Class: VHDL_Parser::Utility

Inherits:
Object
  • Object
show all
Defined in:
lib/vhdl_parser/utility.rb

Overview

Utility class with helpers

Class Method Summary collapse

Class Method Details

.sub_constants(target, key, value) ⇒ Object

Substitutes a constant with an actual value, and does so smartly. This method uses the ‘eval` method to evaluate the final Math expression into a single value. It does some basic input checking and replaces everything that’s not a number or mathematical operator with “x”. That should prevent some abuse.

Parameters:

  • String (target) —

    The size string, e.g. “MY_VALUE-1”

  • String (key) —

    The key string, e.g. “MY_VALUE”. This gets compared to the target.

  • String (value) —

    The value string, e.g. “8”. That’s what MY_VALUE gets replaced with.



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# File 'lib/vhdl_parser/utility.rb', line 14

def self.sub_constants(target, key, value)
  # first get all the words of the size. That could be
  # a number or a constant.
  words = target.to_s.scan /\w+/
  ret = ""  
  words.each do |w|
    # if a word matches the key and it's not numeric, it must 
    # be a constant that we want to replace
    if w.eql?(key) and not w.is_numeric?
      # so replace it here with the given value
      ret = target.gsub(w,value).to_s
    end
  end

  # now eval the result. If a constant has been replaced with a 
  # value, it could be something like "8-1", so eval that into 7.
  # In case it's still a constant, catch the NameError but ignore it;
  # chances are the constant will be replaced later.
  begin
    # since we're eval'ing here, do some basic cleanup to prevent badness.
    # Specifically, replace anything that's not a number or basic math
    # function with 'xx', since those should trigger the exception anyway.
    foreval = ret.gsub(/[^-+*\/\d\(\)\s]/,'xx')
    ret = eval(foreval)
  rescue NameError => e
  end
  # if nothing was replaced, we get nil, so instead of returning nil,
  # just return the original target, meaning this was just a noop.
  ret.nil? ? target.to_s : ret
end