid height of 0 does nothing, of 1 is normal stencil, 2 is where
//the algorithm even kicks in
#define pyramid_height 2

//This is how many iterations of the loop (minus 1). If less than
//the pyramid_height, then the pyramid_height does nothing.
#define rows 3

//I think this is the minimum this can be to be useful
//(the number of cells)
#define cols 2


//BLOCK_SIZE must satisfy (BLOCK_SIZE > pyramid_height*2)
#define BLOCK_SIZE 5
#define HALO 1

int borderCols     = (pyramid_height)*HALO;
int smallBlockCol  = BLOCK_SIZE - (pyramid_height) * HALO * 2;
int blockCols      = cols/smallBlockCol+((cols%smallBlockCol==0)?0:1);

int result[cols];

//GPU MEMORY (couldn't do it scoped because need references to memory
//on host side)
int gpuResult[2][cols];
int gpuWall[rows*cols - cols];

//$input int wall[rows][cols];

#define IN_RANGE(x, min, max)   ((x)>=(min) && (x)<=(max))
#define CLAMP_RANGE(x, min, max) x = (x<(min)) ? min : ((x>(max)) ? max : x )
#define MIN(a, b) ((a)<=(b) ? (a) : (b))

//Not implemented yet.
//void __syncthreads() {
//}

void GPU_THREAD(int tx, int tbx, int tIteration, int tBorderCols, int src, int dst, int* prev, int* result, int startStep){ 
    int small_block_cols = BLOCK_SIZE-tIteration*HALO*2;
    int blkX = small_block_cols*tbx-tBorderCols;
    int blkXmax = blkX+BLOCK_SIZE-1;
    
    // calculate the global thread coordination
    int xidx = blkX+tx;
    
    // effective range within this block that falls within
    // the valid range of the input data
    // used to rule out computation outside the boundary.
    int validXmin = (blkX < 0) ? -blkX : 0;
    int validXmax = (blkXmax > cols-1) ? BLOCK_SIZE-1-(blkXmax-cols+1) : BLOCK_SIZE-1;
    
    int W = tx-1;
    int E = tx+1;
    
    W = (W < validXmin) ? validXmin : W;
    E = (E > validXmax) ? validXmax : E;

    int isValid = IN_RANGE(tx, validXmin, validXmax);    
    if(IN_RANGE(xidx, 0, cols-1)){
        prev[tx] = gpuResult[src][xidx];
    }

    int computed;
    
    for (int i=0; i<tIteration; i++){
        computed = 0;
        if( IN_RANGE(tx, i+1, BLOCK_SIZE-i-2) && isValid) {
                computed = 1;
                int left = prev[W];
                int up = prev[tx];
                int right = prev[E];
                int shortest = MIN(left, up);
                shortest = MIN(shortest, right);
                int index = cols*(startStep+i)+xidx;
                result[tx] = shortest + gpuWall[index];
        }
        
        //Break not implemented yet...
        /* if(i==iteration-1)  */
        /*   break;  */
        if(computed != 0)        //Assign the computation range
                prev[tx]= result[tx];
        //__syncthreads();         // [Ronny] Added sync to avoid race on prev Aug. 14 201
    }
    
    // update the global memory
    // after the last iteration, only threads coordinated within the
    // small block perform the calculation and switch on ``computed''
    if (computed != 0) {
        gpuResult[dst][xidx]=result[tx];
    }
}

void GPU_BLOCK(int bx, int bIteration, int bBorderCols, int src, int dst, int startStep){
    //shared memory
    int prev[BLOCK_SIZE];
    int result[BLOCK_SIZE];
    $proc thread_procs[BLOCK_SIZE];
  
    //Launch the threads per block
    for (int tp = 0; tp < BLOCK_SIZE; tp++) {
      thread_procs[tp] = $spawn GPU_THREAD(tp, bx, bIteration, bBorderCols, src, dst, prev, result, startStep);
    }
    
    for (int tp = 0; tp < BLOCK_SIZE; tp++) {
      $wait thread_procs[tp];
    }
}

void GPU(int iteration, int src, int dst, int startStep, int blocks, int threads, int gBorderCols) {
        $proc block_procs[blocks];
        
        //Launch the blocks
        for (int b = 0; b < blocks; b++) {
                block_procs[b] = $spawn GPU_BLOCK(b, iteration, gBorderCols, src,  dst, startStep);
        }
        
        for (int b = 0; b < blocks; b++) {
                $wait block_procs[b];
        }    
}

void calc_path() {
        int src = 1, dst = 0;
        for (int t = 0; t < rows-1; t+=pyramid_height) {
                int temp = src;
                src = dst;
                dst = temp;
                GPU(MIN(pyramid_height, rows-t-1), src, dst,t, blockCols, BLOCK_SIZE, borderCols);
        }    
}

void main() {
        $assert BLOCK_SIZE > pyramid_height*2;
        calc_path();
        $assert 1 == 1;
}