From 48531785b74d2f6728282937a105595467b94cc7 Mon Sep 17 00:00:00 2001
From: Jeffrey Walton <noloader@gmail.com>
Date: Tue, 5 Feb 2019 02:05:36 -0500
Subject: [PATCH] Use IsPowerOf2 in Integer::Divide

---
 integer.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/integer.cpp b/integer.cpp
index 1771b429b..78dd10a10 100644
--- a/integer.cpp
+++ b/integer.cpp
@@ -4244,7 +4244,9 @@ void Integer::Divide(word &remainder, Integer &quotient, const Integer &dividend
 	if (!divisor)
 		throw Integer::DivideByZero();
 
-	if ((divisor & (divisor-1)) == 0)	// divisor is a power of 2
+	// IsPowerOf2 uses BMI on x86 if available. There is a small
+	// but measurable improvement during decryption and signing.
+	if (IsPowerOf2(divisor))
 	{
 		quotient = dividend >> (BitPrecision(divisor)-1);
 		remainder = dividend.reg[0] & (divisor-1);