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delta_trans Class Template Reference

The delta transform. More...

#include <delta.h>

List of all members.

Public Methods
void	forward (T *vec, size_t len)
	Convert the value in the array into an initial reference value and a set of delta values. More...
void	inverse (T *vec, size_t len)

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Detailed Description

template<class T> class delta_trans

The delta transform.

A data set of N elements is replaced by the differences. In this simple algorithm

  si = si - si-1.
  

For an array indexed from 0, i = 1 to N-1. The element at s₀ is the reference element, which is unchanged. The next element at s₁ is replaced by the difference between that element and s₀.

The algorithm implemented here is an in-place algorithm which replaces the original data in the forward transform and reconstructs the data from in-place in the inverse transform.

The class is implemented as a template class. Obviously the type used to instantiate the template must support signed arithmetic.

The class was written as a comparision baseline for the wavelet compresson algorithms. The "delta" algorithm is very simple and has a time complexity of N, where as the wavelet algorithm is Nlog₂N. Obviously, if the wavelet algorithm does not do better than this simple algorithm for the data set in question, the wavelet is a poor choice (or, perhaps, the wavelet function in the predict step is poorly chosen for the data set).

Definition at line 35 of file delta.h.

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Member Function Documentation

template<class T> void delta_trans<T>::forward ( T * vec, size_t len ) [inline]

Convert the value in the array into an initial reference value and a set of delta values. Definition at line 42 of file delta.h. Referenced by delta_calc(). { if (vec != 0 && len > 0) { // reference value T next; T refVal = vec[0]; for (size_t i = 1; i < len; i++) { next = vec[i]; vec[i] = vec[i] - refVal; refVal = next; } } } // forward

template<class T> void delta_trans<T>::inverse ( T * vec, size_t len ) [inline]

Definition at line 57 of file delta.h. Referenced by delta_calc(). { if (vec != 0 && len > 0) { for (size_t i = 1; i < len; i++) { vec[i] = vec[i] + vec[i-1]; } } } // inverse

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The documentation for this class was generated from the following file:

• delta.h

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