misc: Update README.md

Author: range3

README.md

@@ -1,6 +1,172 @@
-# lsm-tree
+# byte_span
 
-This is the lsm-tree project.
+`byte_span` is a lightweight view class for efficient handling of byte data. Based on the concept of `std::span`, it provides specialized functionality for byte data manipulation.
+
+## Features
+
+- Non-owning view type
+- Unified handling of byte-like types (`std::byte`, `char`, `unsigned char`)
+- View trivially copyable data types as byte sequences
+- Type-safe design using C++20 concepts
+- Zero-overhead abstraction
+
+## Basic Usage
+
+### 1. Creating from Byte Arrays
+
+The most basic usage is creating a `byte_span` from a byte array:
+
+```cpp
+std::byte data[4] = {
+    std::byte{0x00}, std::byte{0x01}, 
+    std::byte{0x02}, std::byte{0x03}
+};
+byte_span view{data};  // Deduced as byte_span<std::byte, 4>
+```
+
+### 2. Creating from std::array
+
+Easy creation from `std::array`:
+
+```cpp
+std::array<std::byte, 4> arr = {
+    std::byte{0x00}, std::byte{0x01}, 
+    std::byte{0x02}, std::byte{0x03}
+};
+byte_span view{arr};  // Deduced as byte_span<std::byte, 4>
+```
+
+### 3. Creating from std::vector
+
+You can create views from any contiguous container, including `std::vector`:
+
+```cpp
+// Integer data
+std::vector<int> numbers = {1, 2, 3, 4};
+byte_span view{numbers};  // View integers as bytes
+
+// Access underlying bytes
+auto first_byte = view[0];
+auto size_in_bytes = view.size();  // size = sizeof(int) * numbers.size()
+```
+
+### 4. Dynamic Size Views
+
+For runtime-sized views, use `dynamic_extent`:
+
+```cpp
+std::vector<std::byte> vec(100);
+byte_span view{vec};  // Deduced as byte_span<std::byte, dynamic_extent>
+```
+
+## Advanced Usage
+
+### 1. Using byte_view and cbyte_view
+
+The library provides two convenient type aliases:
+- `byte_view`: Mutable byte span (alias for `byte_span<std::byte>`)
+- `cbyte_view`: Immutable byte span (alias for `byte_span<const std::byte>`)
+
+Example usage in functions:
+
+```cpp
+// Function accepting read-only byte view
+void print_hex_dump(cbyte_view data) {
+    for (auto b : data) {
+        std::cout << std::format("{:02x} ", std::to_integer<int>(b));
+    }
+}
+
+// Function accepting mutable byte view
+void fill_pattern(byte_view data) {
+    for (size_t i = 0; i < data.size(); ++i) {
+        data[i] = std::byte{static_cast<unsigned char>(i & 0xFF)};
+    }
+}
+
+// Usage
+std::vector<std::byte> buffer(100);
+fill_pattern(buffer);      // Modify buffer
+print_hex_dump(buffer);    // Read buffer
+```
+
+### 2. Trivially Copyable Types as Byte Views
+
+Any trivially copyable type can be viewed as bytes:
+
+```cpp
+struct Point {
+    float x;
+    float y;
+};
+
+Point p{1.0f, 2.0f};
+byte_span view{std::span{&p, 1}};  // View Point's bytes
+```
+
+### 3. String Data Handling
+
+String data can be easily handled:
+
+```cpp
+std::string str = "Hello, World!";
+byte_span view{str};  // View string data as bytes
+
+// Convert to string_view
+auto sv = as_sv(view);  // Get as std::string_view
+```
+
+### 4. Implicit Conversion in Function Arguments
+
+Functions can accept various container types through implicit conversion:
+
+```cpp
+void process_bytes(byte_span view) {
+    // Process byte data
+}
+
+// Various ways to call
+std::vector<std::byte> vec(100);
+process_bytes(vec);  // OK
+
+std::array<char, 10> arr;
+process_bytes(arr);  // OK
+
+unsigned char raw_data[20];
+process_bytes(raw_data);  // OK
+```
+
+### 5. Data Type Conversions
+
+Safe data type conversions:
+
+```cpp
+std::vector<int> numbers = {1, 2, 3, 4};
+byte_span view{numbers};
+
+// Read as span of ints
+auto int_span = as_span<int>(view);
+// Get first value
+auto& first_int = as_value<int>(view);
+```
+
+### 6. Creating Sub-views
+
+Create views of specific ranges:
+
+```cpp
+std::vector<std::byte> data(100);
+byte_span view{data};
+
+auto first_10 = view.first(10);     // First 10 bytes
+auto last_10 = view.last(10);       // Last 10 bytes
+auto sub_view = view.subspan(5, 20); // 20 bytes starting at offset 5
+```
+
+## Requirements
+
+- C++20 or later
+- Compiler with concepts support
 
 # Building and installing
 
@@ -9,11 +175,3 @@ See the [BUILDING](BUILDING.md) document.
 # Contributing
 
 See the [CONTRIBUTING](CONTRIBUTING.md) document.
-
-# Licensing
-
-<!--
-Please go to https://choosealicense.com/licenses/ and choose a license that
-fits your needs. The recommended license for a project of this type is the
-Boost Software License 1.0.
--->