wallet/mpir_and_base58.h

#pragma once
/*  This header handles the stuff related to arbitrary precision arithmetic values*/

namespace mpir {
	class mpz {
		mpz_t mpz_m;
	public:
		mpz() {
			mpz_init2(mpz_m, 624);
		}
		mpz(const char* str, int base) {
			mpz_init(mpz_m);
			if (mpz_set_str(mpz_m, str, base))throw BadDataException();
		}
		~mpz() {
			mpz_clear(mpz_m);
		}
		operator mpz_ptr() {
			return mpz_m;
		}
	};

	extern 	mpz ristretto25519_curve_order;
}



//	This global thread local object is explicitly constructed
//	on the heap in the code on need once the thread starts running
//	and destroyed when the thread exits.
//	This explicit construction and destruction is a workaround because C++ lacks
//	support for concurrent processes
//	and is therefore unable to correctly handle non pod thread local objects.  It will
//	not correctly construct and
//	destruct thread_local objects by itself, because the model machine does not have a model
//	for threading.  It has a pile of matchsticks and a tub of glue with which you can build 
//	your own model.  It supports all the stuff you need for threads, but has no idea how all
//	these moving parts fit together.
//	So you have to construct and destruct your non pod thread local objects in code.
class thread_local__ {
public:
	//	These exist to avoid the high cost of repeatedly creating and destroying temporary mpz objects.
	//	They are expensive to create and destroy, because they use heap allocation.
	//	These are used all over the place as temporaries.
	mpir::mpz q, r, n;
};
extern thread_local thread_local__*thl;	//Constructor in app.obj.  
//	Destructor does not seem to get called, hence using a pointer
//	and destroying explicitly, rather than an std::unique_ptr
//	needs testing to figure out what is going on

namespace ro {
	using ristretto255::scalar, ristretto255::point;

	auto fasthash(uint64_t, std::span<const uint64_t>)->uint32_t;
	void right_justify_string(char*, char*);
	bool is_alphanumeric_fixed_length(unsigned int, const char*);

	template <class T> typename std::enable_if<
		ro::is_blob_field_type<T>::value,
		decltype(T::type_indentifier, uint32_t())
	>::type fasthash(const T& p_blob) {
		static_assert(sizeof(T) % 8 == 0, "fasthash assumes a multiple of 8 bytes");
		return fasthash(
			T::type_indentifier,
			std::span< const uint64_t >(
				reinterpret_cast<const uint64_t*>(&p_blob.blob[0]),
				p_blob.blob.size() / 8
				)
		);
	}

	void map_base_from_mpir58(char*);
	void map_base_to_mpir58(const char*, char*, size_t);

	template <typename T> class base58 : public CompileSizedString<
		((sizeof(T) * 8 + 4) * 4943ui64 + 28955ui64) / 28956ui64 - (std::is_same_v<T, scalar> ? 1 : 0)> {
	public:
		//	The rational number 4943 / 28956 is minisculy larger than log(2)/log(58)
		//	hence rounding up the nearest integer guarantees it will always be big enough.
		base58() = default;
		~base58() = default;
		base58(const T&);
		base58(const char* p);
		static const char* bin(
			typename const decltype(T::type_indentifier, char())* p,
			T& sc
		);
		static void bin(const base58<T>& str, T& sc);
		static T bin(const char* str) {
			T sc;
			bin(str, sc);
			return sc;
		};
		T bin() const {
			T sc;
			bin(*this, sc);
			return sc;
		};
		operator T() const {
			return bin();
		}
	};

	template <class T> typename const decltype(base58<T>::length, T::type_indentifier, uint32_t())
		//		cannot be consteval or constexpr, because has to be called after the mpir temp values are constructed
		check_range() {
		if (thl == nullptr)thl = new thread_local__();
		mpz_ui_pow_ui(thl->n, 58, base58<T>::length);

		if constexpr (std::is_same_v<T, scalar>) {
			mpz_fdiv_q(thl->q, thl->n, mpir::ristretto25519_curve_order);
		}
		else {
			mpz_fdiv_q_2exp(thl->q, thl->n, sizeof(T) * 8);
		}
		assert(mpz_cmp_ui(thl->q, UINT32_MAX) <= 0);
		return static_cast<uint32_t>(mpz_get_ui(thl->q));
	}

	template <class T> const uint32_t check_range_m{ check_range<T>() };

	template <class T> const char* base58<T>::bin(
		typename const decltype(T::type_indentifier, char())* p,
		T& sc
	) {
		const uint32_t range = check_range_m<T>;
		base58 strsc;
		char* ps = strsc;
		map_base_to_mpir58(p, ps, strsc.length);
		if (p[base58::length] > ' ')throw OversizeBase58String();
		if (mpz_set_str(thl->n, ps, 58))throw BadStringRepresentationOfCryptoIdException();
		if constexpr (std::is_same_v<T, scalar>) {
			mpz_fdiv_qr(thl->q, thl->r, thl->n, mpir::ristretto25519_curve_order);
		}
		else {
			mpz_fdiv_q_2exp(thl->q, thl->n, sizeof(sc.blob) * 8);
			mpz_fdiv_r_2exp(thl->r, thl->n, sizeof(sc.blob) * 8);
		}
		size_t count;
		mpz_export(&(sc.blob[0]), &count, -1, 1, -1, 0, thl->r);
		if (count < sizeof(sc.blob))memset(&sc.blob[count], 0, sizeof(sc.blob) - count);
		mpir_ui ck{ (static_cast<uint64_t>(fasthash(sc)) * static_cast<uint64_t>(range)) >> 32 };
		if (ck != mpz_get_ui(thl->q)) throw BadStringRepresentationOfCryptoIdException();
		return p + base58<T>::length;
	}

	template <class T> char* to_base58(
		//	does no string memory allocation, p has to point into a buffer,
		//	return value points to next position in the buffer, which is now null
		typename decltype(check_range_m<T>, char())* p,
		const T& sc
	) {
		mpir_ui ck{ (static_cast<uint64_t>(fasthash(sc)) * static_cast<uint64_t>(check_range_m<T>)) >> 32 };
		mpz_import(thl->n, sizeof(sc.blob), -1, 1, -1, 0, &sc.blob[0]);
		if constexpr (std::is_same_v<T, scalar>) {
			mpz_addmul_ui(thl->n, mpir::ristretto25519_curve_order, ck);
		}
		else {
			mpz_set_ui(thl->r, ck);
			mpz_mul_2exp(thl->r, thl->r, sizeof(sc.blob) * 8);
			mpz_add(thl->n, thl->n, thl->r);
		}
		mpz_get_str(p, 58, thl->n);
		char* terminal_null{ p + sizeof(base58<T>) - 1 };
		right_justify_string(p, terminal_null);
		map_base_from_mpir58(p);
		return terminal_null;
		//	return value points to trailing null
	}

	template <class T> base58<T>::base58(const T& el) {
		to_base58<T>(static_cast<char*>(*this), el);
	}

	template <class T> base58<T>::base58(const char* p) {
		memmove(this, p, (this->length));
		std::array<char, (this->length)> test;
		map_base_to_mpir58(this, test, this->length);	//Force an exception for bad char
		if (p[this->length] > ' ')throw OversizeBase58String();
		this->operator char* [this->length] = '\0';
	}
}