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/*
* ReorderingStack.cpp
** Author: Ankit K. Srivastava
** Date: Jan 26, 2010
*/
#include <vector>
#include "ReorderingStack.h"
#include "../../MemPool.h"
namespace Moses2
{
ReorderingStack::ReorderingStack(MemPool &pool) :
m_stack(pool)
{
}
void ReorderingStack::Init()
{
m_stack.clear();
}
size_t ReorderingStack::hash() const
{
std::size_t ret = boost::hash_range(m_stack.begin(), m_stack.end());
return ret;
}
bool ReorderingStack::operator==(const ReorderingStack& o) const
{
const ReorderingStack& other = static_cast<const ReorderingStack&>(o);
return m_stack == other.m_stack;
}
// Method to push (shift element into the stack and reduce if reqd)
int ReorderingStack::ShiftReduce(const Range &input_span)
{
int distance; // value to return: the initial distance between this and previous span
// stack is empty
if (m_stack.empty()) {
m_stack.push_back(input_span);
return input_span.GetStartPos() + 1; // - (-1)
}
// stack is non-empty
Range prev_span = m_stack.back(); //access last element added
//calculate the distance we are returning
if (input_span.GetStartPos() > prev_span.GetStartPos()) {
distance = input_span.GetStartPos() - prev_span.GetEndPos();
}
else {
distance = input_span.GetEndPos() - prev_span.GetStartPos();
}
if (distance == 1) { //monotone
m_stack.pop_back();
Range new_span(prev_span.GetStartPos(), input_span.GetEndPos());
Reduce(new_span);
}
else if (distance == -1) { //swap
m_stack.pop_back();
Range new_span(input_span.GetStartPos(), prev_span.GetEndPos());
Reduce(new_span);
}
else { // discontinuous
m_stack.push_back(input_span);
}
return distance;
}
// Method to reduce, if possible the spans
void ReorderingStack::Reduce(Range current)
{
bool cont_loop = true;
while (cont_loop && m_stack.size() > 0) {
Range previous = m_stack.back();
if (current.GetStartPos() - previous.GetEndPos() == 1) { //mono&merge
m_stack.pop_back();
Range t(previous.GetStartPos(), current.GetEndPos());
current = t;
}
else if (previous.GetStartPos() - current.GetEndPos() == 1) { //swap&merge
m_stack.pop_back();
Range t(current.GetStartPos(), previous.GetEndPos());
current = t;
}
else { // discontinuous, no more merging
cont_loop = false;
}
} // finished reducing, exit
// add to stack
m_stack.push_back(current);
}
}
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