diff --git a/6502.lua b/6502.lua
index 730509a..e12e50e 100644
--- a/6502.lua
+++ b/6502.lua
@@ -1,5 +1,9 @@
local M = {}
+local symbols = {}
+local sections = {}
+local locations = {}
+
local byte_normalize = function(v)
if v < -128 or v > 255 then error("value out of byte range: " .. v) end
if v < 0 then v = v + 0x100 end
@@ -21,6 +25,126 @@ local word_emit = function(v, bin)
bin[#bin+1] = 0xff & (v // 0x100)
end
+local link = function()
+ for _,location in ipairs(locations) do
+
+ local chunk_reserve = function(chunk_ix, chunk, start, size)
+ if start == chunk.start then
+ if size == chunk.size then location.chunks[chunk_ix] = nil
+ else chunk.start=start+size chunk.size=chunk.size-size end
+ else
+ if chunk.size - (start - chunk.start) == size then chunk.size = chunk.size - size
+ else
+ chunk.size = start - chunk.start
+ table.insert(location.chunks, chunk_ix+1, { start=start+size, size=chunk.start+chunk.size-(start+size) })
+ end
+ end
+ end
+
+ -- filter sections list
+ local position_independent_sections = {}
+ local symbols_to_remove = {}
+ for ix,section in ipairs(sections) do
+ if symbols[section.label] then error("duplicate symbol: " .. section.label) end
+ symbols[section.label] = section
+ section:compute_size()
+ if section.size == 0 then
+ sections[ix]=nil
+ if not section.org then table.insert(symbols_to_remove, section.label) end
+ elseif not section.org then table.insert(position_independent_sections, section) end
+ end
+ for _,v in ipairs(symbols_to_remove) do symbols[v] = nil end
+
+ -- fixed position sections
+ for section_ix,section in ipairs(sections) do if section.org then
+ if section.org < location.start or section.org > location.finish then
+ error("ORG section " .. section.label .. " starts outside container location")
+ end
+ for chunk_ix,chunk in ipairs(location.chunks) do
+ if chunk.start <= section.org and chunk.size - (section.org - chunk.start) >= section.size then
+ chunk_reserve(chunk_ix, chunk, section.org, section.size)
+ goto chunk_located
+ end
+ end
+ error("ORG section " .. section.label .. " overflows its location")
+ ::chunk_located::
+ end end
+
+ -- position independent sections
+ table.sort(position_independent_sections, function(a,b) return a.size < b.size end)
+ while #position_independent_sections > 0 do
+ local section = position_independent_sections[1]
+ local chunks = {}
+ for _,chunk in ipairs(location.chunks) do
+ if chunk.size >= section.size then chunks[#chunks+1] = chunk end
+ end
+ table.sort(chunks, function(a,b) return a.size < b.size end)
+ for chunk_ix,chunk in ipairs(chunks) do
+ local waste,position = math.maxinteger
+ local usage_lowest = function(start, finish)
+ local inc=1
+ if section.align then
+ start = (start + section.align - 1) // section.align * section.align
+ if section.offset then start = start + section.offset end
+ inc = section.align
+ end
+ for address=start,finish,inc do
+ for _,constraint in ipairs(section.constraints) do
+ local start, finish = address+contraint.start, address+constraint.finish
+ if start // 0x100 == finish // 0x100 then
+ if constraint.type == 'crosspage' then goto constraints_not_met end
+ else
+ if constraint.type == 'samepage' then goto constraints_not_met end
+ end
+ end
+ local w = math.min(address - chunk.start, chunk.size - (address - chunk.start))
+ if w < waste then waste=w position=address end
+ ::constraints_not_met::
+ end
+ end
+ local finish = math.min(chunk.start + 0xff, chunk.start + chunk.size - section.size)
+ usage_lowest(chunk.start, finish)
+ if chunk.size ~= math.huge then
+ local start = math.max(chunk.start + chunk.size - section.size - 0xff, chunk.start)
+ usage_lowest(start, chunk.start + chunk.size - section.size)
+ end
+ if position then
+ chunk_reserve(chunk_ix, chunk, position, section.size)
+ section.org = position
+ goto chunk_located
+ end
+ end
+ error("unable to find space for section " .. section.label)
+ ::chunk_located::
+ end
+
+ end
+end
+
+M.location = function(start, finish)
+ local size = (finish or math.huge) - start
+ locations[#locations+1] = { start=start, finish=finish, chunks={ { start=start, size=size } } }
+end
+
+M.section = function(t)
+ local section = {}
+ if (type(t) == 'string') then section.label = t
+ else
+ assert(type(t) == 'table')
+ assert(type(t[1]) == 'string' and string.len(t[1]) > 0)
+ section=t section.label=t[1] section[1]=nil
+ if section.offset and not section.align then error("section " .. section.label .. " has offset, but no align") end
+ end
+ section.constraints = {}
+ section.instructions = {}
+ function section:compute_size()
+ self.size = 0
+ for _,instruction in ipairs(self.instructions) do
+ -- TODO
+ end
+ end
+end
+
M.byte = function(...)
local data = {...}
for _,v in ipairs(data) do byte_emit(byte_normalize(v)) end
@@ -30,17 +154,6 @@ M.word = function(...)
for _,v in ipairs(data) do word_emit(word_normalize(v)) end
end
-M.section = function(t)
- local s = {}
- if (type(t) == 'string') then s.name = t
- else
- assert(type(t) == 'table')
- assert(type(t.name) == 'string' and string.len(t.name) > 0)
- s = t
- end
- s.instructions = {}
-end
-
return M
--[===[