wip

Signed-off-by: Pin <wf6DJd8a3xSSCZbn@protonmail.com>

CRCLib.h

@@ -0,0 +1,51 @@
+/* Table of CRCs of all 8-bit messages. */
+unsigned long crc_table[256];
+   
+/* Flag: has the table been computed? Initially false. */
+int crc_table_computed = 0;
+   
+/* Make the table for a fast CRC. */
+void make_crc_table(void)
+{
+  unsigned long c;
+  int n, k;
+   
+  for (n = 0; n < 256; n++) {
+    c = (unsigned long) n;
+    for (k = 0; k < 8; k++) {
+      if (c & 1)
+        c = 0xedb88320L ^ (c >> 1);
+      else
+        c = c >> 1;
+    }
+    crc_table[n] = c;
+  }
+  crc_table_computed = 1;
+}
+  
+
+/* Update a running CRC with the bytes buf[0..len-1]--the CRC
+   should be initialized to all 1's, and the transmitted value
+   is the 1's complement of the final running CRC (see the
+   crc() routine below). */
+   
+unsigned long update_crc(unsigned long crc, unsigned char *buf,
+                         int len)
+{
+  unsigned long c = crc;
+  int n;
+   
+  if (!crc_table_computed)
+    make_crc_table();
+  for (n = 0; n < len; n++) {
+    c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
+  }
+  return c;
+}
+   
+/* Return the CRC of the bytes buf[0..len-1]. */
+unsigned long crc(unsigned char *buf, int len)
+{
+  return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
+}
+

crc.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include "CRCLib.h"
+
+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 signature_match = 0;
+	for( int i = 0; i < 8; i++ ) {
+		if (addr[i] != png_signature[i]) {
+			signature_match = 1;
+		}
+	}
+	printf("%d", signature_match);
+	return signature_match;
+
+}
+
+void main() {
+	FILE *fp;
+	int c;
+	int myArray[255] = {};
+	int i = 0;
+	fp = fopen("./1.png", "rt");
+	while((c = fgetc(fp)) != EOF) {
+		//printf("Value: %X\n", c);
+		myArray[i] = c;
+		i++;
+	}
+	fclose(fp);
+	CheckPNG(myArray);
+	//printf("%d\n", CheckPNG(myArray));
+	//int crcnum = crc(myArray, 19);
+	//printf("%08X\n", crcnum);
+}