State machine

gistfile1.js

var GO    = 'GO',
    OK    = 'OK',
    SIGN  = 'SIGN',
    LZERO = 'LZERO',
    INT   = 'INT',
    FRAC  = 'FRAC',
    FDIG  = 'FDIG',
    EXP   = 'EXP',
    XSIGN = 'XSIGN',
    EDIG  = 'EDIG',
    __    = -1;
    
var VALUE_MAP = {
   '+'  : 0, '-'  : 1, '.'  : 2,  
   'e'  : 3, 'E'  : 3, '0'  : 4,  
   '1'  : 5, '2'  : 5, '3'  : 5,  
   '4'  : 5, '5'  : 5, '6'  : 5,
   '7'  : 5, '8'  : 5, '9'  : 5,
   ' '  : 6, '\t' : 6, '\r' : 6,
   '\n' : 6 
};
var ETC = 7;
/**
 * Transition table for 
 * JSON numbers
 * http://json.org/
 */
var PTBL = {
/*           |  +  |  -  | .  |e-E|   0 |1-9 |SPACE| ETC  */
     GO    : [__   ,SIGN ,__  ,__ ,LZERO,INT ,__   ,__],
     SIGN  : [__   ,__   ,__  ,__ ,LZERO,INT ,__   ,__],
     LZERO : [__   ,__   ,FRAC,EXP,__   ,__  ,OK   ,__],
     INT   : [__   ,__   ,FRAC,EXP,INT  ,INT ,OK   ,__],
     
     FRAC  : [__   ,__   ,__  ,__ ,FDIG ,FDIG,__   ,__],
     FDIG  : [__   ,__   ,__  ,EXP,FDIG ,FDIG,OK   ,__],
     
     EXP   : [XSIGN,XSIGN,__  ,__ ,EDIG ,EDIG,__   ,__],
     XSIGN : [__   ,__   ,__  ,__ ,EDIG ,EDIG,__   ,__],
     EDIG  : [__   ,__   ,__  ,__ ,EDIG ,EDIG,OK   ,__]    
};


function parse(source) {
    var state = GO,
        len = source.length,
        col;
    source += ' ';   
    for (var i = 0; i <= len && state != __; i++) {
        col = VALUE_MAP[source.charAt(i)];
        col = col >= 0 ? col : ETC;
        state = PTBL[state][col];   
    }
    if (state == __) {
        throw 'Invalid token - ' + source.slice(0, i);
    }
    return source.slice(0, i - 1);
}

//Example inputs
parse('3.142857142857143');
parse('137');
parse('-1');
parse('6.67e-11');
parse('-1.127e20');