Use resize instead of shrink_to_fit

Avoid recalculating significant words which slows down reduction

2 files changed, 10 insertions, 3 deletions

diff --git a/src/lib/math/bigint/bigint.h b/src/lib/math/bigint/bigint.h
index 530fd5ecf..bd63425fd 100644
--- a/src/lib/math/bigint/bigint.h
+++ b/src/lib/math/bigint/bigint.h
@@ -570,6 +570,8 @@ class BOTAN_PUBLIC_API(2,0) BigInt final
         m_data.shrink_to_fit(min_size);
         }
 
+     void resize(size_t s) { m_data.resize(s); }
+
      /**
      * Fill BigInt with a random number with size of bitsize
      *
@@ -910,6 +912,11 @@ class BOTAN_PUBLIC_API(2,0) BigInt final
               m_reg.resize(words);
               }
 
+           void resize(size_t s)
+              {
+              m_reg.resize(s);
+              }
+
            void swap(Data& other)
               {
               m_reg.swap(other.m_reg);
diff --git a/src/lib/math/numbertheory/nistp_redc.cpp b/src/lib/math/numbertheory/nistp_redc.cpp
index abec38d75..5ad4515b4 100644
--- a/src/lib/math/numbertheory/nistp_redc.cpp
+++ b/src/lib/math/numbertheory/nistp_redc.cpp
@@ -247,7 +247,7 @@ void redc_p224(BigInt& x, secure_vector<word>& ws)
    const int64_t S6 = 0xFFFFFFFF + X06 + X10 - X13;
 
    x.mask_bits(224);
-   x.shrink_to_fit(p224_limbs + 1);
+   x.resize(p224_limbs + 1);
 
    int64_t S = 0;
    uint32_t R0 = 0, R1 = 0;
@@ -358,7 +358,7 @@ void redc_p256(BigInt& x, secure_vector<word>& ws)
    const int64_t S7 = 0xFFFFFFFA + X07 + X15*3 + X08 - X10 - X11 - X12 - X13;
 
    x.mask_bits(256);
-   x.shrink_to_fit(p256_limbs + 1);
+   x.resize(p256_limbs + 1);
 
    int64_t S = 0;
 
@@ -505,7 +505,7 @@ void redc_p384(BigInt& x, secure_vector<word>& ws)
    const int64_t SB = 0xFFFFFFFF + X11 + X19 + X20 + X23 - X22;
 
    x.mask_bits(384);
-   x.shrink_to_fit(p384_limbs + 1);
+   x.resize(p384_limbs + 1);
 
    int64_t S = 0;