Promote ct_is_zero and expand_top_bit to bit_ops.h

2 files changed, 21 insertions, 10 deletions

diff --git a/src/lib/utils/bit_ops.h b/src/lib/utils/bit_ops.h
index f32250b9c..75cefbdfa 100644
--- a/src/lib/utils/bit_ops.h
+++ b/src/lib/utils/bit_ops.h
@@ -17,6 +17,24 @@
 namespace Botan {
 
 /**
+* If top bit of arg is set, return ~0. Otherwise return 0.
+*/
+template<typename T>
+inline T expand_top_bit(T a)
+   {
+   return static_cast<T>(0) - (a >> (sizeof(T)*8-1));
+   }
+
+/**
+* If arg is zero, return ~0. Otherwise return 0
+*/
+template<typename T>
+inline T ct_is_zero(T x)
+   {
+   return expand_top_bit<T>(~x & (x - 1));
+   }
+
+/**
 * Power of 2 test. T should be an unsigned integer type
 * @param arg an integer value
 * @return true iff arg is 2^n for some n > 0
diff --git a/src/lib/utils/ct_utils.h b/src/lib/utils/ct_utils.h
index 72be79114..941df839a 100644
--- a/src/lib/utils/ct_utils.h
+++ b/src/lib/utils/ct_utils.h
@@ -15,6 +15,7 @@
 #define BOTAN_CT_UTILS_H_
 
 #include <botan/secmem.h>
+#include <botan/internal/bit_ops.h>
 #include <type_traits>
 #include <vector>
 
@@ -139,7 +140,7 @@ class Mask
       */
       static Mask<T> is_zero(T x)
          {
-         return Mask<T>(expand_top_bit(~x & (x - 1)));
+         return Mask<T>(ct_is_zero<T>(x));
          }
 
       /**
@@ -155,7 +156,7 @@ class Mask
       */
       static Mask<T> is_lt(T x, T y)
          {
-         return Mask<T>(expand_top_bit(x^((x^y) | ((x-y)^x))));
+         return Mask<T>(expand_top_bit<T>(x^((x^y) | ((x-y)^x))));
          }
 
       /**
@@ -329,14 +330,6 @@ class Mask
          }
 
    private:
-      /**
-      * If top bit of arg is set, return ~0. Otherwise return 0.
-      */
-      static T expand_top_bit(T a)
-         {
-         return static_cast<T>(0) - (a >> (sizeof(T)*8-1));
-         }
-
       Mask(T m) : m_mask(m) {}
 
       T m_mask;