Minor optimizations in BigInt memory handling

Makes 4-6% difference for ECDSA

2 files changed, 4 insertions, 2 deletions

diff --git a/src/lib/math/bigint/big_ops2.cpp b/src/lib/math/bigint/big_ops2.cpp
index c203f363a..639d87ceb 100644
--- a/src/lib/math/bigint/big_ops2.cpp
+++ b/src/lib/math/bigint/big_ops2.cpp
@@ -21,7 +21,9 @@ BigInt& BigInt::operator+=(const BigInt& y)
    const size_t x_sw = sig_words(), y_sw = y.sig_words();
 
    const size_t reg_size = std::max(x_sw, y_sw) + 1;
-   grow_to(reg_size);
+
+   if(m_reg.size() < reg_size)
+      grow_to(reg_size);
 
    if(sign() == y.sign())
       bigint_add2(mutable_data(), reg_size - 1, y.data(), y_sw);
diff --git a/src/lib/math/bigint/bigint.cpp b/src/lib/math/bigint/bigint.cpp
index b63bd9be8..e5f8974d5 100644
--- a/src/lib/math/bigint/bigint.cpp
+++ b/src/lib/math/bigint/bigint.cpp
@@ -23,7 +23,7 @@ BigInt::BigInt(uint64_t n)
 
    const size_t limbs_needed = sizeof(uint64_t) / sizeof(word);
 
-   m_reg.resize(4*limbs_needed);
+   m_reg.resize(limbs_needed);
    for(size_t i = 0; i != limbs_needed; ++i)
       m_reg[i] = ((n >> (i*MP_WORD_BITS)) & MP_WORD_MASK);
    }