From e829ef9253dfece9ff9f599130bc625f1267e136 Mon Sep 17 00:00:00 2001
From: txh18 <cloudygooseg@gmail.com>
Date: Wed, 20 Jan 2016 15:15:28 +0800
Subject: used prefixsum_row operation to speed up sampling on the softmax
 output

---
 nerv/examples/lmptb/lm_sampler.lua            | 35 +++++++++++++++++++++++----
 nerv/examples/lmptb/sample_grulm_ptb_main.lua |  4 +--
 2 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/nerv/examples/lmptb/lm_sampler.lua b/nerv/examples/lmptb/lm_sampler.lua
index c25a75c..2a4f1c3 100644
--- a/nerv/examples/lmptb/lm_sampler.lua
+++ b/nerv/examples/lmptb/lm_sampler.lua
@@ -27,7 +27,8 @@ function LMSampler:load_dagL(dagL)
     self.dagL_outputs[2] = global_conf.cumat_type(global_conf.batch_size, global_conf.hidden_size)
     
     self.smout_d = global_conf.cumat_type(self.batch_size, self.vocab:size())
-    self.smout_h = global_conf.mmat_type(self.batch_size, self.vocab:size())
+    self.ssout_d = global_conf.cumat_type(self.batch_size, self.vocab:size())
+    self.ssout_h = global_conf.mmat_type(self.batch_size, self.vocab:size())
 
     self.store = {}
     for i = 1, self.batch_size do
@@ -40,9 +41,27 @@ function LMSampler:load_dagL(dagL)
     self.repo = {}
 end
 
-function LMSampler:sample_to_store(smout)
+function LMSampler:sample_to_store(ssout)
     for i = 1, self.batch_size do
         local ran = math.random()
+        local id = 1
+        local low = 0
+        local high = ssout:ncol() - 1
+        if ssout[i - 1][high] < 0.9999 or ssout[i - 1][high] > 1.0001 then
+            nerv.error("%s ERROR, softmax output summation(%f) seems to have some problem", self.log_pre, ssout[i - 1][high])
+        end
+        if ssout[i - 1][low] < ran then
+            while low + 1 < high do
+                local mid = math.floor((low + high) / 2)
+                if ssout[i - 1][mid] < ran then
+                    low = mid
+                else
+                    high = mid
+                end
+            end
+            id = high + 1
+        end
+        --[[
         local s = 0
         local id = self.vocab:size()
         for j = 0, self.vocab:size() - 1 do
@@ -52,13 +71,18 @@ function LMSampler:sample_to_store(smout)
                 break
             end
         end
+        ]]--
         if #self.store[i] >= self.chunk_size - 2 then
             id = self.sen_end_id
         end
         local tmp = {}
         tmp.w = self.vocab:get_word_id(id).str
         tmp.id = id
-        tmp.p = smout[i - 1][id - 1]
+        if id == 1 then
+            tmp.p = ssout[i - 1][id - 1]
+        else
+            tmp.p = ssout[i - 1][id - 1] - ssout[i - 1][id - 2] 
+        end
         table.insert(self.store[i], tmp)
     end
 end
@@ -74,9 +98,10 @@ function LMSampler:lm_sample_rnn_dagL(sample_num, p_conf)
         inputs[2]:copy_fromd(outputs[2]) --copy hidden activation
     
         self.smout_d:softmax(outputs[1])
-        self.smout_d:copy_toh(self.smout_h)
+        self.ssout_d:prefixsum_row(self.smout_d)
+        self.ssout_d:copy_toh(self.ssout_h)
         
-        self:sample_to_store(self.smout_h)
+        self:sample_to_store(self.ssout_h)
         for i = 1, self.batch_size do
             inputs[1][i - 1][0] = self.store[i][#self.store[i]].id - 1
             if self.store[i][#self.store[i]].id == self.sen_end_id then --meet a sentence end
diff --git a/nerv/examples/lmptb/sample_grulm_ptb_main.lua b/nerv/examples/lmptb/sample_grulm_ptb_main.lua
index 9a13d36..30dfe26 100644
--- a/nerv/examples/lmptb/sample_grulm_ptb_main.lua
+++ b/nerv/examples/lmptb/sample_grulm_ptb_main.lua
@@ -424,11 +424,11 @@ if commands["sampling"] == 1 then
     local dagL = load_net_dagL(global_conf, global_conf.fn_to_sample) 
     local sampler = nerv.LMSampler(global_conf)
     sampler:load_dagL(dagL)
-    for k = 1, 5 do
+    for k = 1, 1 do
         local res = sampler:lm_sample_rnn_dagL(10, {})
         for i = 1, #res do
             for j = 1, #res[i] do
-                nerv.printf("%s ", res[i][j].w)
+                nerv.printf("%s(%f) ", res[i][j].w, res[i][j].p)
             end
             nerv.printf("\n")
         end
-- 
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