tools/base_converter.py

   1 #!env python
   2 # vim: set fileencoding=utf8
   3 # Created: April 29, 2008
   4 # Created by: Antonio Chavez
   5 #
   6 # Base converter
   7
   8 import sys, os
   9 import Trits
  10
  11 MIN_VAL = 10
  12 LOW_BOUND = ord('A') + MIN_VAL
  13
  14 def int_cnvrt(value, base_frm, base_to):
  15     ''' int_cvrt: convert the number to the left of the decimal place
  16         value: string containing value to convert
  17         from: what base to convert from. Can be positive and negative.
  18             Negative numbers will represent balanced base.  Positive
  19             will represent unbalanced base.
  20         to: what base to convert to.
  21
  22         Example: 3 = unbalanced base 3 (0, 1, 2)
  23                 -3 = balanced base 3 (-1, 0, 1)
  24         Balanced bases can only be odd integers, for the obivious reason
  25             that even numbers are not good candidates for balanced numbering
  26             Example: -4 = (-1, 0, 1, 2) or (-2, -1, 0, 1).  Either system is
  27             not balanced.  Bases must also have a magnitude greater than 1.
  28         For balanced bases greater than 3, a negative number is represented
  29             with an 'i' next to it.
  30             Example: 4i21 => 4(-2)1
  31         Currently conversion balanced bases is not supported.  If balanced
  32             base is entered, the result will be returned in base 10.
  33         A negative sign before the number will negate the result.
  34     '''
  35
  36     # check for magnitude greater than 1
  37     if abs(base_frm) < 2 or abs(base_to) < 2:
  38         print "bases must have magnitude greater than 1"
  39         raise SystemExit
  40
  41     # check for a balanced negative base and derive magnitude
  42     if base_frm < 0 and base_frm*-1%2 != 1:
  43         print "base_from is even: negative bases must be odd integers"
  44         raise SystemExit
  45     elif base_frm < 0:
  46         magnitude_f = (base_frm*-1 - 1)/2
  47     else:
  48         magnitude_f = base_frm
  49
  50     if base_to < 0 and base_to*-1%2 != 1:
  51         print "base_to is even: negative bases must be odd integers"
  52         raise SystemExit
  53     elif base_to < 0:
  54         magnitude_t = (base_to*-1 - 1)/2
  55     else:
  56         magnitude_t = base_to
  57
  58     sum   = 0   # base 10 equivalent summation
  59     neg   = 1   # used when 'i' is encountered, it negates the previous digit
  60     sign  = 1   # sign of summation
  61     count = 1   # amount to multiply next digit by
  62     prev  = 1   # the value of the next digit
  63     cur   = 0   # current digit
  64
  65     if magnitude_f >= MIN_VAL:
  66         max_val = magnitude_f - MIN_VAL
  67
  68     for i in range(len(value) - 1, -1, -1):
  69
  70         if abs(base_frm) == 3:
  71             # Base 3 conversion
  72             if value[i] in Trits.trit_integer:
  73                 sum = sum + Trits.trit_integer[value[i]]*count
  74                 count = count*abs(base_frm)
  75             else:
  76                 print "%s invalid input", value[i]
  77                 raise SystemExit
  78
  79         elif value[i].isdigit():
  80             # 0 <-> 9
  81             cur = int(value[i])
  82
  83             if cur > magnitude_f:
  84                 print "%s: invalid input", value[i]
  85                 raise SystemExit
  86             if i != len(value) -1:
  87                 sum = sum + prev*neg*count
  88
  89                 # reset variables to appropiate values
  90                 neg = 1
  91                 count = count*abs(base_frm)
  92
  93             prev = cur
  94
  95         elif value[i] == '-' and i == len(value) - 1:
  96             # negate the whole number
  97             sign = -1
  98         elif value[i] == 'i':
  99             # negate prev number
 100             neg = -1
 101         elif magnitude_f >= MIN_VAL and value[i].isalpha():
 102             # 10 <-> magnitude_f
 103             cur = ord(value[i].upper()) - LOW_BOUND
 104
 105             if cur > magnitude_f:
 106                 print "%s: invalid input", value[i]
 107                 raise SystemExit
 108
 109             if i != len(value) -1:
 110                 sum = sum + prev*neg*count
 111
 112                 # reset variables to appropriate values
 113                 neg = 1
 114                 count = count*abs(base_frm)
 115
 116             prev = cur
 117
 118         else:
 119             print "%s: invalid input", value[i]
 120             raise SystemExit
 121
 122     # sum up remaining digit
 123     sum = sum + prev*neg*count
 124     sum = sign*sum
 125
 126     # return base 10 if desired base is balanced
 127     if base_frm < 0:
 128         return "" + sum
 129
 130     # compute unbalanced conversion
 131     result = ""
 132     quotient = sum
 133     remainder = 0
 134
 135     while quotient != 0:
 136         remainder = quotient%magnitude_t
 137         quotient = quotient/magnitude_t
 138         result = str(remainder) + result
 139
 140     return result
 141
 142 ''' NOTES
 143     useful things to know for implementation
 144     char to int: ord('a') = 97 ASCII
 145     int to char: chr(97)  ASCII
 146     char to int: int('4')
 147     a = "hi6"
 148     a[0].isalpha() => true
 149     a[2].isdigit() => true
 150     a[0].upper()   => "H"
 151     a[2].upper()   => "1"
 152
 153     s.split(".")   => returns list of strings broken up by "."
 154     "1010.3930"    => ["1010", "3930"]
 155
 156     s = ".".join(lis_digits) => combine elements in list by "."
 157 '''
 158
 159 if __name__ == "__main__":
 160     print int_cnvrt("10i", -3, 10)