jpegsize.c

/**
 * The Codes wrote by tom7@cs.cmu.edu
 * I found it at http://carnage-melon.tom7.org/stuff/jpegsize.c
 */
#include <stdio.h>
/* portions derived from IJG code */

#define readbyte(a,b) do if(((a)=getc((b))) == EOF) return 0; while (0)
#define readword(a,b) do { int cc_=0,dd_=0; \
                          if((cc_=getc((b))) == EOF \
        		  || (dd_=getc((b))) == EOF) return 0; \
                          (a) = (cc_<<8) + (dd_); \
                          } while(0)


int scanhead (FILE * infile, int * image_width, int * image_height) {
	int marker=0;
	int dummy=0;
	if ( getc(infile) != 0xFF || getc(infile) != 0xD8 ) {
		return 0;
	}

	for (;;) {
    	int discarded_bytes=0;
		readbyte(marker,infile);
		while (marker != 0xFF) {
			discarded_bytes++;
			readbyte(marker,infile);
		}
		do readbyte(marker,infile); while (marker == 0xFF);
		if (discarded_bytes != 0) return 0;
 
		switch (marker) {
			case 0xC0:
			case 0xC1:
			case 0xC2:
			case 0xC3:
			case 0xC5:
			case 0xC6:
			case 0xC7:
			case 0xC9:
			case 0xCA:
			case 0xCB:
			case 0xCD:
			case 0xCE:
			case 0xCF: {
				readword(dummy,infile);	/* usual parameter length count */
				readbyte(dummy,infile);
				readword((*image_height),infile);
				readword((*image_width),infile);
				readbyte(dummy,infile);
				return 1;
				break;
			}
			case 0xDA:
			case 0xD9:
				return 0;
			default: {
				int length;
				readword(length,infile);

				if (length < 2)
					return 0;
				length -= 2;
				while (length > 0) {
					readbyte(dummy, infile);
					length--;
				} // end of while
			} // end of default
			break;
		} // end of switch
	} // end of for
} // end of scanhead