Make a few simple functions constexpr

This is primarily just to verify that C++11 constexpr works.

6 files changed, 29 insertions, 32 deletions

diff --git a/src/lib/block/aes/aes.cpp b/src/lib/block/aes/aes.cpp
index c025530a4..0c18e93ee 100644
--- a/src/lib/block/aes/aes.cpp
+++ b/src/lib/block/aes/aes.cpp
@@ -99,15 +99,15 @@ const uint8_t SD[256] = {
    0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 0xE1, 0x69, 0x14, 0x63,
    0x55, 0x21, 0x0C, 0x7D };
 
-inline uint8_t xtime(uint8_t s) { return static_cast<uint8_t>(s << 1) ^ ((s >> 7) * 0x1B); }
-inline uint8_t xtime4(uint8_t s) { return xtime(xtime(s)); }
-inline uint8_t xtime8(uint8_t s) { return xtime(xtime(xtime(s))); }
-
-inline uint8_t xtime3(uint8_t s) { return xtime(s) ^ s; }
-inline uint8_t xtime9(uint8_t s) { return xtime8(s) ^ s; }
-inline uint8_t xtime11(uint8_t s) { return xtime8(s) ^ xtime(s) ^ s; }
-inline uint8_t xtime13(uint8_t s) { return xtime8(s) ^ xtime4(s) ^ s; }
-inline uint8_t xtime14(uint8_t s) { return xtime8(s) ^ xtime4(s) ^ xtime(s); }
+inline constexpr uint8_t xtime(uint8_t s) { return static_cast<uint8_t>(s << 1) ^ ((s >> 7) * 0x1B); }
+inline constexpr uint8_t xtime4(uint8_t s) { return xtime(xtime(s)); }
+inline constexpr uint8_t xtime8(uint8_t s) { return xtime(xtime(xtime(s))); }
+
+inline constexpr uint8_t xtime3(uint8_t s) { return xtime(s) ^ s; }
+inline constexpr uint8_t xtime9(uint8_t s) { return xtime8(s) ^ s; }
+inline constexpr uint8_t xtime11(uint8_t s) { return xtime8(s) ^ xtime(s) ^ s; }
+inline constexpr uint8_t xtime13(uint8_t s) { return xtime8(s) ^ xtime4(s) ^ s; }
+inline constexpr uint8_t xtime14(uint8_t s) { return xtime8(s) ^ xtime4(s) ^ xtime(s); }
 
 inline uint32_t SE_word(uint32_t x)
    {
diff --git a/src/lib/utils/bit_ops.h b/src/lib/utils/bit_ops.h
index c7e401492..a9924b232 100644
--- a/src/lib/utils/bit_ops.h
+++ b/src/lib/utils/bit_ops.h
@@ -22,7 +22,7 @@ namespace Botan {
 * @return true iff arg is 2^n for some n > 0
 */
 template<typename T>
-inline bool is_power_of_2(T arg)
+inline constexpr bool is_power_of_2(T arg)
    {
    return ((arg != 0 && arg != 1) && ((arg & (arg-1)) == 0));
    }
diff --git a/src/lib/utils/ct_utils.h b/src/lib/utils/ct_utils.h
index f4f881871..0303d2a6c 100644
--- a/src/lib/utils/ct_utils.h
+++ b/src/lib/utils/ct_utils.h
@@ -78,14 +78,14 @@ inline void unpoison(T& p)
 /* Mask generation */
 
 template<typename T>
-inline T expand_top_bit(T a)
+inline constexpr T expand_top_bit(T a)
    {
    static_assert(std::is_unsigned<T>::value, "unsigned integer type required");
    return static_cast<T>(0) - (a >> (sizeof(T)*8-1));
    }
 
 template<typename T>
-inline T is_zero(T x)
+inline constexpr T is_zero(T x)
    {
    static_assert(std::is_unsigned<T>::value, "unsigned integer type required");
    return expand_top_bit<T>(~x & (x - 1));
@@ -100,51 +100,51 @@ inline T is_zero(T x)
 * select.
 */
 template<typename T>
-inline T expand_mask(T x)
+inline constexpr T expand_mask(T x)
    {
    static_assert(std::is_unsigned<T>::value, "unsigned integer type required");
    return ~is_zero(x);
    }
 
 template<typename T>
-inline T select(T mask, T from0, T from1)
+inline constexpr T select(T mask, T from0, T from1)
    {
    static_assert(std::is_unsigned<T>::value, "unsigned integer type required");
    return static_cast<T>((from0 & mask) | (from1 & ~mask));
    }
 
 template<typename T>
-inline T select2(T mask0, T val0, T mask1, T val1, T val2)
+inline constexpr T select2(T mask0, T val0, T mask1, T val1, T val2)
    {
    return select<T>(mask0, val0, select<T>(mask1, val1, val2));
    }
 
 template<typename T>
-inline T select3(T mask0, T val0, T mask1, T val1, T mask2, T val2, T val3)
+inline constexpr T select3(T mask0, T val0, T mask1, T val1, T mask2, T val2, T val3)
    {
    return select2<T>(mask0, val0, mask1, val1, select<T>(mask2, val2, val3));
    }
 
 template<typename PredT, typename ValT>
-inline ValT val_or_zero(PredT pred_val, ValT val)
+inline constexpr ValT val_or_zero(PredT pred_val, ValT val)
    {
    return select(CT::expand_mask<ValT>(pred_val), val, static_cast<ValT>(0));
    }
 
 template<typename T>
-inline T is_equal(T x, T y)
+inline constexpr T is_equal(T x, T y)
    {
    return is_zero<T>(x ^ y);
    }
 
 template<typename T>
-inline T is_less(T a, T b)
+inline constexpr T is_less(T a, T b)
    {
    return expand_top_bit<T>(a ^ ((a^b) | ((a-b)^a)));
    }
 
 template<typename T>
-inline T is_lte(T a, T b)
+inline constexpr T is_lte(T a, T b)
    {
    return CT::is_less(a, b) | CT::is_equal(a, b);
    }
diff --git a/src/lib/utils/loadstor.h b/src/lib/utils/loadstor.h
index 70ad20591..2fb1543b0 100644
--- a/src/lib/utils/loadstor.h
+++ b/src/lib/utils/loadstor.h
@@ -36,7 +36,7 @@ namespace Botan {
 * @param input the value to extract from
 * @return byte byte_num of input
 */
-template<typename T> inline uint8_t get_byte(size_t byte_num, T input)
+template<typename T> inline constexpr uint8_t get_byte(size_t byte_num, T input)
    {
    return static_cast<uint8_t>(
       input >> (((~byte_num)&(sizeof(T)-1)) << 3)
@@ -49,7 +49,7 @@ template<typename T> inline uint8_t get_byte(size_t byte_num, T input)
 * @param i1 the second byte
 * @return i0 || i1
 */
-inline uint16_t make_uint16(uint8_t i0, uint8_t i1)
+inline constexpr uint16_t make_uint16(uint8_t i0, uint8_t i1)
    {
    return static_cast<uint16_t>((static_cast<uint16_t>(i0) << 8) | i1);
    }
@@ -62,7 +62,7 @@ inline uint16_t make_uint16(uint8_t i0, uint8_t i1)
 * @param i3 the fourth byte
 * @return i0 || i1 || i2 || i3
 */
-inline uint32_t make_uint32(uint8_t i0, uint8_t i1, uint8_t i2, uint8_t i3)
+inline constexpr uint32_t make_uint32(uint8_t i0, uint8_t i1, uint8_t i2, uint8_t i3)
    {
    return ((static_cast<uint32_t>(i0) << 24) |
            (static_cast<uint32_t>(i1) << 16) |
@@ -82,8 +82,8 @@ inline uint32_t make_uint32(uint8_t i0, uint8_t i1, uint8_t i2, uint8_t i3)
 * @param i7 the eighth byte
 * @return i0 || i1 || i2 || i3 || i4 || i5 || i6 || i7
 */
-inline uint64_t make_uint64(uint8_t i0, uint8_t i1, uint8_t i2, uint8_t i3,
-                          uint8_t i4, uint8_t i5, uint8_t i6, uint8_t i7)
+inline constexpr uint64_t make_uint64(uint8_t i0, uint8_t i1, uint8_t i2, uint8_t i3,
+                                      uint8_t i4, uint8_t i5, uint8_t i6, uint8_t i7)
     {
    return ((static_cast<uint64_t>(i0) << 56) |
            (static_cast<uint64_t>(i1) << 48) |
diff --git a/src/lib/utils/rotate.h b/src/lib/utils/rotate.h
index 4bb76c9ed..d927b93b7 100644
--- a/src/lib/utils/rotate.h
+++ b/src/lib/utils/rotate.h
@@ -18,7 +18,7 @@ namespace Botan {
 * @return input rotated left by ROT bits
 */
 template<size_t ROT, typename T>
-inline T rotl(T input)
+inline constexpr T rotl(T input)
    {
    static_assert(ROT > 0 && ROT < 8*sizeof(T), "Invalid rotation constant");
    return static_cast<T>((input << ROT) | (input >> (8*sizeof(T) - ROT)));
@@ -30,7 +30,7 @@ inline T rotl(T input)
 * @return input rotated right by ROT bits
 */
 template<size_t ROT, typename T>
-inline T rotr(T input)
+inline constexpr T rotr(T input)
    {
    static_assert(ROT > 0 && ROT < 8*sizeof(T), "Invalid rotation constant");
    return static_cast<T>((input >> ROT) | (input << (8*sizeof(T) - ROT)));
diff --git a/src/lib/utils/rounding.h b/src/lib/utils/rounding.h
index a03e3a4ee..ae0aedf07 100644
--- a/src/lib/utils/rounding.h
+++ b/src/lib/utils/rounding.h
@@ -34,12 +34,9 @@ inline size_t round_up(size_t n, size_t align_to)
 * @return n rounded down to a multiple of align_to
 */
 template<typename T>
-inline T round_down(T n, T align_to)
+inline constexpr T round_down(T n, T align_to)
    {
-   if(align_to == 0)
-      return n;
-
-   return (n - (n % align_to));
+   return (align_to == 0) ? n : (n - (n % align_to));
    }
 
 /**