def test_new_far():
p = ptr.new_far(0, 725, 1)
assert ptr.kind(p) == ptr.FAR
assert ptr.far_landing_pad(p) == 0
assert ptr.far_offset(p) == 725
assert ptr.far_target(p) == 1
assert p == 0x00000001000016aa
def test_FarPtr():
# 00000001 target
# 000016aa offset
# a landing
# a kind
p = 0x00000001000016aa
assert ptr.kind(p) == ptr.FAR
assert ptr.far_landing_pad(p) == 0
assert ptr.far_offset(p) == 725
assert ptr.far_target(p) == 1
def read_far_ptr(self, offset):
"""
Read and return the ptr referenced by this far pointer
"""
p = self.read_ptr(offset)
assert ptr.far_landing_pad(p) == 0
segment_start = self.segment_offsets[ptr.far_target(p)] # in bytes
offset = segment_start + ptr.far_offset(p) * 8
p = self.read_ptr(offset)
return offset, p
def read_far_ptr(self, offset):
"""
Read and return the ptr referenced by this far pointer
"""
p = self.read_ptr(offset)
segment_start = self.segment_offsets[ptr.far_target(p)] # in bytes
offset = segment_start + ptr.far_offset(p) * 8
if ptr.far_landing_pad(p) == 0:
# simple case: the landing pad is a normal pointer, just read it
p = self.read_ptr(offset)
return offset, p
else:
# complex case. From capnproto specs:
# If B == 1, then the "landing pad" is itself another far
# pointer that is interpreted differently: This far pointer
# (which always has B = 0) points to the start of the object's
# content, located in some other segment. The landing pad is
# itself immediately followed by a tag word. The tag word
# looks exactly like an intra-segment pointer to the target
# object would look, except that the offset is always zero.
#
# read the 2nd far pointer and the tag word
p = self.read_ptr(offset)
ptag = self.read_ptr(offset + 8)
assert ptr.kind(p) == ptr.FAR
assert ptr.far_landing_pad(p) == 0
assert ptr.offset(ptag) == 0
# compute the absolute offset which the object is located at
segment_start = self.segment_offsets[ptr.far_target(p)] # in bytes
offset = segment_start + ptr.far_offset(p) * 8
#
# ptag is a pointer which perfectly describes the object we want
# to read. Remember that normally when ptr_offset==0, capnproto
# expects the object to start at offset+8. So here we return
# offset-8, so that the object will be read at the expected place
return offset - 8, ptag
def unpack(p):
assert ptr.kind(p) == ptr.FAR
return ptr.far_landing_pad(p), ptr.far_offset(p), ptr.far_target(p)
