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Implement recursive reverse.

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This commit is contained in:
Thomas Harte
2025-02-03 23:50:15 -05:00
parent e5945fbb3d
commit e1a7dd9b24
2 changed files with 25 additions and 13 deletions
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Numeric/CRC.hpp
+24 -12
View File
@@ -16,7 +16,23 @@
namespace CRC {
constexpr uint8_t reverse_byte(uint8_t byte) {
template <typename IntT>
constexpr IntT reverse(const IntT source) {
static_assert(std::is_same_v<IntT, uint16_t> || std::is_same_v<IntT, uint32_t> || std::is_same_v<IntT, uint64_t>);
using HalfIntT =
std::conditional_t<std::is_same_v<IntT, uint16_t>, uint8_t,
std::conditional_t<std::is_same_v<IntT, uint32_t>, uint16_t,
uint32_t>>;
constexpr auto HalfShift = sizeof(IntT) * 4;
return IntT(
IntT(reverse(HalfIntT(source))) << HalfShift) |
IntT(reverse(HalfIntT(source >> HalfShift))
);
}
template <>
constexpr uint8_t reverse<uint8_t>(const uint8_t byte) {
return
((byte & 0x80) ? 0x01 : 0x00) |
((byte & 0x40) ? 0x02 : 0x00) |
@@ -64,26 +80,22 @@ public:
return table;
} ();
if constexpr (reflect_input) byte = reverse_byte(byte);
if constexpr (reflect_input) byte = reverse(byte);
value_ = IntType((value_ << 8) ^ xor_table[(value_ >> multibyte_shift) ^ byte]);
}
/// @returns The current value of the CRC.
inline IntType get_value() const {
IntType result = value_ ^ output_xor;
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;
return reverse(result);
} else {
return result;
}
return result;
}
/// Sets the current value of the CRC.
inline void set_value(IntType value) { value_ = value; }
inline void set_value(const IntType value) { value_ = value; }
/*!
A compound for:
@@ -103,7 +115,7 @@ public:
[add all data from @c begin to @c end]
get_value()
*/
template <typename Iterator> IntType compute_crc(Iterator begin, Iterator end) {
template <typename Iterator> IntType compute_crc(Iterator begin, const Iterator end) {
reset();
while(begin != end) {
add(*begin);
Storage/Tape/Parsers/Spectrum.cpp
+1 -1
View File
@@ -212,7 +212,7 @@ std::optional<uint8_t> Parser::get_byte(Storage::Tape::TapeSerialiser &serialise
}
if(should_flip_bytes()) {
result = CRC::reverse_byte(result);
result = CRC::reverse(result);
}
checksum_ ^= result;