litex/migen/fhdl/bitcontainer.py

203 lines
4.8 KiB
Python

from migen.fhdl import structure as f
def log2_int(n, need_pow2=True):
l = 1
r = 0
while l < n:
l *= 2
r += 1
if need_pow2 and l != n:
raise ValueError("Not a power of 2")
return r
def bits_for(n, require_sign_bit=False):
if n > 0:
r = log2_int(n + 1, False)
else:
require_sign_bit = True
r = log2_int(-n, False)
if require_sign_bit:
r += 1
return r
def value_bits_sign(v):
if isinstance(v, bool):
return 1, False
elif isinstance(v, int):
return bits_for(v), v < 0
elif isinstance(v, f.Signal):
return v.nbits, v.signed
elif isinstance(v, (f.ClockSignal, f.ResetSignal)):
return 1, False
elif isinstance(v, f._Operator):
obs = list(map(value_bits_sign, v.operands))
if v.op == "+" or v.op == "-":
if not obs[0][1] and not obs[1][1]:
# both operands unsigned
return max(obs[0][0], obs[1][0]) + 1, False
elif obs[0][1] and obs[1][1]:
# both operands signed
return max(obs[0][0], obs[1][0]) + 1, True
elif not obs[0][1] and obs[1][1]:
# first operand unsigned (add sign bit), second operand signed
return max(obs[0][0] + 1, obs[1][0]) + 1, True
else:
# first signed, second operand unsigned (add sign bit)
return max(obs[0][0], obs[1][0] + 1) + 1, True
elif v.op == "*":
if not obs[0][1] and not obs[1][1]:
# both operands unsigned
return obs[0][0] + obs[1][0]
elif obs[0][1] and obs[1][1]:
# both operands signed
return obs[0][0] + obs[1][0] - 1
else:
# one operand signed, the other unsigned (add sign bit)
return obs[0][0] + obs[1][0] + 1 - 1
elif v.op == "<<<":
if obs[1][1]:
extra = 2**(obs[1][0] - 1) - 1
else:
extra = 2**obs[1][0] - 1
return obs[0][0] + extra, obs[0][1]
elif v.op == ">>>":
if obs[1][1]:
extra = 2**(obs[1][0] - 1)
else:
extra = 0
return obs[0][0] + extra, obs[0][1]
elif v.op == "&" or v.op == "^" or v.op == "|":
if not obs[0][1] and not obs[1][1]:
# both operands unsigned
return max(obs[0][0], obs[1][0]), False
elif obs[0][1] and obs[1][1]:
# both operands signed
return max(obs[0][0], obs[1][0]), True
elif not obs[0][1] and obs[1][1]:
# first operand unsigned (add sign bit), second operand signed
return max(obs[0][0] + 1, obs[1][0]), True
else:
# first signed, second operand unsigned (add sign bit)
return max(obs[0][0], obs[1][0] + 1), True
elif v.op == "<" or v.op == "<=" or v.op == "==" or v.op == "!=" \
or v.op == ">" or v.op == ">=":
return 1, False
elif v.op == "~":
return obs[0]
else:
raise TypeError
elif isinstance(v, f._Slice):
return v.stop - v.start, value_bits_sign(v.value)[1]
elif isinstance(v, f.Cat):
return sum(value_bits_sign(sv)[0] for sv in v.l), False
elif isinstance(v, f.Replicate):
return (value_bits_sign(v.v)[0])*v.n, False
elif isinstance(v, f._ArrayProxy):
bsc = list(map(value_bits_sign, v.choices))
return max(bs[0] for bs in bsc), any(bs[1] for bs in bsc)
else:
raise TypeError("Can not calculate bit length of {} {}".format(
type(v), v))
def flen(v):
"""Bit length of an expression
Parameters
----------
v : int, bool or Value
Returns
-------
int
Number of bits required to store `v` or available in `v`
Examples
--------
>>> flen(f.Signal(8))
8
>>> flen(0xaa)
8
"""
return value_bits_sign(v)[0]
def fiter(v):
"""Bit iterator
Parameters
----------
v : int, bool or Value
Returns
-------
iter
Iterator over the bits in `v`
Examples
--------
>>> list(fiter(f.Signal(2))) #doctest: +ELLIPSIS
[<migen.fhdl.structure._Slice object at 0x...>, <migen.fhdl.structure._Slice object at 0x...>]
>>> list(fiter(4))
[0, 0, 1]
"""
if isinstance(v, (bool, int)):
return ((v >> i) & 1 for i in range(bits_for(v)))
elif isinstance(v, f.Value):
return (v[i] for i in range(flen(v)))
else:
raise TypeError("Can not bit-iterate {} {}".format(type(v), v))
def fslice(v, s):
"""Bit slice
Parameters
----------
v : int, bool or Value
s : slice or int
Returns
-------
int or Value
Expression for the slice `s` of `v`.
Examples
--------
>>> fslice(f.Signal(2), 1) #doctest: +ELLIPSIS
<migen.fhdl.structure._Slice object at 0x...>
>>> bin(fslice(0b1101, slice(1, None, 2)))
'0b10'
>>> fslice(-1, slice(0, 4))
1
>>> fslice(-7, slice(None))
9
"""
if isinstance(v, (bool, int)):
if isinstance(s, int):
s = slice(s)
idx = range(*s.indices(bits_for(v)))
return sum(((v >> i) & 1) << j for j, i in enumerate(idx))
elif isinstance(v, f.Value):
return v[s]
else:
raise TypeError("Can not bit-slice {} {}".format(type(v), v))
def freversed(v):
"""Bit reverse
Parameters
----------
v : int, bool or Value
Returns
-------
int or Value
Expression containing the bit reversed input.
Examples
--------
>>> freversed(f.Signal(2)) #doctest: +ELLIPSIS
<migen.fhdl.structure.Cat object at 0x...>
>>> bin(freversed(0b1011))
'0b1101'
"""
return fslice(v, slice(None, None, -1))