liblinux++

commit cf6f735c777f6f3313c16d2cdf28009dd0ffbdaf
parent e73acf0554f059c01739e12aa2a18301943a3d6b
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Sun, 28 Dec 2025 01:29:44 +0000

Improve vector

Diffstat:
M
writer.cpp
 | 
78
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------

1 file changed, 63 insertions(+), 15 deletions(-)
diff --git a/writer.cpp b/writer.cpp
@@ -1,5 +1,10 @@
 #include "linux.hpp"
 
+void* operator new(size_t, void* p) noexcept
+{
+	return p;
+}
+
 struct writer
 {
 	virtual void write(span<char const>) = 0;
@@ -21,24 +26,68 @@ private:
 };
 
 template <typename T>
+T div_round_up(T n, T d)
+{
+	return (n + (d-1)) / d;
+}
+
+size_t next_power_of_two(size_t n)
+{
+	if (not n)
+		return n;
+	--n;
+	for (unsigned i = 1; i <= 32; i <<= 1)
+		n |= n >> i;
+	return ++n;
+}
+
+template <typename T>
 struct vector
 {
-	void push_back(T c)
+	vector() = default;
+	~vector()
 	{
-		if (used * sizeof(T) >= capacity)
+		for (auto p = buf + used; p != buf; --p)
+			p->~T();
+		if (buf)
+			*munmap(buf, capacity);
+	}
+	vector(vector const& old)
+	{
+		reserve(old.size());
+		push_back(old);
+	}
+	vector& operator =(vector const&) = delete; // todo: clear, assign
+
+	void reserve(size_t min)
+	{
+		min *= sizeof(T);
+		if (min <= capacity)
+			return;
+		min = min <= 4096u ? 4096u : next_power_of_two(min);
+		auto new_buf = reinterpret_cast<T*>(*mmap(nullptr, min, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, {}, 0));
+		for (size_t i = 0; i < used; ++i)
 		{
-			size_t const old_cap = capacity;
-			size_t const new_cap = capacity ? capacity * 2 : 0x1000;
-			T* new_buf = (T*)*mmap(nullptr, new_cap, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, {}, 0);
-			for (size_t i = 0; i < used; ++i)
-				new_buf[i] = buf[i];
-			capacity = new_cap;
-			if (buf)
-				*munmap(buf, old_cap);
-			buf = new_buf;
+			new (new_buf + i) T{buf[i]};
+			buf[i].~T();
 		}
-
-		buf[used++] = c;
+		if (buf)
+			*munmap(buf, capacity);
+		buf = new_buf;
+		capacity = min;
+	}
+	void push_back(T c)
+	{
+		reserve(used + 1);
+		new (buf + used++) T{c};
+	}
+	void push_back(span<T const> data)
+	{
+		reserve(size() + data.size());
+		T* p = buf + used;
+		for (auto const& x : data)
+			new (p++) T{x};
+		used = p - buf;
 	}
 
 	T const* data() const { return buf; }
@@ -55,8 +104,7 @@ struct buf_writer : writer
 
 	void write(span<char const> data) override
 	{
-		for (char c : data)
-			buffer.push_back(c);
+		buffer.push_back(data);
 	}
 	span<char const> get() const noexcept
 	{