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Renames T to the more-communicative IntType, adds some explicit constexpra.

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This commit is contained in:
Thomas Harte 2020-01-27 08:28:20 -05:00
parent 561e149058
commit 4b53f6a9f0
1 changed files with 20 additions and 20 deletions
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40
Numeric/CRC.hpp
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@ -15,19 +15,19 @@
namespace CRC {
/*! Provides a class capable of generating a CRC from source data. */
template <typename T, T reset_value, T xor_output, bool reflect_input, bool reflect_output> class Generator {
template <typename IntType, IntType reset_value, IntType output_xor, bool reflect_input, bool reflect_output> class Generator {
public:
/*!
Instantiates a CRC16 that will compute the CRC16 specified by the supplied
@c polynomial and @c reset_value.
*/
Generator(T polynomial): value_(reset_value) {
const T top_bit = T(~(T(~0) >> 1));
Generator(IntType polynomial): value_(reset_value) {
const IntType top_bit = IntType(~(IntType(~0) >> 1));
for(int c = 0; c < 256; c++) {
T shift_value = static_cast<T>(c << multibyte_shift);
IntType shift_value = IntType(c << multibyte_shift);
for(int b = 0; b < 8; b++) {
T exclusive_or = (shift_value&top_bit) ? polynomial : 0;
shift_value = static_cast<T>(shift_value << 1) ^ exclusive_or;
IntType exclusive_or = (shift_value&top_bit) ? polynomial : 0;
shift_value = IntType(shift_value << 1) ^ exclusive_or;
}
xor_table[c] = shift_value;
}
@ -38,17 +38,17 @@ template <typename T, T reset_value, T xor_output, bool reflect_input, bool refl
/// Updates the CRC to include @c byte.
void add(uint8_t byte) {
if(reflect_input) byte = reverse_byte(byte);
value_ = static_cast<T>((value_ << 8) ^ xor_table[(value_ >> multibyte_shift) ^ byte]);
if constexpr (reflect_input) byte = reverse_byte(byte);
value_ = IntType((value_ << 8) ^ xor_table[(value_ >> multibyte_shift) ^ byte]);
}
/// @returns The current value of the CRC.
inline T get_value() const {
T result = value_^xor_output;
if(reflect_output) {
T reflected_output = 0;
for(std::size_t c = 0; c < sizeof(T); ++c) {
reflected_output = T(reflected_output << 8) | T(reverse_byte(result & 0xff));
inline IntType get_value() const {
IntType result = value_ ^ output_xor;
if constexpr (reflect_output) {
IntType reflected_output = 0;
for(std::size_t c = 0; c < sizeof(IntType); ++c) {
reflected_output = IntType(reflected_output << 8) | IntType(reverse_byte(result & 0xff));
result >>= 8;
}
return reflected_output;
@ -57,7 +57,7 @@ template <typename T, T reset_value, T xor_output, bool reflect_input, bool refl
}
/// Sets the current value of the CRC.
inline void set_value(T value) { value_ = value; }
inline void set_value(IntType value) { value_ = value; }
/*!
A compound for:
@ -66,7 +66,7 @@ template <typename T, T reset_value, T xor_output, bool reflect_input, bool refl
[add all data from @c data]
get_value()
*/
template <typename Collection> T compute_crc(const Collection &data) {
template <typename Collection> IntType compute_crc(const Collection &data) {
return compute_crc(data.begin(), data.end());
}
@ -77,7 +77,7 @@ template <typename T, T reset_value, T xor_output, bool reflect_input, bool refl
[add all data from @c begin to @c end]
get_value()
*/
template <typename Iterator> T compute_crc(Iterator begin, Iterator end) {
template <typename Iterator> IntType compute_crc(Iterator begin, Iterator end) {
reset();
while(begin != end) {
add(*begin);
@ -87,9 +87,9 @@ template <typename T, T reset_value, T xor_output, bool reflect_input, bool refl
}
private:
static constexpr int multibyte_shift = (sizeof(T) * 8) - 8;
T xor_table[256];
T value_;
static constexpr int multibyte_shift = (sizeof(IntType) * 8) - 8;
IntType xor_table[256];
IntType value_;
constexpr uint8_t reverse_byte(uint8_t byte) const {
return