From 7d9c36aae12e4ea5aad7ce7a28e94dc94c9d3c00 Mon Sep 17 00:00:00 2001
From: tangxifan <tangxifan@gmail.com>
Date: Fri, 3 Jul 2020 12:06:15 -0600
Subject: [PATCH] use length instead of msb in bitstream manager for block bits
 to save memory

---
 .../src/bitstream_manager.cpp                 | 22 ++++++++++---------
 .../libfpgabitstream/src/bitstream_manager.h  |  2 +-
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
index b2d894427..d8622617d 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.cpp
@@ -78,11 +78,15 @@ std::vector<ConfigBitId> BitstreamManager::block_bits(const ConfigBlockId& block
   VTR_ASSERT(true == valid_block_id(block_id));
 
   size_t lsb = block_bit_id_lsbs_[block_id]; 
-  size_t msb = block_bit_id_msbs_[block_id]; 
+  size_t length = block_bit_lengths_[block_id]; 
 
-  std::vector<ConfigBitId> bits(msb - lsb + 1, ConfigBitId::INVALID());
+  std::vector<ConfigBitId> bits(length, ConfigBitId::INVALID());
 
-  for (size_t i = lsb; i < msb + 1; ++i) {
+  if (0 == length) {
+    return bits;
+  }
+
+  for (size_t i = lsb; i < lsb + length; ++i) {
     bits[i - lsb] = ConfigBitId(i);
   }
 
@@ -152,7 +156,7 @@ ConfigBitId BitstreamManager::add_bit(const bool& bit_value) {
 void BitstreamManager::reserve_blocks(const size_t& num_blocks) {
   block_names_.reserve(num_blocks);
   block_bit_id_lsbs_.reserve(num_blocks);
-  block_bit_id_msbs_.reserve(num_blocks);
+  block_bit_lengths_.reserve(num_blocks);
   block_path_ids_.reserve(num_blocks);
   block_input_net_ids_.reserve(num_blocks);
   block_output_net_ids_.reserve(num_blocks);
@@ -169,8 +173,8 @@ ConfigBlockId BitstreamManager::create_block() {
   /* Add a new bit, and allocate associated data structures */
   num_blocks_++;
   block_names_.emplace_back();
-  block_bit_id_lsbs_.emplace_back(0);
-  block_bit_id_msbs_.emplace_back(-1);
+  block_bit_id_lsbs_.emplace_back(-1);
+  block_bit_lengths_.emplace_back(0);
   block_path_ids_.push_back(-2);
   block_input_net_ids_.emplace_back();
   block_output_net_ids_.emplace_back();
@@ -218,13 +222,11 @@ void BitstreamManager::add_block_bits(const ConfigBlockId& block,
   VTR_ASSERT(true == valid_block_id(block));
 
   /* Add the bit to the block, record anchors in bit indexing for block-level searching */
-  size_t lsb = num_bits_;
-  size_t msb = num_bits_ + block_bitstream.size() - 1;
+  block_bit_id_lsbs_[block] = num_bits_;
+  block_bit_lengths_[block] = block_bitstream.size();
   for (const bool& bit : block_bitstream) {
     add_bit(bit);
   }
-  block_bit_id_lsbs_[block] = lsb;
-  block_bit_id_msbs_[block] = msb;
 }
 
 void BitstreamManager::add_path_id_to_block(const ConfigBlockId& block, const int& path_id) {
diff --git a/libopenfpga/libfpgabitstream/src/bitstream_manager.h b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
index dd724fac9..fbc5d39c3 100644
--- a/libopenfpga/libfpgabitstream/src/bitstream_manager.h
+++ b/libopenfpga/libfpgabitstream/src/bitstream_manager.h
@@ -197,7 +197,7 @@ class BitstreamManager {
     size_t num_blocks_; 
     std::unordered_set<ConfigBlockId> invalid_block_ids_;
     vtr::vector<ConfigBlockId, size_t> block_bit_id_lsbs_; 
-    vtr::vector<ConfigBlockId, size_t> block_bit_id_msbs_; 
+    vtr::vector<ConfigBlockId, short> block_bit_lengths_; 
 
     /* Back-annotation for the bits */
     /* Parent block of a bit in the Bitstream