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Base Type Requirements for Hash Coding Values
Syntax
`code = hash_code(x)`
Purpose
CppAD uses a table of `Base` type values when recording `AD<Base>` operations. A hashing function is used to reduce number of values stored in this table; for example, it is not necessary to store the value 3.0 every time it is used as a parameter .
Default
The default hashing function works with the set of bits that correspond to a `Base` value. In most cases this works well, but in some cases it does not. For example, in the base_adolc.hpp case, an `adouble` value can have fields that are not initialized and `valgrind` reported an error when these are used to form the hash code.
x
This argument has prototype `
const Base& x
` It is the value we are forming a hash code for.
code
The return value `code` has prototype `
unsigned short code
` It is the hash code corresponding to `x` . This intention is the commonly used values will have different hash codes. The hash code must satisfy `
code < CPPAD_HASH_TABLE_SIZE
` so that it is a valid index into the hash code table.
inline
If you define this function, it should declare it to be `inline`, so that you do not get multiple definitions from different compilation units.
Example
See the `base_alloc` hash_code and the `adouble` hash_code .

Input File: cppad/core/base_hash.hpp