From ec495836450f7134069431662daf4d06e3c0bae9 Mon Sep 17 00:00:00 2001
From: Daniel Povey <dpovey@gmail.com>
Date: Thu, 10 Jun 2021 14:18:06 +0800
Subject: [PATCH]  Simplify code for getting leftover_index

---
 k2/csrc/hash.h | 30 ++++++++++--------------------
 1 file changed, 10 insertions(+), 20 deletions(-)

diff --git a/k2/csrc/hash.h b/k2/csrc/hash.h
index 4a618c83c..330c926f9 100644
--- a/k2/csrc/hash.h
+++ b/k2/csrc/hash.h
@@ -157,8 +157,7 @@ class Hash {
         uint64_t key_value = src_data[i];
         if (~key_value == 0) return;  // equals -1.. nothing there.
         uint64_t key = key_value & key_mask,
-            leftover_index = 1 |
-            ((key >> new_buckets_num_bitsm1) ^ (key & new_num_buckets_mask));
+            leftover_index = 1 | ((key >> new_buckets_num_bitsm1) ^ key);
         size_t cur_bucket = key & new_num_buckets_mask;
         while (1) {
           uint64_t assumed = ~((uint64_t)0),
@@ -286,8 +285,7 @@ class Hash {
         uint64_t *old_value = nullptr,
         uint64_t **key_value_location = nullptr) const {
       uint32_t cur_bucket = static_cast<uint32_t>(key) & num_buckets_mask_,
-          leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) & (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       constexpr int64_t KEY_MASK = (uint64_t(1)<<NUM_KEY_BITS) - 1,
           VALUE_MASK = (uint64_t(1)<< (64 - NUM_KEY_BITS)) - 1;
 
@@ -353,8 +351,7 @@ class Hash {
       constexpr int64_t KEY_MASK = (uint64_t(1) << NUM_KEY_BITS) - 1;
 
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       while (1) {
         uint64_t old_elem = data_[cur_bucket];
         if (~old_elem == 0) {
@@ -439,8 +436,7 @@ class Hash {
     __forceinline__ __host__ __device__ void Delete(uint64_t key) const {
       constexpr int64_t KEY_MASK = (uint64_t(1) << NUM_KEY_BITS) - 1;
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       while (1) {
         uint64_t old_elem = data_[cur_bucket];
         if ((old_elem & KEY_MASK) == key) {
@@ -509,8 +505,7 @@ class Hash {
         uint64_t *old_value = nullptr,
         uint64_t **key_value_location = nullptr) const {
       uint32_t cur_bucket = static_cast<uint32_t>(key) & num_buckets_mask_,
-           leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       const uint32_t num_key_bits = num_key_bits_;
       const uint64_t key_mask = (uint64_t(1) << num_key_bits) - 1,
           not_value_mask = (uint64_t(-1) << (64 - num_key_bits));
@@ -576,8 +571,7 @@ class Hash {
       const int64_t key_mask = (uint64_t(1) << num_key_bits) - 1;
 
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       while (1) {
         uint64_t old_elem = data_[cur_bucket];
         if (~old_elem == 0) {
@@ -653,8 +647,7 @@ class Hash {
     */
     __forceinline__ __host__ __device__ void Delete(uint64_t key) const {
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_));
+          leftover_index = 1 | ((key >> buckets_num_bitsm1_) ^ key);
       const uint64_t key_mask = (uint64_t(1) << num_key_bits_) - 1;
       while (1) {
         uint64_t old_elem = data_[cur_bucket];
@@ -744,8 +737,7 @@ class Hash {
       // the lowest-order `num_implicit_key_bits_` bits of the bucket index will
       // not change when we fail over to the next location.  Without this, our
       // scheme would not work.
-      uint32_t leftover_index =
-          (1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_)))
+      uint32_t leftover_index = (1 | ((key >> buckets_num_bitsm1_) ^ key))
           << num_implicit_key_bits_;
       uint64_t kept_key = key >> num_implicit_key_bits_;
 
@@ -808,8 +800,7 @@ class Hash {
       const int64_t kept_key_mask = (uint64_t(1) << num_kept_key_bits_) - 1;
 
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          (1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_)))
+          leftover_index = (1 | ((key >> buckets_num_bitsm1_) ^ key))
           << num_implicit_key_bits_;
       uint64_t kept_key = key >> num_implicit_key_bits_;
 
@@ -892,8 +883,7 @@ class Hash {
     */
     __forceinline__ __host__ __device__ void Delete(uint64_t key) const {
       uint32_t cur_bucket = key & num_buckets_mask_,
-          leftover_index =
-          (1 | ((key >> buckets_num_bitsm1_) ^ (key & num_buckets_mask_)))
+          leftover_index = (1 | ((key >> buckets_num_bitsm1_) ^ key))
           << num_implicit_key_bits_;
       uint64_t kept_key = key >> num_implicit_key_bits_;
       const uint64_t kept_key_mask = (uint64_t(1) << num_kept_key_bits_) - 1;