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******************************************************************************/
/* This file is part of MAPMAKER 3.0b, Copyright 1987-1992, Whitehead Institute
   for Biomedical Research. All rights reserved. See READ.ME for license. */

/* Eqn is broken up into 2 major parts.  Make_equation takes an 
inputted equation and converts it to an array of structures in reverse
polish notation, and evaluate_equation evlautes the equation over a set
of points ***/


/* This is the data structure that I propose to use.  It is basically 
made up of two parts - is_a which is a flag that can have three 
possible values, SYMBOL, VARIABLE, or NUMBER, which indicate what the 
union is storing. I will use an array of pointers to these structures
of MAX_EQN_SIZE 500.  When sending this array to the function 
make_equation, a ** pointer to the array of pointers is used.*/
                    
#define MAX_EQN_SIZE 500 /* this setting means the largest equation we
			    can handle is about 100 characters      */

typedef struct {                  
    int is_a;  
    union {         
       	int variable;
       	int symbol;
      	real number;
    } val;
} EQUATION;

#define SYMBOL -1           /* these are flags          */
#define VARIABLE 2          /* to be used in the        */
#define NUMBER 1            /* data structures EQUATION */

#define PLUS 1
#define MINUS 2
#define MULTIPLY 3
#define DIVIDE 4
#define EXP 5
#define LOG 6
#define LN 7
#define SIN 8
#define ASIN 9
#define COS 10
#define ACOS 11
#define TAN 12
#define ATAN 13
#define LEFT_P 14
#define RIGHT_P 15
extern char **variable_table;
extern real *value_table;                   
void eqn_init();  /* Takes no arguments, it mallocs pasred and temp_eqn */
extern int table_size;
real value_lookup();
int variable_lookup();
/**************** The make equation subroutine ***********************/

EQUATION **make_equation();
 
/**** args:  char *original_eqn, char **symbol_table, int table_len 
  inputted_eqn is a char pointer to the equation as inputted by the
  user, **symbol_table is a pointer to an array of chars that contains
  all variables in the expression, and table_len is the length of the
  symbol table  ********/ 

/* The subroutine  **make_equation takes the inputted equation, and
   converts it to an array of structures.  It returns a pointer to the
   array of pointers.  */

/*  Error handling - if an error occurs in make_equation, a string is 
    set that will tell what the error is will be sent to the routine send,
    which is a back-checking routine.  If the occurs, I will also free all
    arrays and pointers that have been malloced, and reinitialize all 
    internal variables */

/******************* evaluating the equation ************************/

real evaluate_equation();

/** args: ELEMENT **parsed_equation, real *variable_values
  parsed_equation is the pointer to the array of pointers to the
  structures, and variable_value contains the value of each 
  variable in the equation. ******/ 

/* Error handling - if a math error occurs, this will send the message
   MATHERR, if any other type of error occurs, then it probably a coding
   error that will have to be looked at, so the message CRASH will be sent*/

/* Various important global variables */

#define SIZEOF_STACK 100
extern int stack_pointer;
real val[SIZEOF_STACK];
int eqnlen;
int table_size;
char **variable_table;
real *value_table;