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<div style="color: rgb(0, 0, 0);">The following code is in filetype.c, function `NC_start_count_stride_ck`</div>
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<div style="color: rgb(0, 0, 0);"> for (; i<varp->ndims; i++) {</div>
<div> if (start[i] < 0 ||<font color="#ff0000"> start[i] >= varp->shape[i]</font>)</div>
<div style="color: rgb(0, 0, 0);"> DEBUG_RETURN_ERROR(NC_EINVALCOORDS)</div>
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<div style="color: rgb(0, 0, 0);"> if (varp->shape[i] < 0) DEBUG_RETURN_ERROR(NC_EEDGE)</div>
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<div style="color: rgb(0, 0, 0);"> if (count != NULL) {</div>
<div style="color: rgb(0, 0, 0);"> if (count[i] < 0) /* no negative count[] */</div>
<div style="color: rgb(0, 0, 0);"> DEBUG_RETURN_ERROR(NC_ENEGATIVECNT)</div>
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<div style="color: rgb(0, 0, 0);"> if (stride == NULL) { /* for vara APIs */</div>
<div style="color: rgb(0, 0, 0);"> if (count[i] > varp->shape[i] ||</div>
<div style="color: rgb(0, 0, 0);"> start[i] + count[i] > varp->shape[i])</div>
<div style="color: rgb(0, 0, 0);"> DEBUG_RETURN_ERROR(NC_EEDGE)</div>
<div style="color: rgb(0, 0, 0);"> }</div>
<div style="color: rgb(0, 0, 0);"> else { /* for vars APIs */</div>
<div style="color: rgb(0, 0, 0);"> if (count[i] > 0 &&</div>
<div style="color: rgb(0, 0, 0);"> start[i] + (count[i]-1) * stride[i] >= varp->shape[i])</div>
<div style="color: rgb(0, 0, 0);"> DEBUG_RETURN_ERROR(NC_EEDGE)</div>
<div style="color: rgb(0, 0, 0);"> if (stride[i] == 0) DEBUG_RETURN_ERROR(NC_ESTRIDE)</div>
<div style="color: rgb(0, 0, 0);"> }</div>
<div style="color: rgb(0, 0, 0);"> }</div>
<div style="color: rgb(0, 0, 0);"> /* else is for var1 APIs */</div>
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<div style="color: rgb(0, 0, 0);">There is an issue when the process with the highest rank has zero items to output. As an example, if I have 4 mpi processes which are each writing the following amount of data:</div>
<div style="color: rgb(0, 0, 0);"> * rank 0: 0 items</div>
<div style="color: rgb(0, 0, 0);"> * rank 1: 2548 items</div>
<div style="color: rgb(0, 0, 0);"> * rank 2: 4352 items</div>
<div style="color: rgb(0, 0, 0);"> * rank 3: 0 items.</div>
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<div style="color: rgb(0, 0, 0);">I will define the variable to have a length of 6900 items (0 + 2548 + 4352 + 0). When I am outputting data to the variable, each rank will call nc_put_vara_longlong with the following start and count values:</div>
<div style="color: rgb(0, 0, 0);"> * rank 0: start = 0, count = 0</div>
<div style="color: rgb(0, 0, 0);"> * rank 1: start = 0, count = 2548</div>
<div style="color: rgb(0, 0, 0);"> * rank 2: start = 2548, count = 4352</div>
<div style="color: rgb(0, 0, 0);"> * rank 3: start = 6900, count = 0.</div>
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<div style="color: rgb(0, 0, 0);">In each case, the `start` for rank N is equal to `start` for rank N-1 + `count` for rank N-1. This all works ok until the highest rank is writing 0 items. In that case, the `start` value for that rank is equal to the total
size of the variable and the check in the code fragment shown above fails since `start[i] == varp->shape[i]`.</div>
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<div style="color: rgb(0, 0, 0);">This could be fixed in the application code by checking whether the `count` is zero and if so, then set `start` to 0 also, but I think that is a kluge that should not be required. </div>
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<div style="color: rgb(0, 0, 0);">My suggestion is to make the test be:</div>
<div style="color: rgb(0, 0, 0);">```</div>
<div> if (start[i] < 0 || (start[i] >= varp->shape[i] <font color="#ff0000">&& count[i] > 0</font><span style="color: rgb(0, 0, 0);">))</span></div>
<div style="color: rgb(0, 0, 0);">```</div>
<div style="color: rgb(0, 0, 0);">This is in version 1.7.0. It also appears in 1.6.1 in the function Nccoordck.</div>
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<div style="color: rgb(0, 0, 0);">..Greg</div>
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<div id="MAC_OUTLOOK_SIGNATURE">
<div>-- </div>
<div>"A supercomputer is a device for turning compute-bound problems into I/O-bound problems”</div>
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