Kernel: Add very simple PPM parser for Aarch64

This is much simpler and more embeddable version than libGFX one.
Solely purpose is to draw initial boot logo on screen before kernel
is even booted.

Kernel/Prekernel/Arch/aarch64/BootPPMParser.cpp

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2021, Marcin Undak <mcinek@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "BootPPMParser.h"
+
+namespace Prekernel {
+
+BootPPMParser::BootPPMParser(u8 const* buffer, u32 buffer_size)
+{
+    m_cursor = reinterpret_cast<char const*>(buffer);
+    m_buffer_end = m_cursor + buffer_size;
+}
+
+bool BootPPMParser::parse()
+{
+    if (!check_position()) {
+        return false;
+    }
+    if (!parse_magic()) {
+        return false;
+    }
+    if (!parse_new_line()) {
+        return false;
+    }
+    if (!parse_comment()) {
+        return false;
+    }
+    if (!parse_integer(image.width)) {
+        return false;
+    }
+    if (!parse_integer(image.height)) {
+        return false;
+    }
+    u32 max_color_value;
+    if (!parse_integer(max_color_value) || max_color_value != 255) {
+        return false;
+    }
+
+    image.pixel_data = reinterpret_cast<u8 const*>(m_cursor);
+
+    return true;
+}
+
+bool BootPPMParser::check_position() const
+{
+    if (m_cursor >= m_buffer_end) {
+        return false;
+    }
+    return true;
+}
+
+bool BootPPMParser::parse_magic()
+{
+    if (m_cursor[0] != 'P' || m_cursor[1] != '6') {
+        return false;
+    }
+    m_cursor += 2;
+
+    return check_position();
+}
+
+bool BootPPMParser::parse_new_line()
+{
+    if (*m_cursor != '\n') {
+        return false;
+    }
+    ++m_cursor;
+
+    return check_position();
+}
+
+bool BootPPMParser::parse_comment()
+{
+    if (*m_cursor == '#') {
+        // Skip to the next new line character
+        while (check_position() && *m_cursor != '\n') {
+            ++m_cursor;
+        }
+        ++m_cursor;
+    }
+
+    return check_position();
+}
+
+bool BootPPMParser::parse_integer(u32& value)
+{
+    auto begin = m_cursor;
+    while (check_position() && *m_cursor != ' ' && *m_cursor != '\n') {
+        ++m_cursor;
+    }
+    auto end = m_cursor;
+    ++m_cursor;
+
+    if (!check_position()) {
+        return false;
+    }
+
+    value = 0;
+    u32 multiplier = 1;
+    while (--end >= begin) {
+        value += multiplier * (*end - '0');
+        multiplier *= 10;
+    }
+
+    return true;
+}
+
+}