tesseract/src/ccstruct/dppoint.cpp
Stefan Weil dabf3c299f Fix file endings
Text files should end with a LF, but not additional empty lines.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
2018-04-25 19:35:33 +02:00

98 lines
3.6 KiB
C++

/**********************************************************************
* File: dppoint.cpp
* Description: Simple generic dynamic programming class.
* Author: Ray Smith
* Created: Wed Mar 25 19:08:01 PDT 2009
*
* (C) Copyright 2009, Google Inc.
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
** http://www.apache.org/licenses/LICENSE-2.0
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*
**********************************************************************/
#include "dppoint.h"
#include "tprintf.h"
namespace tesseract {
// Solve the dynamic programming problem for the given array of points, with
// the given size and cost function.
// Steps backwards are limited to being between min_step and max_step
// inclusive.
// The return value is the tail of the best path.
DPPoint* DPPoint::Solve(int min_step, int max_step, bool debug,
CostFunc cost_func, int size, DPPoint* points) {
if (size <= 0 || max_step < min_step || min_step >= size)
return nullptr; // Degenerate, but not necessarily an error.
ASSERT_HOST(min_step > 0); // Infinite loop possible if this is not true.
if (debug)
tprintf("min = %d, max=%d\n",
min_step, max_step);
// Evaluate the total cost at each point.
for (int i = 0; i < size; ++i) {
for (int offset = min_step; offset <= max_step; ++offset) {
DPPoint* prev = offset <= i ? points + i - offset : nullptr;
int64_t new_cost = (points[i].*cost_func)(prev);
if (points[i].best_prev_ != nullptr && offset > min_step * 2 &&
new_cost > points[i].total_cost_)
break; // Find only the first minimum if going over twice the min.
}
points[i].total_cost_ += points[i].local_cost_;
if (debug) {
tprintf("At point %d, local cost=%d, total_cost=%d, steps=%d\n",
i, points[i].local_cost_, points[i].total_cost_,
points[i].total_steps_);
}
}
// Now find the end of the best path and return it.
int best_cost = points[size - 1].total_cost_;
int best_end = size - 1;
for (int end = best_end - 1; end >= size - min_step; --end) {
int cost = points[end].total_cost_;
if (cost < best_cost) {
best_cost = cost;
best_end = end;
}
}
return points + best_end;
}
// A CostFunc that takes the variance of step into account in the cost.
int64_t DPPoint::CostWithVariance(const DPPoint* prev) {
if (prev == nullptr || prev == this) {
UpdateIfBetter(0, 1, nullptr, 0, 0, 0);
return 0;
}
int delta = this - prev;
int32_t n = prev->n_ + 1;
int32_t sig_x = prev->sig_x_ + delta;
int64_t sig_xsq = prev->sig_xsq_ + delta * delta;
int64_t cost = (sig_xsq - sig_x * sig_x / n) / n;
cost += prev->total_cost_;
UpdateIfBetter(cost, prev->total_steps_ + 1, prev, n, sig_x, sig_xsq);
return cost;
}
// Update the other members if the cost is lower.
void DPPoint::UpdateIfBetter(int64_t cost, int32_t steps, const DPPoint* prev,
int32_t n, int32_t sig_x, int64_t sig_xsq) {
if (cost < total_cost_) {
total_cost_ = cost;
total_steps_ = steps;
best_prev_ = prev;
n_ = n;
sig_x_ = sig_x;
sig_xsq_ = sig_xsq;
}
}
} // namespace tesseract.