migen/fhdl/bitcontainer.py

   1 from migen.fhdl import structure as f
   2
   3
   4 __all__ = ["log2_int", "bits_for", "flen", "fiter"]
   5
   6
   7 def log2_int(n, need_pow2=True):
   8     l = 1
   9     r = 0
  10     while l < n:
  11         l *= 2
  12         r += 1
  13     if need_pow2 and l != n:
  14         raise ValueError("Not a power of 2")
  15     return r
  16
  17
  18 def bits_for(n, require_sign_bit=False):
  19     if n > 0:
  20         r = log2_int(n + 1, False)
  21     else:
  22         require_sign_bit = True
  23         r = log2_int(-n, False)
  24     if require_sign_bit:
  25         r += 1
  26     return r
  27
  28
  29 def value_bits_sign(v):
  30     if isinstance(v, (f.Constant, f.Signal)):
  31         return v.nbits, v.signed
  32     elif isinstance(v, (f.ClockSignal, f.ResetSignal)):
  33         return 1, False
  34     elif isinstance(v, f._Operator):
  35         obs = list(map(value_bits_sign, v.operands))
  36         if v.op == "+" or v.op == "-":
  37             if not obs[0][1] and not obs[1][1]:
  38                 # both operands unsigned
  39                 return max(obs[0][0], obs[1][0]) + 1, False
  40             elif obs[0][1] and obs[1][1]:
  41                 # both operands signed
  42                 return max(obs[0][0], obs[1][0]) + 1, True
  43             elif not obs[0][1] and obs[1][1]:
  44                 # first operand unsigned (add sign bit), second operand signed
  45                 return max(obs[0][0] + 1, obs[1][0]) + 1, True
  46             else:
  47                 # first signed, second operand unsigned (add sign bit)
  48                 return max(obs[0][0], obs[1][0] + 1) + 1, True
  49         elif v.op == "*":
  50             if not obs[0][1] and not obs[1][1]:
  51                 # both operands unsigned
  52                 return obs[0][0] + obs[1][0], False
  53             elif obs[0][1] and obs[1][1]:
  54                 # both operands signed
  55                 return obs[0][0] + obs[1][0] - 1, True
  56             else:
  57                 # one operand signed, the other unsigned (add sign bit)
  58                 return obs[0][0] + obs[1][0] + 1 - 1, True
  59         elif v.op == "<<<":
  60             if obs[1][1]:
  61                 extra = 2**(obs[1][0] - 1) - 1
  62             else:
  63                 extra = 2**obs[1][0] - 1
  64             return obs[0][0] + extra, obs[0][1]
  65         elif v.op == ">>>":
  66             if obs[1][1]:
  67                 extra = 2**(obs[1][0] - 1)
  68             else:
  69                 extra = 0
  70             return obs[0][0] + extra, obs[0][1]
  71         elif v.op == "&" or v.op == "^" or v.op == "|":
  72             if not obs[0][1] and not obs[1][1]:
  73                 # both operands unsigned
  74                 return max(obs[0][0], obs[1][0]), False
  75             elif obs[0][1] and obs[1][1]:
  76                 # both operands signed
  77                 return max(obs[0][0], obs[1][0]), True
  78             elif not obs[0][1] and obs[1][1]:
  79                 # first operand unsigned (add sign bit), second operand signed
  80                 return max(obs[0][0] + 1, obs[1][0]), True
  81             else:
  82                 # first signed, second operand unsigned (add sign bit)
  83                 return max(obs[0][0], obs[1][0] + 1), True
  84         elif v.op == "<" or v.op == "<=" or v.op == "==" or v.op == "!=" \
  85           or v.op == ">" or v.op == ">=":
  86               return 1, False
  87         elif v.op == "~":
  88             return obs[0]
  89         else:
  90             raise TypeError
  91     elif isinstance(v, f._Slice):
  92         return v.stop - v.start, value_bits_sign(v.value)[1]
  93     elif isinstance(v, f.Cat):
  94         return sum(value_bits_sign(sv)[0] for sv in v.l), False
  95     elif isinstance(v, f.Replicate):
  96         return (value_bits_sign(v.v)[0])*v.n, False
  97     elif isinstance(v, f._ArrayProxy):
  98         bsc = list(map(value_bits_sign, v.choices))
  99         return max(bs[0] for bs in bsc), any(bs[1] for bs in bsc)
 100     else:
 101         raise TypeError("Can not calculate bit length of {} {}".format(
 102             type(v), v))
 103
 104
 105 def flen(v):
 106     """Bit length of an expression
 107
 108     Parameters
 109     ----------
 110     v : int, bool or Value
 111
 112     Returns
 113     -------
 114     int
 115         Number of bits required to store `v` or available in `v`
 116
 117     Examples
 118     --------
 119     >>> flen(f.Signal(8))
 120     8
 121     >>> flen(0xaa)
 122     8
 123     """
 124     return value_bits_sign(v)[0]
 125
 126
 127 def fiter(v):
 128     """Bit iterator
 129
 130     Parameters
 131     ----------
 132     v : int, bool or Value
 133
 134     Returns
 135     -------
 136     iter
 137         Iterator over the bits in `v`
 138
 139     Examples
 140     --------
 141     >>> list(fiter(f.Signal(2))) #doctest: +ELLIPSIS
 142     [<migen.fhdl.structure._Slice object at 0x...>, <migen.fhdl.structure._Slice object at 0x...>]
 143     >>> list(fiter(4))
 144     [0, 0, 1]
 145     """
 146     if isinstance(v, (bool, int)):
 147         return ((v >> i) & 1 for i in range(bits_for(v)))
 148     elif isinstance(v, f.Value):
 149         return (v[i] for i in range(flen(v)))
 150     else:
 151         raise TypeError("Can not bit-iterate {} {}".format(type(v), v))