From 190eb95f226e4efd4f0b25b5d35f7ad9ed9a3939 Mon Sep 17 00:00:00 2001
From: Kevin Pan <zhibiao.pan@bitmain.com>
Date: Thu, 5 Jan 2017 10:03:19 +0800
Subject: [PATCH 1/2] improve format diff, O(n^2) -> O(n)

---
 src/Common.h          | 17 +++++++++++++++++
 src/StratumSession.cc | 26 ++++----------------------
 test/TestCommon.cc    | 13 +++++++++++++
 3 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/src/Common.h b/src/Common.h
index b59ae0c4c..bac111b55 100644
--- a/src/Common.h
+++ b/src/Common.h
@@ -151,4 +151,21 @@ inline void BitsToDifficulty(uint32 bits, uint64 *difficulty) {
   *difficulty = (uint64)diff;
 }
 
+// diff must be 2^N
+inline uint64_t formatDifficulty(const uint64_t diff) {
+  // set UINT64_MAX/2 as maximum difficulty
+  if (diff >= UINT64_MAX / 2) {
+    return UINT64_MAX / 2;
+  }
+
+  uint64_t newDiff = 1;
+  int i = 0;
+  while (newDiff < diff) {
+    newDiff = newDiff << 1;
+    i++;
+  }
+  assert(i <= 63);
+  return 1ULL << i;
+}
+
 #endif
diff --git a/src/StratumSession.cc b/src/StratumSession.cc
index 9d9de0aa8..2986fe0c2 100644
--- a/src/StratumSession.cc
+++ b/src/StratumSession.cc
@@ -480,27 +480,16 @@ void StratumSession::_handleRequest_AuthorizePassword(const string &password) {
     }
   }
 
+  d  = formatDifficulty(d);
+  md = formatDifficulty(md);
+
   // set min diff first
   if (md >= DiffController::kMinDiff_) {
-    // diff must be 2^N
-    double i = 1;
-    while ((uint64_t)exp2(i) < md) {
-      i++;
-    }
-    md = (uint64_t)exp2(i);
-
     diffController_.setMinDiff(md);
   }
 
   // than set current diff
   if (d >= DiffController::kMinDiff_) {
-    // diff must be 2^N
-    double i = 1;
-    while ((uint64_t)exp2(i) < d) {
-      i++;
-    }
-    d = (uint64_t)exp2(i);
-
     diffController_.resetCurDiff(d);
   }
 }
@@ -584,14 +573,7 @@ void StratumSession::handleExMessage_AuthorizeAgentWorker(const int64_t workerId
 }
 
 void StratumSession::_handleRequest_SetDifficulty(uint64_t suggestDiff) {
-  // suggestDiff must be 2^N
-  double i = 1;
-  while ((uint64_t)exp2(i) < suggestDiff) {
-    i++;
-  }
-  suggestDiff = (uint64_t)exp2(i);
-
-  diffController_.resetCurDiff(suggestDiff);
+  diffController_.resetCurDiff(formatDifficulty(suggestDiff));
 }
 
 void StratumSession::handleRequest_SuggestTarget(const string &idStr,
diff --git a/test/TestCommon.cc b/test/TestCommon.cc
index 64e551004..c1b160b0b 100644
--- a/test/TestCommon.cc
+++ b/test/TestCommon.cc
@@ -284,3 +284,16 @@ TEST(Common, BitsToDifficulty) {
   ASSERT_EQ((uint64_t)(d * 10000.0), 163074209ull);
 }
 
+TEST(Common, formatDifficulty) {
+  ASSERT_EQ(formatDifficulty(UINT64_MAX),   UINT64_MAX/2);
+  ASSERT_EQ(formatDifficulty(UINT64_MAX/2), UINT64_MAX/2);
+
+  // 2^32 = UINT32_MAX + 1
+  ASSERT_EQ(formatDifficulty(UINT32_MAX),               (uint64_t)UINT32_MAX + 1);
+  ASSERT_EQ(formatDifficulty((uint64_t)UINT32_MAX + 1), (uint64_t)UINT32_MAX + 1);
+
+  ASSERT_EQ(formatDifficulty(0), 1);
+  ASSERT_EQ(formatDifficulty(1), 1);
+  ASSERT_EQ(formatDifficulty(2), 2);
+  ASSERT_EQ(formatDifficulty(3), 4);
+}

From e13ab5bad668afcff0947b3fb186104498b27803 Mon Sep 17 00:00:00 2001
From: Kevin Pan <zhibiao.pan@bitmain.com>
Date: Thu, 5 Jan 2017 10:49:37 +0800
Subject: [PATCH 2/2] fixed: UINT64_MAX / 2 is not equal to 2^63

---
 src/Common.h       | 7 ++++---
 test/TestCommon.cc | 3 +--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/Common.h b/src/Common.h
index bac111b55..dd88c3340 100644
--- a/src/Common.h
+++ b/src/Common.h
@@ -153,9 +153,10 @@ inline void BitsToDifficulty(uint32 bits, uint64 *difficulty) {
 
 // diff must be 2^N
 inline uint64_t formatDifficulty(const uint64_t diff) {
-  // set UINT64_MAX/2 as maximum difficulty
-  if (diff >= UINT64_MAX / 2) {
-    return UINT64_MAX / 2;
+  // set 2^63 as maximum difficulty, 2^63 = 9223372036854775808
+  const uint64_t kMaxDiff = 9223372036854775808ull;
+  if (diff >= kMaxDiff) {
+    return kMaxDiff;
   }
 
   uint64_t newDiff = 1;
diff --git a/test/TestCommon.cc b/test/TestCommon.cc
index c1b160b0b..9e39ba009 100644
--- a/test/TestCommon.cc
+++ b/test/TestCommon.cc
@@ -285,8 +285,7 @@ TEST(Common, BitsToDifficulty) {
 }
 
 TEST(Common, formatDifficulty) {
-  ASSERT_EQ(formatDifficulty(UINT64_MAX),   UINT64_MAX/2);
-  ASSERT_EQ(formatDifficulty(UINT64_MAX/2), UINT64_MAX/2);
+  ASSERT_EQ(formatDifficulty(UINT64_MAX), 9223372036854775808ull);
 
   // 2^32 = UINT32_MAX + 1
   ASSERT_EQ(formatDifficulty(UINT32_MAX),               (uint64_t)UINT32_MAX + 1);