Add nitrobanner tool

This tool was made from reverse-engineering the Nitro SDK's makebanner,
and is intended to replace that program.

It has been tested to match the Diamond/Pearl banners as well as the
HeartGold/SoulSilver banners.

1 files changed, 22 insertions, 0 deletions

diff --git a/tools/nitrobanner/crc16.cpp b/tools/nitrobanner/crc16.cpp
new file mode 100644
index 00000000..bac64b57
--- /dev/null
+++ b/tools/nitrobanner/crc16.cpp
@@ -0,0 +1,22 @@
+#include <array>
+#include "banner.h"
+#include "crc16.h"
+
+u16 CalculateCRC16FromBannerData(const u8* banner_data) {
+    const std::array<u16, 16> crc_table = {
+        0x0000, 0xCC01, 0xD801, 0x1400,
+        0xF001, 0x3C00, 0x2800, 0xE401,
+        0xA001, 0x6C00, 0x7800, 0xB401,
+        0x5000, 0x9C01, 0x8801, 0x4400,
+    };
+
+    u16 checksum = 0xFFFF;
+
+    const std::size_t data_size = sizeof(Banner) - offsetof(Banner, bitmap);
+    for (std::size_t i = 0; i < data_size; i++) {
+        u16 lookup_index = crc_table[banner_data[i] & 0xF] ^ (checksum >> 4) ^ crc_table[checksum & 0xF];
+        checksum = crc_table[banner_data[i] >> 4] ^ (lookup_index >> 4) ^ crc_table[lookup_index & 0xF];
+    }
+
+    return checksum;
+}