Hw3 #424
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Hw3 #424
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| //for (j = 1; j <= lim; j++) { // YOUR CODE HERE | ||
| offset=get_local_size(0)>>j; | ||
| //printf("global_id[%d], offset=%d\n",global_id,offset); | ||
| fast[local_id]=fast[local_id]+fast[local_id+offset]; |
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If you compare this to the code in the link above, you'll see that an if statement is missing.
This causes 2 issues:
- Some threads may access data that is beyond the end of the input array.
- The output may differ because in some iteration, given two threads A and B (where B_id = A_id + offset), B may update its value, and then A will read the new value.
This may also explain why you saw an error when using more than 32 threads, or when the global size was larger than 4096.
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