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@(@\newcommand{\W}[1]{ \; #1 \; } \newcommand{\R}[1]{ {\rm #1} } \newcommand{\B}[1]{ {\bf #1} } \newcommand{\D}[2]{ \frac{\partial #1}{\partial #2} } \newcommand{\DD}[3]{ \frac{\partial^2 #1}{\partial #2 \partial #3} } \newcommand{\Dpow}[2]{ \frac{\partial^{#1}}{\partial {#2}^{#1}} } \newcommand{\dpow}[2]{ \frac{ {\rm d}^{#1}}{{\rm d}\, {#2}^{#1}} }@)@
Set Up Multi-threading Sum of 1/i

Syntax
ok = harmonic_setup(num_sum)
Purpose
This routine does the setup for splitting the summation that defines the harmonic series @[@ 1 + 1/2 + 1/3 + ... + 1/n @]@ into separate parts for each thread.

Thread
It is assumed that this function is called by thread zero, and all the other threads are blocked (waiting).

num_sum
The argument num_sum has prototype
     size_t num_sum
 It specifies the value of @(@ n @)@ in the summation.

Source 

namespace {
bool harmonic_setup(size_t num_sum)
{     // sum = 1/num_sum + 1/(num_sum-1) + ... + 1
     size_t num_threads  = std::max(num_threads_, size_t(1));
     bool ok             = num_threads == thread_alloc::num_threads();
     ok                 &= thread_alloc::thread_num() == 0;
     ok                 &= num_sum >= num_threads;
     //
     for(size_t thread_num = 0; thread_num < num_threads; thread_num++)
     {     // allocate separate memory for this thread to avoid false sharing
          size_t min_bytes(sizeof(work_one_t)), cap_bytes;
          void* v_ptr = thread_alloc::get_memory(min_bytes, cap_bytes);
          work_all_[thread_num] = static_cast<work_one_t*>(v_ptr);
          //
          // in case this thread's worker does not get called
          work_all_[thread_num]->ok = false;
          // parameters that define the work for this and previous thread
          if( thread_num == 0 )
               work_all_[0]->start = 1;
          else
          {     size_t index  = (num_sum * thread_num) / num_threads;
               work_all_[thread_num-1]->stop = index;
               work_all_[thread_num]->start  = index;
          }
     }
     work_all_[num_threads-1]->stop = num_sum + 1;
     return ok;
}
}
Input File: example/multi_thread/harmonic.cpp