2 files changed, 121 insertions, 0 deletions
diff --git a/io/init.lua b/io/init.lua
index 4a663a7..9bbd51a 100644
--- a/io/init.lua
+++ b/io/init.lua
@@ -28,3 +28,25 @@ function nerv.ChunkFile:read_chunk(id, global_conf)
     chunk:read(self:get_chunkdata(id))
     return chunk
 end
+
+local DataReader = nerv.class("nerv.DataReader")
+
+function DataReader:__init(global_conf, reader_conf)
+    nerv.error_method_not_implemented()
+end
+
+function DataReader:get_data()
+    nerv.error_method_not_implemented()
+end
+
+local DataBuffer = nerv.class("nerv.DataBuffer")
+
+function DataBuffer:__init(global_conf, buffer_conf)
+    nerv.error_method_not_implemented()
+end
+
+function DataBuffer:get_batch()
+    nerv.error_method_not_implemented()
+end
+
+require 'io.sgd_buffer'
diff --git a/io/sgd_buffer.lua b/io/sgd_buffer.lua
new file mode 100644
index 0000000..dadcf67
--- /dev/null
+++ b/io/sgd_buffer.lua
@@ -0,0 +1,99 @@
+local SGDBuffer = nerv.class("nerv.SGDBuffer", "nerv.DataBuffer")
+
+function SGDBuffer:__init(global_conf, buffer_conf)
+    self.gconf = global_conf
+    self.buffer_size = math.floor(buffer_conf.buffer_size /
+                                global_conf.batch_size) * global_conf.batch_size
+    self.head = 0
+    self.tail = 0
+    self.readers = {}
+    for i, reader_spec in ipairs(buffer_conf.readers) do
+        local buffs = {}
+        for id, width in pairs(reader_spec.data) do
+            buffs[id] = {data = global_conf.mmat_type(self.buffer_size, width),
+                        leftover = {},
+                        width = width}
+        end
+        table.insert(self.readers, {buffs = buffs,
+                                    reader = reader_spec.reader,
+                                    tail = 0,
+                                    has_leftover = false})
+    end
+end
+
+function SGDBuffer:saturate()
+    local buffer_size = self.buffer_size
+    self.head = 0
+    self.tail = buffer_size
+    for i, reader in ipairs(self.readers) do
+        reader.tail = 0
+        if reader.has_leftover then
+            local lrow
+            for id, buff in pairs(reader.buffs) do
+                lrow = buff.leftover:nrow()
+                if lrow > buffer_size then
+                    nerv.error("buffer size is too small to contain leftovers")
+                end
+                buff.data:copy_from(buff.leftover, 0, lrow)
+            end
+            reader.tail = lrow
+            reader.has_leftover = false
+        end
+        while reader.tail < buffer_size do
+            local data = reader.reader:get_data()
+            if data == nil then
+                break
+            end
+            local drow = nil
+            for id, d in pairs(data) do
+                if drow == nil then
+                    drow = d:nrow()
+                elseif d:nrow() ~= drow then
+                    nerv.error("reader provides with inconsistent rows of data")
+                end
+            end
+            local remain = buffer_size - reader.tail
+            if drow > remain then
+                for id, buff in pairs(reader.buffs) do
+                    local d = data[id]
+                    if d == nil then
+                        nerv.error("reader does not provide data for %s", id)
+                    end
+                    buff.leftover = self.gconf.mmat_type(drow - remain,
+                                                        buff.width)
+                    buff.leftover:copy_from(d, remain, drow)
+                end
+                drow = remain
+                reader.has_leftover = true
+            end
+            for id, buff in pairs(reader.buffs) do
+                buff.data:copy_from(data[id], 0, drow, reader.tail)
+            end
+            reader.tail = reader.tail + drow
+        end
+        self.tail = math.min(self.tail, reader.tail)
+    end
+    return self.tail >= self.gconf.batch_size
+end
+
+function SGDBuffer:get_data()
+    local batch_size = self.gconf.batch_size
+    if self.head >= self.tail then -- buffer is empty
+        if not self:saturate() then
+            return nil -- the remaining data cannot build a batch
+        end
+    end
+    if self.head + batch_size > self.tail then
+        return nil -- the remaining data cannot build a batch
+    end
+    local res = {}
+    for i, reader in ipairs(self.readers) do
+        for id, buff in pairs(reader.buffs) do
+            local batch = self.gconf.cumat_type(batch_size, buff.width)
+            batch:copy_fromh(buff.data, self.head, self.head + batch_size)
+            res[id] = batch
+        end
+    end
+    self.head = self.head + batch_size
+    return res
+end