From fd7d3c57d7ecd75567c3c71d7deabc2c2e3b9b7f Mon Sep 17 00:00:00 2001
From: Tatsuhiro Tsujikawa <tatsuhiro.t@gmail.com>
Date: Mon, 27 Jun 2016 22:42:28 +0900
Subject: [PATCH] nghttpx: Use faster version of power

In our use case, x and y is quite small, and there is no chance for
overflow, and y is always integer.
---
 src/shrpx_connect_blocker.cc | 4 ++--
 src/shrpx_live_check.cc      | 4 ++--
 src/util.cc                  | 9 +++++++++
 src/util.h                   | 3 +++
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/shrpx_connect_blocker.cc b/src/shrpx_connect_blocker.cc
index 164dea86..4ffe29ca 100644
--- a/src/shrpx_connect_blocker.cc
+++ b/src/shrpx_connect_blocker.cc
@@ -80,8 +80,8 @@ void ConnectBlocker::on_failure() {
 
   ++fail_count_;
 
-  auto base_backoff = pow(
-      MULTIPLIER, static_cast<double>(std::min(MAX_BACKOFF_EXP, fail_count_)));
+  auto base_backoff =
+      util::int_pow(MULTIPLIER, std::min(MAX_BACKOFF_EXP, fail_count_));
   auto dist = std::uniform_real_distribution<>(-JITTER * base_backoff,
                                                JITTER * base_backoff);
 
diff --git a/src/shrpx_live_check.cc b/src/shrpx_live_check.cc
index ba0d150d..7f6559c8 100644
--- a/src/shrpx_live_check.cc
+++ b/src/shrpx_live_check.cc
@@ -157,8 +157,8 @@ constexpr auto JITTER = 0.2;
 } // namespace
 
 void LiveCheck::schedule() {
-  auto base_backoff = pow(
-      MULTIPLIER, static_cast<double>(std::min(fail_count_, MAX_BACKOFF_EXP)));
+  auto base_backoff =
+      util::int_pow(MULTIPLIER, std::min(fail_count_, MAX_BACKOFF_EXP));
   auto dist = std::uniform_real_distribution<>(-JITTER * base_backoff,
                                                JITTER * base_backoff);
 
diff --git a/src/util.cc b/src/util.cc
index 5a450bec..d24c5c8d 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1316,6 +1316,15 @@ StringRef percent_decode(BlockAllocator &balloc, const StringRef &src) {
   return StringRef{iov.base, p};
 }
 
+// Returns x**y
+double int_pow(double x, size_t y) {
+  auto res = 1.;
+  for (; y; --y) {
+    res *= x;
+  }
+  return res;
+}
+
 } // namespace util
 
 } // namespace nghttp2
diff --git a/src/util.h b/src/util.h
index 6d92529b..375dacfd 100644
--- a/src/util.h
+++ b/src/util.h
@@ -677,6 +677,9 @@ OutputIterator copy_lit(OutputIterator it, CharT(&s)[N]) {
   return std::copy_n(s, N - 1, it);
 }
 
+// Returns x**y
+double int_pow(double x, size_t y);
+
 } // namespace util
 
 } // namespace nghttp2