-
-class PartitionPoints(dict):
- """Partition points and corresponding ``Value``s.
-
- The points at where an ALU is partitioned along with ``Value``s that
- specify if the corresponding partition points are enabled.
-
- For example: ``{1: True, 5: True, 10: True}`` with
- ``width == 16`` specifies that the ALU is split into 4 sections:
- * bits 0 <= ``i`` < 1
- * bits 1 <= ``i`` < 5
- * bits 5 <= ``i`` < 10
- * bits 10 <= ``i`` < 16
-
- If the partition_points were instead ``{1: True, 5: a, 10: True}``
- where ``a`` is a 1-bit ``Signal``:
- * If ``a`` is asserted:
- * bits 0 <= ``i`` < 1
- * bits 1 <= ``i`` < 5
- * bits 5 <= ``i`` < 10
- * bits 10 <= ``i`` < 16
- * Otherwise
- * bits 0 <= ``i`` < 1
- * bits 1 <= ``i`` < 10
- * bits 10 <= ``i`` < 16
- """
-
- def __init__(self, partition_points=None):
- """Create a new ``PartitionPoints``.
-
- :param partition_points: the input partition points to values mapping.
- """
- super().__init__()
- if partition_points is not None:
- for point, enabled in partition_points.items():
- if not isinstance(point, int):
- raise TypeError("point must be a non-negative integer")
- if point < 0:
- raise ValueError("point must be a non-negative integer")
- self[point] = Value.wrap(enabled)
-
- def like(self, name=None, src_loc_at=0, mul=1):
- """Create a new ``PartitionPoints`` with ``Signal``s for all values.
-
- :param name: the base name for the new ``Signal``s.
- :param mul: a multiplication factor on the indices
- """
- if name is None:
- name = Signal(src_loc_at=1+src_loc_at).name # get variable name
- retval = PartitionPoints()
- for point, enabled in self.items():
- point *= mul
- retval[point] = Signal(enabled.shape(), name=f"{name}_{point}")
- return retval
-
- def eq(self, rhs):
- """Assign ``PartitionPoints`` using ``Signal.eq``."""
- if set(self.keys()) != set(rhs.keys()):
- raise ValueError("incompatible point set")
- for point, enabled in self.items():
- yield enabled.eq(rhs[point])
-
- def as_mask(self, width, mul=1):
- """Create a bit-mask from `self`.
-
- Each bit in the returned mask is clear only if the partition point at
- the same bit-index is enabled.
-
- :param width: the bit width of the resulting mask
- :param mul: a "multiplier" which in-place expands the partition points
- typically set to "2" when used for multipliers
- """
- bits = []
- for i in range(width):
- i /= mul
- if i.is_integer() and int(i) in self:
- bits.append(~self[i])
- else:
- bits.append(True)
- return Cat(*bits)
-
- def get_max_partition_count(self, width):
- """Get the maximum number of partitions.
-
- Gets the number of partitions when all partition points are enabled.
- """
- retval = 1
- for point in self.keys():
- if point < width:
- retval += 1
- return retval
-
- def fits_in_width(self, width):
- """Check if all partition points are smaller than `width`."""
- for point in self.keys():
- if point >= width:
- return False
- return True
-
- def part_byte(self, index, mfactor=1): # mfactor used for "expanding"
- if index == -1 or index == 7:
- return C(True, 1)
- assert index >= 0 and index < 8
- return self[(index * 8 + 8)*mfactor]
-
-
-class FullAdder(Elaboratable):
- """Full Adder.
-
- :attribute in0: the first input
- :attribute in1: the second input
- :attribute in2: the third input
- :attribute sum: the sum output
- :attribute carry: the carry output
-
- Rather than do individual full adders (and have an array of them,
- which would be very slow to simulate), this module can specify the
- bit width of the inputs and outputs: in effect it performs multiple
- Full 3-2 Add operations "in parallel".
- """
-
- def __init__(self, width):
- """Create a ``FullAdder``.
-
- :param width: the bit width of the input and output
- """
- self.in0 = Signal(width, reset_less=True)
- self.in1 = Signal(width, reset_less=True)
- self.in2 = Signal(width, reset_less=True)
- self.sum = Signal(width, reset_less=True)
- self.carry = Signal(width, reset_less=True)
-
- def elaborate(self, platform):
- """Elaborate this module."""
- m = Module()
- m.d.comb += self.sum.eq(self.in0 ^ self.in1 ^ self.in2)
- m.d.comb += self.carry.eq((self.in0 & self.in1)
- | (self.in1 & self.in2)
- | (self.in2 & self.in0))
- return m
-
-
-class MaskedFullAdder(Elaboratable):
- """Masked Full Adder.
-
- :attribute mask: the carry partition mask
- :attribute in0: the first input
- :attribute in1: the second input
- :attribute in2: the third input
- :attribute sum: the sum output
- :attribute mcarry: the masked carry output
-
- FullAdders are always used with a "mask" on the output. To keep
- the graphviz "clean", this class performs the masking here rather
- than inside a large for-loop.
-
- See the following discussion as to why this is no longer derived
- from FullAdder. Each carry is shifted here *before* being ANDed
- with the mask, so that an AOI cell may be used (which is more
- gate-efficient)
- https://en.wikipedia.org/wiki/AND-OR-Invert
- https://groups.google.com/d/msg/comp.arch/fcq-GLQqvas/vTxmcA0QAgAJ
- """
-
- def __init__(self, width):
- """Create a ``MaskedFullAdder``.
-
- :param width: the bit width of the input and output
- """
- self.width = width
- self.mask = Signal(width, reset_less=True)
- self.mcarry = Signal(width, reset_less=True)
- self.in0 = Signal(width, reset_less=True)
- self.in1 = Signal(width, reset_less=True)
- self.in2 = Signal(width, reset_less=True)
- self.sum = Signal(width, reset_less=True)
-
- def elaborate(self, platform):
- """Elaborate this module."""
- m = Module()
- s1 = Signal(self.width, reset_less=True)
- s2 = Signal(self.width, reset_less=True)
- s3 = Signal(self.width, reset_less=True)
- c1 = Signal(self.width, reset_less=True)
- c2 = Signal(self.width, reset_less=True)
- c3 = Signal(self.width, reset_less=True)
- m.d.comb += self.sum.eq(self.in0 ^ self.in1 ^ self.in2)
- m.d.comb += s1.eq(Cat(0, self.in0))
- m.d.comb += s2.eq(Cat(0, self.in1))
- m.d.comb += s3.eq(Cat(0, self.in2))
- m.d.comb += c1.eq(s1 & s2 & self.mask)
- m.d.comb += c2.eq(s2 & s3 & self.mask)
- m.d.comb += c3.eq(s3 & s1 & self.mask)
- m.d.comb += self.mcarry.eq(c1 | c2 | c3)
- return m
-
-
-class PartitionedAdder(Elaboratable):
- """Partitioned Adder.
-
- Performs the final add. The partition points are included in the
- actual add (in one of the operands only), which causes a carry over
- to the next bit. Then the final output *removes* the extra bits from
- the result.
-
- partition: .... P... P... P... P... (32 bits)
- a : .... .... .... .... .... (32 bits)
- b : .... .... .... .... .... (32 bits)
- exp-a : ....P....P....P....P.... (32+4 bits, P=1 if no partition)
- exp-b : ....0....0....0....0.... (32 bits plus 4 zeros)
- exp-o : ....xN...xN...xN...xN... (32+4 bits - x to be discarded)
- o : .... N... N... N... N... (32 bits - x ignored, N is carry-over)
-
- :attribute width: the bit width of the input and output. Read-only.
- :attribute a: the first input to the adder
- :attribute b: the second input to the adder
- :attribute output: the sum output
- :attribute partition_points: the input partition points. Modification not
- supported, except for by ``Signal.eq``.
- """
-
- def __init__(self, width, partition_points, partition_step=1):
- """Create a ``PartitionedAdder``.
-
- :param width: the bit width of the input and output
- :param partition_points: the input partition points
- :param partition_step: a multiplier (typically double) step
- which in-place "expands" the partition points
- """
- self.width = width
- self.pmul = partition_step
- self.a = Signal(width, reset_less=True)
- self.b = Signal(width, reset_less=True)
- self.output = Signal(width, reset_less=True)
- self.partition_points = PartitionPoints(partition_points)
- if not self.partition_points.fits_in_width(width):
- raise ValueError("partition_points doesn't fit in width")
- expanded_width = 0
- for i in range(self.width):
- if i in self.partition_points:
- expanded_width += 1
- expanded_width += 1
- self._expanded_width = expanded_width
-
- def elaborate(self, platform):
- """Elaborate this module."""
- m = Module()
- expanded_a = Signal(self._expanded_width, reset_less=True)
- expanded_b = Signal(self._expanded_width, reset_less=True)
- expanded_o = Signal(self._expanded_width, reset_less=True)
-
- expanded_index = 0
- # store bits in a list, use Cat later. graphviz is much cleaner
- al, bl, ol, ea, eb, eo = [],[],[],[],[],[]
-
- # partition points are "breaks" (extra zeros or 1s) in what would
- # otherwise be a massive long add. when the "break" points are 0,
- # whatever is in it (in the output) is discarded. however when
- # there is a "1", it causes a roll-over carry to the *next* bit.
- # we still ignore the "break" bit in the [intermediate] output,
- # however by that time we've got the effect that we wanted: the
- # carry has been carried *over* the break point.
-
- for i in range(self.width):
- pi = i/self.pmul # double the range of the partition point test
- if pi.is_integer() and pi in self.partition_points:
- # add extra bit set to 0 + 0 for enabled partition points
- # and 1 + 0 for disabled partition points
- ea.append(expanded_a[expanded_index])
- al.append(~self.partition_points[pi]) # add extra bit in a
- eb.append(expanded_b[expanded_index])
- bl.append(C(0)) # yes, add a zero
- expanded_index += 1 # skip the extra point. NOT in the output
- ea.append(expanded_a[expanded_index])
- eb.append(expanded_b[expanded_index])
- eo.append(expanded_o[expanded_index])
- al.append(self.a[i])
- bl.append(self.b[i])
- ol.append(self.output[i])
- expanded_index += 1
-
- # combine above using Cat
- m.d.comb += Cat(*ea).eq(Cat(*al))
- m.d.comb += Cat(*eb).eq(Cat(*bl))
- m.d.comb += Cat(*ol).eq(Cat(*eo))
-
- # use only one addition to take advantage of look-ahead carry and
- # special hardware on FPGAs
- m.d.comb += expanded_o.eq(expanded_a + expanded_b)
- return m
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