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Introduction to Shift-and-Add Algorithms

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Elementary Functions

Abstract

We present the simplest shift-and-add algorithms and the notions that will be useful for designing more sophisticated algorithms.

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Notes

  1. 1.

    In this estimation, we do not take the rounding errors into account. They will depend on the precision used for representing the intermediate variables of the algorithm.

  2. 2.

    In this estimation, we do not take the rounding errors into account. They will depend on the precision used for representing the intermediate variables of the algorithm.

  3. 3.

    If \(d_n\) was chosen by means of a comparison, computation would be slowed down — the time saved by performing fully parallel additions would be lost — and huge tables would be required if \(d_n\) was given by a table lookup — and, incidentally, if we were able to implement such huge tables efficiently, we would rather directly tabulate the exponential function.

  4. 4.

    Remember, \(L_{n}^{*}\) is a multiple of 1 / 2; therefore \(L_{n}^{*} > -1\) implies \(L_{n}^{*} \ge -1/2\).

  5. 5.

    Since \(L_n^*\) is a multiple of 1 / 2, “\(-1/2 \le L_n^* \le 0\)” is equivalent to “\(L_n^* \in \{-1/2,0\}\).”

  6. 6.

    Using a modified CORDIC algorithm; CORDIC is presented in the next chapter.

  7. 7.

    This can be viewed as the possible use of \(d_{i}=2\) for a few values of i, or as the use of a new discrete base, obtained by repeating a few terms of the sequence \((w_{i})\).

  8. 8.

    That is, \(0 \le x_0 \le \sum _{k=0}^{\infty }w_k\).

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Correspondence to Jean-Michel Muller .

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© 2016 Springer Science+Business Media New York

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Muller, JM. (2016). Introduction to Shift-and-Add Algorithms. In: Elementary Functions. Birkhäuser, Boston, MA. https://doi.org/10.1007/978-1-4899-7983-4_8

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