From fb945457e6b8388a83321182b5ac67a654b69bbe Mon Sep 17 00:00:00 2001
From: Pin <wf6DJd8a3xSSCZbn@protonmail.com>
Date: Wed, 22 Sep 2021 22:10:39 -0400
Subject: [PATCH] wip

---
 .gitignore |  2 ++
 crc.c      | 42 ++++++++++++++++++++++++++++++++++++++----
 2 files changed, 40 insertions(+), 4 deletions(-)
 create mode 100644 .gitignore

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..dcfc80f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.png
+*.out
diff --git a/crc.c b/crc.c
index 06a74be..58df9c2 100644
--- a/crc.c
+++ b/crc.c
@@ -6,31 +6,65 @@
 int png_signature[8] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a };
 //int idat_signature[4] = { 0x, 0x, 0x, 0x}
 
-int CheckPNG(int *addr) {
+int check_header(int *addr) {
 	int signature_match = 0;
 	for( int i = 0; i < 8; i++ ) {
 		if (addr[i] != png_signature[i]) {
 			signature_match = 1;
 		}
 	}
-	printf("%d", signature_match);
+	printf("Sig Match: %d\n", signature_match);
 	return signature_match;
 
 }
 
+
+int check_header_length(int *addr, int offset) {
+	unsigned int res = 0;
+	for( int i = 0; i < 4; i++ ) {
+		res |= addr[offset+i];
+		if (i < 3) {
+			res <<= 8;
+		}
+	}
+	return res;
+}
+
+int first_idat(int *addr) {
+	int idat_found = 0;
+	int offset = 8;
+	int jump_offset = 0;
+	int header_type = 0;
+	while(idat_found == 0) {
+		jump_offset = check_header_length(addr, offset);
+		header_type = check_header_length(addr, offset+4);
+		printf("Jump: %d\n", jump_offset);
+		printf("Type: %d\n", header_type);
+		if(header_type == 1229209940) {
+			idat_found = 1;
+		} else {
+			offset = offset + jump_offset + 12;
+		}
+	}
+	return offset;
+}
+
 void main() {
 	FILE *fp;
 	int c;
 	int myArray[255] = {};
 	int i = 0;
+	int offset = 0;
 	fp = fopen("./1.png", "rt");
 	while((c = fgetc(fp)) != EOF) {
-		//printf("Value: %X\n", c);
 		myArray[i] = c;
 		i++;
 	}
 	fclose(fp);
-	CheckPNG(myArray);
+	//check_header(myArray);
+	//check_header_length(myArray, 54);
+	offset = first_idat(myArray);
+	printf("First Chunk: %d\n", offset);
 	//printf("%d\n", CheckPNG(myArray));
 	//int crcnum = crc(myArray, 19);
 	//printf("%08X\n", crcnum);