From f32540fabce7d5dcb048d26919826c30dcb982b7 Mon Sep 17 00:00:00 2001
From: Lucy <lucy@cirno.systems>
Date: Thu, 14 Nov 2024 12:56:12 +0100
Subject: [PATCH] tool to fix the gba header's checksum

---
 bootfix.C | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 bootfix.C

diff --git a/bootfix.C b/bootfix.C
new file mode 100644
index 0000000..57448e8
--- /dev/null
+++ b/bootfix.C
@@ -0,0 +1,40 @@
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+int main(int argc, char** argv){
+	if(argc!=2){
+		fprintf(stderr, "missing argument");
+		return 1;
+	}
+	FILE* f = fopen(argv[1], "rb+");
+	if(f == NULL){
+		fprintf(stderr, "can't open dst file <%s>\n", argv[1]);
+		return 1;
+	}
+	uint8_t h[224] = {0};
+	fseek(f, 0, SEEK_END);
+	size_t s = ftell(f);
+	if(s!=sizeof(h)){
+		fprintf(stderr, "header is %zu but should be %zu", s, sizeof(h));
+		return 1;
+	}
+	rewind(f);
+	printf("reading\n");
+	fread(h, 1, sizeof(h), f);
+	printf("calculating header checksum..\n");
+	int8_t chk = 0;
+	for(int i=156;i<=184;i++){
+		chk += h[i];
+	}
+	uint8_t sum = -(0x19+chk);
+	h[185] = sum;
+	printf("checksum is %hhu\n", sum);
+	fseek(f, 0, SEEK_SET);
+	// write sum
+	fwrite(h, 1, sizeof(h), f);
+	fflush(f);
+	fclose(f);
+	return 0;
+}