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Implement double far pointer support. #8

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Implement double far pointer support. #8

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06cf1bf
Implemet double far pointer support.
Aug 19, 2015
2d539bc
Fix comments.
Aug 19, 2015
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60 changes: 45 additions & 15 deletions capnp.lua
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Original file line number Diff line number Diff line change
Expand Up @@ -391,10 +391,8 @@ function _M.read_listp(p32, header)
local sig = band(val0, 0x03)
if sig == 1 then
local offset = arshift(val0, 2)

local size_type = band(val1, 0x07)
local num = rshift(val1, 3)

return offset, size_type, num
-- return read_list_pointer(p32)
elseif sig == 2 then
Expand Down Expand Up @@ -644,28 +642,60 @@ function _M.read_listp_struct(buf, header, T, offset)
return _M.read_listp(p + base, header)
end

--- Read data structure from far pointer
-- @param buf 32-bit pointer
-- @param header stream header, see http://kentonv.github.io/capnproto/encoding.html#serialization_over_a_stream
-- @param parser function(pointer, header) parsing function for actual data structure pointer
function _M.read_far_pointer(buf, header, parser)
local p = buf
local is_double, offset, seg_id = _M.parse_far_pointer(p)
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parse_far_pointer should be a local function instead of a module function.

local far_offset = _M.get_far_offset(header, offset, seg_id)
local target_offset, target_pointer, r1, r2
if is_double == 0 then
target_pointer = _M.get_pointer_by_far_offset(header, far_offset)
target_offset, r1, r2 = parser(target_pointer, header)
else
-- According docs word after second far pointer is 'tag' describing target data structure.
-- So, we should work with it like in single-pointer case,
target_pointer = _M.get_pointer_by_far_offset(header, far_offset+1)
-- excepting offset.
_, r1, r2 = parser(target_pointer, header)
-- It should be obtained from second far pointer structure (-2 because target_pointer points to second pointer structure + 1 word).
_, target_offset, target_seg_id = _M.parse_far_pointer(target_pointer-2)
target_offset = _M.get_far_offset(header, target_offset, target_seg_id)
end
local target_offset = target_offset + (target_pointer - p) / 2
return target_offset, r1, r2
end

local landing = rshift(band(p[0], 0x04), 2)

assert(landing == 0, "double far pointer not supported yet")
--- Parse far pointer structure
-- @param p 32-bit pointer
function _M.parse_far_pointer(p)
local sig = band(p[0], 0x03)
local is_double = rshift(band(p[0], 0x04), 2)
local offset = rshift(p[0], 3)
local seg_id = tonumber(p[1])
--print("landing, offset, seg_id:", landing, offset, seg_id)
return is_double, offset, seg_id
end

-- object pointer offset
local op_offset = header.header_size
--- Get offset relative other sigments
-- @param header
-- @param offset
-- @param seg_id
function _M.get_far_offset(header, offset, seg_id)
local far_offset = header.header_size
for i=1, seg_id do
op_offset = op_offset + header.seg_sizes[i]
far_offset = far_offset + header.seg_sizes[i]
end
op_offset = op_offset + offset -- offset is in words
local pp = header.base + op_offset * 2 -- header.base is uint32_t *

local p_offset, r1, r2 = parser(pp, header)
p_offset = p_offset + (pp - p) / 2 -- p and pp are uint32_t *
return far_offset + offset
end

return p_offset, r1, r2
--- Convert offset to uint32_t * relative base
-- @param header
-- @param offset
-- @return 32-bit pointer
function _M.get_pointer_by_far_offset(header, offset)
return header.base + offset * 2
end

function _M.read_struct_buf(p32, header)
Expand Down