# Command: typebind

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Name:

    typebind - optimizes procedure for certain data type

Synopsis:

    proc dict typebind -> proc

Examples:

      The following is the closed form expression of a postsynaptic potential at
      at time t

      (
      weight * E/tau_syn * 1./C_m
      * (   (exp(-t/tau_m)-exp(-t/tau_syn)) / (1./tau_syn	- 1./tau_m)^2.
      -	 t*exp(-t/tau_syn)	 / (1./tau_syn	- 1./tau_m)
      )
      )
      CompileMath /v Set

      The expression operates on doubles. Therefore we optimize with

      /v load
      <<
      /add [/doubletype /doubletype]
      /sub [/doubletype /doubletype]
      /mul [/doubletype /doubletype]
      /div [/doubletype /doubletype]
      /pow [/doubletype /doubletype]
      /exp [/doubletype ]
      /neg [/doubletype ]
      >> typebind /v_d Set

      We can further optimize by replacing all symbolic constants by the
      corresponding values

      /v_d load
      <<
      /weight   3.2
      /tau_syn   0.5
      /tau_m   10.0
      /C_m	 250.0
      /t	 1.345
      /E	 E
      >> Inline /v_c Set

      Let us now explore the required number of interpreter cycles and the run time
      of the three versions

      clic v cloc
      clic v_d cloc
      clic v_c cloc
      tic 500000 {v pop}   repeat toc
      tic 500000 {v_d pop} repeat toc
      tic 500000 {v_c pop} repeat toc

      The results are:
      v   v_d   v_c
      ----------------------------------
      cycles	 138   112   97
      reduction factor	 1.2   1.4
      20%   30%
      ----------------------------------
      time	 20.8  8.3   6.5
      reduction factor	 2.5   3.2
      60%   69%
      ----------------------------------

Description:

      The operator is called on a procedure and optimizes the function
      calls in this procedure by removing type checking of the overloaded
      functions according to the information in the dictionary. The dictionary
      specifies the names of the functions for which the type of the arguments
      is knon and the expected combination of argument types. typebind uses this
      information to replace the function calls in the procedure by the appropriate
      variant. This reduces the number of interpreter cycles required to evaluate
      the procedure. However, the bigger effect is the reduction of run time.
      The operator typebind can be used to optimize SLI code for speed in
      situations where it is guaranteed that a particular variant of a
      function is needed. Here, replacing the overloaded function by the
      specific variant removes the overhead of type checking. A typical
      situation in which the data types of the arguments are known is a
      function call inside a function with a specified signature (see
      example below). Another situation is machine generated SLI code where
      the machine, for example a compiler, is requested to emit optimized
      code restricted to particular data type.

      /incr [/doubletype]
      {
      1.0 add
      }
      << /add [/doubletype /doubletype] >> typebind
      def

      The example below achieves a reduction of interpreter cycles by 20%
      but a reduction of rune time by 60%.

Parameters:

      proc, is the procedure to be optimized
      dict, contains as keys the names of the operators that should
      be constrained to a certain combination of argument types.
      The value associated to the key is an array specifying the
      data type of each argument.

Remarks:

      typebind may be implemented by Inline, see the documentation of variant.

Author:

    Diesmann

FirstVersion:

    090210

SeeAlso:

- variant
- Inline
- CompileMath
- def
- clic
- tic

Source:

    /opt/conda/conda-bld/nest_1510212701067/work/nest-2.14.0/lib/sli/typeinit.sli

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