Botan::CT Namespace Reference

Functions
template<typename T>
void	cond_zero_mem (T cond, T *array, size_t elems)
template<typename T>
void	conditional_copy_mem (T value, T *to, const T *from0, const T *from1, size_t elems)
template<typename T>
T	expand_mask (T x)
template<typename T>
T	expand_top_bit (T a)
template<typename T>
T	is_equal (T x, T y)
template<typename T>
T	is_less (T x, T y)
template<typename T>
T	is_lte (T x, T y)
template<typename T>
T	is_zero (T x)
template<typename T>
T	max (T a, T b)
template<typename T>
T	min (T a, T b)
template<typename T>
T	select (T mask, T from0, T from1)
template<typename PredT, typename ValT>
ValT	val_or_zero (PredT pred_val, ValT val)

Function Documentation

cond_zero_mem()

template<typename T>

void Botan::CT::cond_zero_mem ( T cond, T * array, size_t elems )

inline

Definition at line 100 of file ct_utils.h.

   {
   const T mask = CT::expand_mask(cond);
   const T zero(0);
 
   for(size_t i = 0; i != elems; ++i)
      {
      array[i] = CT::select(mask, zero, array[i]);
      }
   }

References cond_zero_mem(), expand_mask(), and select().

Referenced by cond_zero_mem().

conditional_copy_mem()

template<typename T>

void Botan::CT::conditional_copy_mem ( T value, T * to, const T * from0, const T * from1, size_t elems )

inline

Definition at line 85 of file ct_utils.h.

   {
   const T mask = CT::expand_mask(value);
 
   for(size_t i = 0; i != elems; ++i)
      {
      to[i] = CT::select(mask, from0[i], from1[i]);
      }
   }

References conditional_copy_mem(), expand_mask(), and select().

Referenced by conditional_copy_mem().

expand_mask()

template<typename T>

T Botan::CT::expand_mask ( T x )

inline

Definition at line 33 of file ct_utils.h.

   {
   T r = x;
   // First fold r down to a single bit
   for(size_t i = 1; i != sizeof(T)*8; i *= 2)
      r |= r >> i;
   r &= 1;
   r = ~(r - 1);
   return r;
   }

References expand_mask().

Referenced by Botan::bigint_cnd_abs(), Botan::bigint_cnd_add(), Botan::bigint_cnd_sub(), Botan::bigint_cnd_swap(), cond_zero_mem(), conditional_copy_mem(), expand_mask(), expand_top_bit(), is_less(), is_lte(), is_zero(), and val_or_zero().

expand_top_bit()

template<typename T>

T Botan::CT::expand_top_bit ( T a )

inline

Definition at line 114 of file ct_utils.h.

   {
   return expand_mask<T>(a >> (sizeof(T)*8-1));
   }

References expand_mask(), and expand_top_bit().

Referenced by expand_top_bit(), max(), and min().

is_equal()

template<typename T>

T Botan::CT::is_equal ( T x, T y )

inline

Definition at line 63 of file ct_utils.h.

   {
   return is_zero(x ^ y);
   }

References is_equal(), and is_zero().

Referenced by Botan::BigInt::const_time_lookup(), and is_equal().

is_less()

template<typename T>

T Botan::CT::is_less ( T x, T y )

inline

Definition at line 69 of file ct_utils.h.

   {
   /*
   This expands to a constant time sequence with GCC 5.2.0 on x86-64
   but something more complicated may be needed for portable const time.
   */
   return expand_mask<T>(x < y);
   }

References expand_mask(), and is_less().

Referenced by is_less().

is_lte()

template<typename T>

T Botan::CT::is_lte ( T x, T y )

inline

Definition at line 79 of file ct_utils.h.

   {
   return expand_mask<T>(x <= y);
   }

References expand_mask(), and is_lte().

Referenced by is_lte().

is_zero()

template<typename T>

T Botan::CT::is_zero ( T x )

inline

Definition at line 57 of file ct_utils.h.

   {
   return ~expand_mask(x);
   }

References expand_mask(), and is_zero().

Referenced by is_equal(), and is_zero().

max()

template<typename T>

T Botan::CT::max ( T a, T b )

inline

Definition at line 120 of file ct_utils.h.

   {
   const T a_larger = b - a; // negative if a is larger
   return select(expand_top_bit(a), a, b);
   }

References expand_top_bit(), max(), and select().

Referenced by max().

min()

template<typename T>

T Botan::CT::min ( T a, T b )

inline

Definition at line 127 of file ct_utils.h.

   {
   const T a_larger = b - a; // negative if a is larger
   return select(expand_top_bit(b), b, a);
   }

References expand_top_bit(), min(), and select().

Referenced by min().

select()

template<typename T>

T Botan::CT::select ( T mask, T from0, T from1 )

inline

Definition at line 45 of file ct_utils.h.

   {
   return (from0 & mask) | (from1 & ~mask);
   }

References select().

Referenced by Botan::bigint_cnd_abs(), Botan::bigint_cnd_add(), Botan::bigint_cnd_sub(), Botan::bigint_cnd_swap(), cond_zero_mem(), conditional_copy_mem(), Botan::BigInt::const_time_lookup(), max(), min(), select(), and val_or_zero().

val_or_zero()

template<typename PredT, typename ValT>

ValT Botan::CT::val_or_zero ( PredT pred_val, ValT val )

inline

Definition at line 51 of file ct_utils.h.

   {
   return select(CT::expand_mask<ValT>(pred_val), val, static_cast<ValT>(0));
   }

References expand_mask(), select(), and val_or_zero().

Referenced by val_or_zero().