☜	Numeric Interpretation 1977 Version of ANSI Standard					☞

3.2.5 Numeric Interpretation of Data

Certain operations, such as arithmetic, deal with the numeric interpretations of their operands. The numeric interpretation is a mapping from the set of all data values onto the set of all numeric values, described by the following algorithm. Note that the numeric interpretation maps numeric values onto themselves.

(Note: The "head" of a string is defined to be a substring which contains all of the characters of the string to the left of a given point and none of the characters of the string to the right of that point. A head may be empty or it may be the entire string.)

Consider the argument to be the string S.

First, apply the following sign reduction rules to S as many times as possible, in any order.

1. If S is of the form + T, then remove the +.
   (Shorthand: + T T)
2. - + T - T
3. - - T T

Second, apply one of the following, as appropriate.

1. If the leftmost character of S is not "-", form the longest head of S which satisfies the syntax description of numlit. Then apply the algorithm of 3.2.4.2 to the result.
2. If S is of the form - T, apply step a. above to T and append a "-" to the left of the result. If the result is "–0", change it to "0".>

The "numeric expression" numexpr is defined to have the same syntax as expr. Its presence in a syntax description serves to indicate that the numeric interpretation of its value is to be taken when it is executed.

See also the transition diagram for numexpr.

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Copyright © Annotations: 2008-2024 Ed de Moel.

This page most recently updated on 12-Sep-2014, 13:11:21.

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