5 files changed, 9 insertions, 11 deletions
diff --git a/src/math/bigint/bigint.cpp b/src/math/bigint/bigint.cpp
index a13c4f234..a49335e75 100644
--- a/src/math/bigint/bigint.cpp
+++ b/src/math/bigint/bigint.cpp
@@ -184,7 +184,7 @@ bool BigInt::get_bit(size_t n) const
 /*
 * Return bits {offset...offset+length}
 */
-size_t BigInt::get_substring(size_t offset, size_t length) const
+u32bit BigInt::get_substring(size_t offset, size_t length) const
    {
    if(length > 32)
       throw Invalid_Argument("BigInt::get_substring: Substring size too big");
@@ -196,7 +196,7 @@ size_t BigInt::get_substring(size_t offset, size_t length) const
    u64bit mask = (1 << length) - 1;
    size_t shift = (offset % 8);
 
-   return static_cast<size_t>((piece >> shift) & mask);
+   return static_cast<u32bit>((piece >> shift) & mask);
    }
 
 /*
diff --git a/src/math/bigint/bigint.h b/src/math/bigint/bigint.h
index 0c01d56c1..fc2e58073 100644
--- a/src/math/bigint/bigint.h
+++ b/src/math/bigint/bigint.h
@@ -135,7 +135,7 @@ class BOTAN_DLL BigInt
      * @param i a word index
      * @return the word at index i
      */
-     word operator[](size_t i) const { return reg[i]; }
+     const word& operator[](size_t i) const { return reg[i]; }
 
      /**
      * Zeroize the BigInt
@@ -215,7 +215,7 @@ class BOTAN_DLL BigInt
      * @result the integer extracted from the register starting at
      * offset with specified length
      */
-     size_t get_substring(size_t offset, size_t length) const;
+     u32bit get_substring(size_t offset, size_t length) const;
 
      /**
      * @param n the offset to get a byte from
diff --git a/src/math/numbertheory/point_gfp.cpp b/src/math/numbertheory/point_gfp.cpp
index 5da1959bc..8cb40270c 100644
--- a/src/math/numbertheory/point_gfp.cpp
+++ b/src/math/numbertheory/point_gfp.cpp
@@ -324,12 +324,12 @@ PointGFp operator*(const BigInt& scalar, const PointGFp& point)
 
    while(bits_left >= window_size)
       {
-      size_t nibble = scalar.get_substring(bits_left - window_size,
-                                           window_size);
-
       for(size_t i = 0; i != window_size; ++i)
          H.mult2(ws);
 
+      const u32bit nibble = scalar.get_substring(bits_left - window_size,
+                                                 window_size);
+
       if(nibble)
          H.add(Ps[nibble-1], ws);
 
diff --git a/src/math/numbertheory/powm_fw.cpp b/src/math/numbertheory/powm_fw.cpp
index afc53f233..3348e55cd 100644
--- a/src/math/numbertheory/powm_fw.cpp
+++ b/src/math/numbertheory/powm_fw.cpp
@@ -45,8 +45,7 @@ BigInt Fixed_Window_Exponentiator::execute() const
       for(size_t k = 0; k != window_bits; ++k)
          x = reducer.square(x);
 
-      size_t nibble = exp.get_substring(window_bits*(j-1), window_bits);
-      if(nibble)
+      if(u32bit nibble = exp.get_substring(window_bits*(j-1), window_bits))
          x = reducer.multiply(x, g[nibble-1]);
       }
    return x;
diff --git a/src/math/numbertheory/powm_mnt.cpp b/src/math/numbertheory/powm_mnt.cpp
index 038ce14da..4f626ac9d 100644
--- a/src/math/numbertheory/powm_mnt.cpp
+++ b/src/math/numbertheory/powm_mnt.cpp
@@ -90,8 +90,7 @@ BigInt Montgomery_Exponentiator::execute() const
          x.get_reg().set(&z[0], mod_words + 1);
          }
 
-      size_t nibble = exp.get_substring(window_bits*(i-1), window_bits);
-      if(nibble)
+      if(u32bit nibble = exp.get_substring(window_bits*(i-1), window_bits))
          {
          const BigInt& y = g[nibble-1];