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/* Zgv v2.8 - GIF, JPEG and PBM/PGM/PPM viewer, for VGA PCs running Linux.
* Copyright (C) 1993-1996 Russell Marks. See README for license details.
*
* magic.c - Determines type of image file.
*/
#include <stdio.h>
#include <string.h>
#include "magic.h"
int magic_ident(char *filename)
{
FILE *in;
unsigned char buf[3];
if((in=fopen(filename,"rb"))==NULL)
return(_IS_BAD);
buf[0]=buf[1]=buf[2]=0;
fread(buf,1,3,in);
fclose(in);
/* We use the following rules:
* P?M files must have 'P', then a digit; '1'<=digit<='6'.
* GIF files must have "GIF"
* JPEG files must have first byte=0xff, second byte=0xd8 (M_SOI)
* BMP files must start with "BM"
* PCX files have 0x0A, version byte, then 0x01.
* mrf files must have "MRF"
* TGA files suck rocks ;-) (heuristics in this case)
*/
/* no magic for technical reasons - test for '.ngm' extension */
if(strlen(filename)>=4 && !strcasecmp(filename+strlen(filename)-4,".ngm"))
return(_IS_NGM);
/* xvpics look a bit like P?M files */
if(!strncmp(buf,"P7 ",3))
return(_IS_XVPIC);
/* PBM/PGM/PPM */
if(buf[0]=='P' && buf[1]>='1' && buf[1]<='6')
return(_IS_PNM);
/* GIF */
if(strncmp(buf,"GIF",3)==0)
return(_IS_GIF);
/* JPEG */
if(buf[0]==0xff && buf[1]==0xd8)
return(_IS_JPEG);
/* BMP */
if(buf[0]=='B' && buf[1]=='M')
return(_IS_BMP);
#ifdef PNG_SUPPORT
/* PNG */
if(buf[0]==0x89 && buf[1]=='P' && buf[2]=='N')
return(_IS_PNG); /* XXX should test the rest I s'pose */
#endif
/* PCX */
if(buf[0]==10 && buf[2]==1)
return(_IS_PCX);
/* mrf */
if(strncmp(buf,"MRF",3)==0)
return(_IS_MRF);
/* TGA */
/* this is hairy, since TGA files don't have a magic number.
* we make a guess based on some of the image info.
* (whether it has a colourmap or not, and the type)
*/
if((buf[1]==1 && (buf[2]==1 || buf[2]==9)) ||
(buf[1]<=1 && (buf[2]==2 || buf[2]==10)))
return(_IS_TGA);
/* if no valid header */
return(_IS_BAD);
}
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