From ac1d24cf06de5e800cbb8a3c7ab392c081aeb783 Mon Sep 17 00:00:00 2001
From: Jack Lloyd <jack@randombit.net>
Date: Mon, 26 Feb 2018 07:56:20 -0500
Subject: Add BigInt::operator*= taking a word

Avoids memory allocation when multiplying by a small constant.
---
 src/lib/math/bigint/big_ops2.cpp | 19 +++++++++++++++++--
 src/lib/math/bigint/bigint.h     |  6 ++++++
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/src/lib/math/bigint/big_ops2.cpp b/src/lib/math/bigint/big_ops2.cpp
index 2f81989c3..7653884c9 100644
--- a/src/lib/math/bigint/big_ops2.cpp
+++ b/src/lib/math/bigint/big_ops2.cpp
@@ -107,12 +107,12 @@ BigInt& BigInt::operator*=(const BigInt& y)
       }
    else if(x_sw == 1 && y_sw)
       {
-      grow_to(y_sw + 2);
+      grow_to(y_sw + 1);
       bigint_linmul3(mutable_data(), y.data(), y_sw, word_at(0));
       }
    else if(y_sw == 1 && x_sw)
       {
-      grow_to(x_sw + 2);
+      grow_to(x_sw + 1);
       bigint_linmul2(mutable_data(), x_sw, y.word_at(0));
       }
    else
@@ -125,6 +125,21 @@ BigInt& BigInt::operator*=(const BigInt& y)
    return (*this);
    }
 
+BigInt& BigInt::operator*=(word y)
+   {
+   if(y == 0)
+      {
+      clear();
+      set_sign(Positive);
+      }
+
+   const size_t x_sw = sig_words();
+   grow_to(x_sw + 1);
+   bigint_linmul2(mutable_data(), x_sw, y);
+
+   return (*this);
+   }
+
 /*
 * Division Operator
 */
diff --git a/src/lib/math/bigint/bigint.h b/src/lib/math/bigint/bigint.h
index 71629b3aa..2c1d5e905 100644
--- a/src/lib/math/bigint/bigint.h
+++ b/src/lib/math/bigint/bigint.h
@@ -153,6 +153,12 @@ class BOTAN_PUBLIC_API(2,0) BigInt final
      */
      BigInt& operator*=(const BigInt& y);
 
+     /**
+     * *= operator
+     * @param y the word to multiply with this
+     */
+     BigInt& operator*=(word y);
+
      /**
      * /= operator
      * @param y the BigInt to divide this by
-- 
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