Function mem_getTotalGlobalMemoryUsed

quest/src/core/memory.cpp:248–281

qindex mem_getTotalGlobalMemoryUsed(Qureg qureg) {

    /// @todo
    ///  if sizeof(qcomp) is a power of 2 (which it almost always is, c'mon now),
    ///  then we could instead return the LOG of the total memory and always
    ///  avoid overflow, permitting reporters to display mem=2^exp.
    ///  it would also make changing units (e.g. to GB) easier.

    // work out individual array costs
    qindex memLocalArray = (qindex) mem_getLocalQuregMemoryRequired(qureg.numAmpsPerNode); // never overflows
    int numLocalArrays = 
        mem_isAllocated(qureg.cpuAmps) + mem_isAllocated(qureg.cpuCommBuffer) +
        mem_isAllocated(qureg.gpuAmps) + mem_isAllocated(qureg.gpuCommBuffer);  // but 4*memLocalArray might overflow

    // if total local costs would overflow qindex, return 0
    qindex maxQindex = std::numeric_limits<qindex>::max();
    qindex maxLocalArrayMem = maxQindex / numLocalArrays; // floors
    if (memLocalArray > maxLocalArrayMem)
        return 0;

    // if qureg is non-distributed, compute local CPU+GPU+buffers costs and return
    qindex memLocalTotal = numLocalArrays * memLocalArray;
    if (!qureg.isDistributed)
        return memLocalTotal;

    // else if total global costs would overflow qindex, return 0
    qindex maxLocalTotalMem = maxQindex / qureg.numNodes; // floors
    if (memLocalTotal > maxLocalTotalMem)
        return 0;

    // else compute total costs between all nodes
    qindex memGlobalTotal = memLocalTotal * qureg.numNodes;
    return memGlobalTotal;
}