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The following procedure should be used in a program that maintains an index into a string, beginning at character zero (0). The program calls this procedure to get the next character and to update the index, based on how many characters were used to represent the Gensym character set character.

This pseudocode procedure gets the character code for the Gensym character set character at position i in string s; that is, s(i).

1. Let c be the character s(i). Let i = i + 1.

2. If:
   • c is the character @, then let c be the character s(i) and i = i + 1.

   • c is the character L, then return the character code or codes for newline.

   • c is an alphabetic character, then consider this to be an undefined situation (that is, an error) and exit.

   Otherwise, return the ASCII character code for c. The result is an ASCII-encoded character.

3. If:
   • c is the character ~, then let c be the character s(i) and i = i + 1.

   • c is not in the table Encoding for ASCII and Special Characters, then consider this to be an undefined situation (that is, an error) and exit.

   Otherwise, return the character code or codes for the character that c corresponds to in the table Encoding for ASCII and Special Characters. This result might be in ASCII or in some other (undefined) character encoding. Note that the characters ~ @ and \ are included in this set.

4. If:
   • c is the character \, then let c be the character s(i) and i = i + 1.

   • The character code for c is less than 40, then let d1 = the character code for c, let d2 = the character code for s(i), let i = i + 1, let d3 = s(i), and return the result of the following formula:

     /* arithmetically shift d1 left 13 bits */ 
     (d1 << 13)      
     + (d2 * 95) 
     + d3 
     + -265976 

   Otherwise, let d1 = the character code for c, let d2 = the character code for s(i), let i = i + 1, and return the result of the following formula:

   (d1 * 95) 
   + d2 
   + 4360 

   The result is a JIS-encoded character.

5. Return the code for c. The result is an ASCII-encoded character.

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