48 lines
1.9 KiB
Nim
48 lines
1.9 KiB
Nim
type
|
|
BitField* = object
|
|
## A simple bit field type that follows the semantics of the spec, with
|
|
## regards to bit endian operations
|
|
# TODO nim-ranges contains utilities for with bitsets - could try to
|
|
# recycle that, but there are open questions about bit endianess there.
|
|
# TODO define a json serialization.. together with spec tests?
|
|
# https://github.com/ethereum/eth2.0-tests/tree/master/state
|
|
bits*: seq[byte]
|
|
|
|
func ceil_div8(v: int): int = (v + 7) div 8
|
|
|
|
func init*(T: type BitField, bits: int): BitField =
|
|
BitField(bits: newSeq[byte](ceil_div8(bits)))
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#get_bitfield_bit
|
|
func get_bitfield_bit*(bitfield: BitField, i: int): bool =
|
|
# Extract the bit in ``bitfield`` at position ``i``.
|
|
doAssert 0 <= i div 8, "i: " & $i & " i div 8: " & $(i div 8)
|
|
doAssert i div 8 < bitfield.bits.len, "i: " & $i & " i div 8: " & $(i div 8)
|
|
((bitfield.bits[i div 8] shr (i mod 8)) mod 2) > 0'u8
|
|
|
|
# https://github.com/ethereum/eth2.0-specs/blob/v0.5.0/specs/core/0_beacon-chain.md#verify_bitfield
|
|
func verify_bitfield*(bitfield: BitField, committee_size: int): bool =
|
|
# Verify ``bitfield`` against the ``committee_size``.
|
|
if len(bitfield.bits) != (committee_size + 7) div 8:
|
|
return false
|
|
|
|
# Check `bitfield` is padded with zero bits only
|
|
for i in committee_size ..< (len(bitfield.bits) * 8):
|
|
if get_bitfield_bit(bitfield, i):
|
|
return false
|
|
|
|
true
|
|
|
|
# TODO spec candidatidates below, though they're used only indirectly there..
|
|
func set_bitfield_bit*(bitfield: var BitField, i: int) =
|
|
bitfield.bits[i div 8] = bitfield.bits[i div 8] or 1'u8 shl (i mod 8)
|
|
|
|
func combine*(tgt: var BitField, src: BitField) =
|
|
for i in 0 ..< tgt.bits.len:
|
|
tgt.bits[i] = tgt.bits[i] or src.bits[i]
|
|
|
|
proc overlaps*(a, b: BitField): bool =
|
|
for i in 0..<a.bits.len:
|
|
if (a.bits[i] and b.bits[i]) > 0'u8:
|
|
return true
|