Spencer/PNG_CC
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2021-09-22 22:10:39 -04:00
parent 57cc8935de
commit fb945457e6
2 changed files with 40 additions and 4 deletions
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2
.gitignore vendored Normal file
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@@ -0,0 +1,2 @@
*.png
*.out

42
crc.c
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@@ -6,31 +6,65 @@
int png_signature[8] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a }; int png_signature[8] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a };
//int idat_signature[4] = { 0x, 0x, 0x, 0x} //int idat_signature[4] = { 0x, 0x, 0x, 0x}
int CheckPNG(int *addr) { int check_header(int *addr) {
int signature_match = 0; int signature_match = 0;
for( int i = 0; i < 8; i++ ) { for( int i = 0; i < 8; i++ ) {
if (addr[i] != png_signature[i]) { if (addr[i] != png_signature[i]) {
signature_match = 1; signature_match = 1;
} }
} }
printf("%d", signature_match); printf("Sig Match: %d\n", signature_match);
return 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() { void main() {
FILE *fp; FILE *fp;
int c; int c;
int myArray[255] = {}; int myArray[255] = {};
int i = 0; int i = 0;
int offset = 0;
fp = fopen("./1.png", "rt"); fp = fopen("./1.png", "rt");
while((c = fgetc(fp)) != EOF) { while((c = fgetc(fp)) != EOF) {
//printf("Value: %X\n", c);
myArray[i] = c; myArray[i] = c;
i++; i++;
} }
fclose(fp); 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)); //printf("%d\n", CheckPNG(myArray));
//int crcnum = crc(myArray, 19); //int crcnum = crc(myArray, 19);
//printf("%08X\n", crcnum); //printf("%08X\n", crcnum);