mirror of
https://github.com/TomHarte/CLK.git
synced 2024-11-22 12:33:29 +00:00
84 lines
2.3 KiB
C++
84 lines
2.3 KiB
C++
//
|
|
// Carry.hpp
|
|
// Clock Signal
|
|
//
|
|
// Created by Thomas Harte on 30/08/2023.
|
|
// Copyright © 2023 Thomas Harte. All rights reserved.
|
|
//
|
|
|
|
#ifndef Carry_hpp
|
|
#define Carry_hpp
|
|
|
|
#include <limits>
|
|
|
|
namespace Numeric {
|
|
|
|
/// @returns @c true if from @c bit there was:
|
|
/// • carry after calculating @c lhs + @c rhs if @c is_add is true; or
|
|
/// • borrow after calculating @c lhs - @c rhs if @c is_add is false;
|
|
/// producing @c result.
|
|
template <bool is_add, int bit, typename IntT> bool carried_out(IntT lhs, IntT rhs, IntT result) {
|
|
// Additive:
|
|
//
|
|
// 0 and 0 => didn't.
|
|
// 0 and 1 or 1 and 0 => did if 0.
|
|
// 1 and 1 => did.
|
|
//
|
|
// Subtractive:
|
|
//
|
|
// 1 and 0 => didn't
|
|
// 1 and 1 or 0 and 0 => did if 1.
|
|
// 0 and 1 => did.
|
|
if constexpr (!is_add) {
|
|
rhs = ~rhs;
|
|
}
|
|
const bool carry = IntT(1 << bit) & (lhs | rhs) & ((lhs & rhs) | ~result);
|
|
if constexpr (!is_add) {
|
|
return !carry;
|
|
} else {
|
|
return carry;
|
|
}
|
|
}
|
|
|
|
/// @returns @c true if there was carry into @c bit when computing either:
|
|
/// • @c lhs + @c rhs; or
|
|
/// • @c lhs - @c rhs;
|
|
/// producing @c result.
|
|
template <int bit, typename IntT> bool carried_in(IntT lhs, IntT rhs, IntT result) {
|
|
// 0 and 0 or 1 and 1 => did if 1.
|
|
// 0 and 1 or 1 and 0 => did if 0.
|
|
return IntT(1 << bit) & (lhs ^ rhs ^ result);
|
|
}
|
|
|
|
/// @returns An int of type @c IntT with only the most-significant bit set.
|
|
template <typename IntT> constexpr IntT top_bit() {
|
|
static_assert(!std::numeric_limits<IntT>::is_signed);
|
|
constexpr IntT max = std::numeric_limits<IntT>::max();
|
|
return max - (max >> 1);
|
|
}
|
|
|
|
/// @returns The number of bits in @c IntT.
|
|
template <typename IntT> constexpr int bit_size() {
|
|
return sizeof(IntT) * 8;
|
|
}
|
|
|
|
/// @returns An int with the top bit indicating whether overflow occurred during the calculation of
|
|
/// • @c lhs + @c rhs (if @c is_add is true); or
|
|
/// • @c lhs - @c rhs (if @c is_add is false)
|
|
/// and the result was @c result. All other bits will be clear.
|
|
template <bool is_add, typename IntT>
|
|
IntT overflow(IntT lhs, IntT rhs, IntT result) {
|
|
const IntT output_changed = result ^ lhs;
|
|
const IntT input_differed = lhs ^ rhs;
|
|
|
|
if constexpr (is_add) {
|
|
return top_bit<IntT>() & output_changed & ~input_differed;
|
|
} else {
|
|
return top_bit<IntT>() & output_changed & input_differed;
|
|
}
|
|
}
|
|
|
|
}
|
|
|
|
#endif /* Carry_hpp */
|