/usr/include/tesseract/qrsequence.h is in libtesseract-dev 3.02.01-6.
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// File: qrsequence.h
// Description: Quasi-random sequence generator class.
// Author: Ranjith Unnikrishnan
// Created: Wed May 20 2009
//
// Class to generate a (deterministic) quasi-random Van der Corput sequence that
// covers the interval [0,N) without repetition.
//
// The sequence is generated by reversing the base-2 representation of the
// sequence of natural numbers {0, 1,... M-1}, where M is 2^{num_bits_} and
// num_bits is the minimum number of bits required to represent N. If a reversed
// numbers is >= N it is rejected and the next natural number is considered
// until a valid output number is found.
//
// (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.
//
///////////////////////////////////////////////////////////////////////
#ifndef TESSERACT_CCUTIL_QRSEQUENCE_H_
#define TESSERACT_CCUTIL_QRSEQUENCE_H_
#include <math.h>
class QRSequenceGenerator {
public:
// Object is initalized with the size of the output range.
explicit QRSequenceGenerator(int N) : N_(N), next_num_(0) {
num_bits_ = static_cast<int>(ceil(log(static_cast<double>(N)) / log(2.0)));
}
// Main worker method that retrieves the next number in the sequence.
// Returns kInvalidVal if called more than N times after object initialization
int GetVal() {
const int kInvalidVal = -1;
const int kMaxNaturalNumberValue = 1 << num_bits_;
if (next_num_ >= kMaxNaturalNumberValue)
return kInvalidVal;
int n = next_num_;
while (next_num_ < kMaxNaturalNumberValue) {
n = GetBinaryReversedInteger(next_num_++);
if (n < N_) break;
}
return (next_num_ > kMaxNaturalNumberValue) ? kInvalidVal : n;
}
protected:
// Outputs the integer formed by reversing the bits of the input integer. Only
// the lowest num_bits_ bits of the input integer are reversed.
int GetBinaryReversedInteger(int in_val) const {
int bit_pos = num_bits_;
int out_val = 0;
while(bit_pos--) {
// Set the value of the last bit.
out_val |= (in_val & 0x1);
if (bit_pos > 0) {
// Left-shift output value to prepare for storing the next bit.
out_val <<= 1;
}
// Right-shift input value to prepare for retrieving the next bit.
in_val >>= 1;
}
return out_val;
}
int N_;
// Next number to be considered for reversal and output.
int next_num_;
// number of bits required to represent the numbers of the sequence
int num_bits_;
};
#endif // TESSERACT_CCUTIL_QRSEQUENCE_H_
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