ref: fe1eb39db7ae6904924f3ab1f6f9b34416f2eb1b
dir: /sys/src/cmd/jpg/readtif.c/
/*
* code/documentation:
* http://partners.adobe.com/public/developer/en/tiff/TIFF6.pdf
* http://www.fileformat.info/format/tiff/egff.htm
* http://www.fileformat.info/mirror/egff/ch09_05.htm
* http://www.itu.int/rec/T-REC-T.4-199904-S/en
* http://www.itu.int/rec/T-REC-T.6-198811-I/en
*
* many thanks to paul bourke for a simple description of tiff:
* http://paulbourke.net/dataformats/tiff/
*
* copy-pasted fax codes and lzw help:
* http://www.remotesensing.org/libtiff/
*/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include <draw.h>
#include "imagefile.h"
enum {
II = 0x4949, /* little-endian */
MM = 0x4d4d, /* big-endian */
TIF = 0x002a /* tiff magic number */
};
enum {
Byte = 1,
Short = 3,
Long = 4
};
enum {
Width = 0x0100,
Length = 0x0101,
Bits = 0x0102,
Compression = 0x0103,
Nocomp = 0x0001,
Huffman = 0x0002,
T4enc = 0x0003,
T6enc = 0x0004,
Lzwenc = 0x0005,
Packbits = 0x8005,
Photometric = 0x0106,
Whitezero = 0x0000,
Blackzero = 0x0001,
Rgb = 0x0002,
Palette = 0x0003,
Fill = 0x010a,
Strips = 0x0111,
Orientation = 0x0112,
Samples = 0x0115,
Rows = 0x0116,
Counts = 0x0117,
Planar = 0x011c,
T4opts = 0x0124,
T6opts = 0x0125,
Predictor = 0x13d,
Color = 0x0140
};
enum {
Nfaxcodes = 10,
Nfaxtab = 105
};
enum {
Clrcode = 256,
Eoicode = 257,
Tabsz = 1<<12
};
typedef struct Tab Tab;
typedef struct Fax Fax;
typedef struct Code Code;
typedef struct Lzw Lzw;
typedef struct Fld Fld;
typedef struct Tif Tif;
struct Tab {
int len;
int code;
int run; /* run length */
};
struct Fax {
ulong n;
int m;
int st; /* state */
Tab *tab[2];
int ntab; /* position in tab */
Tab *eol;
int eolfill;
int (*getbit)(Fax *);
ulong *l1;
ulong *l2;
ulong nl;
uchar *data;
ulong next; /* next strip offset in data */
};
struct Code {
uchar val;
Code *next;
};
struct Lzw {
Code tab[Tabsz];
int ntab;
int len; /* code length */
ulong n;
int m;
uchar *data;
ulong next; /* next strip offset in data */
/* remaining allocated codes */
Code *first;
Code *last;
};
struct Fld {
uint tag;
uint typ;
ulong cnt;
ulong off; /* value offset */
ulong *val;
ulong nval;
};
struct Tif {
Biobuf *fd;
uint end; /* endianness */
uchar tmp[4];
uchar *buf;
ulong nbuf;
int eof; /* reached end of image */
ulong n; /* offset in buf array */
ulong off;
uint nfld;
Fld *fld;
ulong (*byte2)(uchar *);
ulong (*byte4)(uchar *);
/* field data */
ulong dx;
ulong dy;
ulong depth;
ulong comp;
uchar *(*uncompress)(Tif *);
ulong orientation;
ulong photo;
int (*decode)(Tif *, Rawimage *, uchar *);
ulong fill;
ulong *strips;
ulong nstrips;
ulong samples;
ulong rows;
ulong *counts;
ulong ncounts;
ulong planar;
ulong *color; /* color map */
ulong ncolor;
ulong t4;
ulong t6;
ulong predictor;
/* image data */
uchar *data;
ulong ndata;
};
/*
* imported from libdraw/arith.c to permit
* extern log2 function
*/
static int log2[] = {
-1, 0, 1, -1, 2, -1, -1, -1, 3,
-1, -1, -1, -1, -1, -1, -1, 4,
-1, -1, -1, -1, -1, -1, -1, 4 /* BUG */,
-1, -1, -1, -1, -1, -1, -1, 5
};
static Tab faxwhite[Nfaxtab] = {
{4, 0x7, 2}, /* 0111 */
{4, 0x8, 3}, /* 1000 */
{4, 0xb, 4}, /* 1011 */
{4, 0xc, 5}, /* 1100 */
{4, 0xe, 6}, /* 1110 */
{4, 0xf, 7}, /* 1111 */
{5, 0x12, 128}, /* 1001 0 */
{5, 0x13, 8}, /* 1001 1 */
{5, 0x14, 9}, /* 1010 0 */
{5, 0x1b, 64}, /* 1101 1 */
{5, 0x7, 10}, /* 0011 1 */
{5, 0x8, 11}, /* 0100 0 */
{6, 0x17, 192}, /* 0101 11 */
{6, 0x18, 1664}, /* 0110 00 */
{6, 0x2a, 16}, /* 1010 10 */
{6, 0x2b, 17}, /* 1010 11 */
{6, 0x3, 13}, /* 0000 11 */
{6, 0x34, 14}, /* 1101 00 */
{6, 0x35, 15}, /* 1101 01 */
{6, 0x7, 1}, /* 0001 11 */
{6, 0x8, 12}, /* 0010 00 */
{7, 0x13, 26}, /* 0010 011 */
{7, 0x17, 21}, /* 0010 111 */
{7, 0x18, 28}, /* 0011 000 */
{7, 0x24, 27}, /* 0100 100 */
{7, 0x27, 18}, /* 0100 111 */
{7, 0x28, 24}, /* 0101 000 */
{7, 0x2b, 25}, /* 0101 011 */
{7, 0x3, 22}, /* 0000 011 */
{7, 0x37, 256}, /* 0110 111 */
{7, 0x4, 23}, /* 0000 100 */
{7, 0x8, 20}, /* 0001 000 */
{7, 0xc, 19}, /* 0001 100 */
{8, 0x12, 33}, /* 0001 0010 */
{8, 0x13, 34}, /* 0001 0011 */
{8, 0x14, 35}, /* 0001 0100 */
{8, 0x15, 36}, /* 0001 0101 */
{8, 0x16, 37}, /* 0001 0110 */
{8, 0x17, 38}, /* 0001 0111 */
{8, 0x1a, 31}, /* 0001 1010 */
{8, 0x1b, 32}, /* 0001 1011 */
{8, 0x2, 29}, /* 0000 0010 */
{8, 0x24, 53}, /* 0010 0100 */
{8, 0x25, 54}, /* 0010 0101 */
{8, 0x28, 39}, /* 0010 1000 */
{8, 0x29, 40}, /* 0010 1001 */
{8, 0x2a, 41}, /* 0010 1010 */
{8, 0x2b, 42}, /* 0010 1011 */
{8, 0x2c, 43}, /* 0010 1100 */
{8, 0x2d, 44}, /* 0010 1101 */
{8, 0x3, 30}, /* 0000 0011 */
{8, 0x32, 61}, /* 0011 0010 */
{8, 0x33, 62}, /* 0011 0011 */
{8, 0x34, 63}, /* 0011 0100 */
{8, 0x35, 0}, /* 0011 0101 */
{8, 0x36, 320}, /* 0011 0110 */
{8, 0x37, 384}, /* 0011 0111 */
{8, 0x4, 45}, /* 0000 0100 */
{8, 0x4a, 59}, /* 0100 1010 */
{8, 0x4b, 60}, /* 0100 1011 */
{8, 0x5, 46}, /* 0000 0101 */
{8, 0x52, 49}, /* 0101 0010 */
{8, 0x53, 50}, /* 0101 0011 */
{8, 0x54, 51}, /* 0101 0100 */
{8, 0x55, 52}, /* 0101 0101 */
{8, 0x58, 55}, /* 0101 1000 */
{8, 0x59, 56}, /* 0101 1001 */
{8, 0x5a, 57}, /* 0101 1010 */
{8, 0x5b, 58}, /* 0101 1011 */
{8, 0x64, 448}, /* 0110 0100 */
{8, 0x65, 512}, /* 0110 0101 */
{8, 0x67, 640}, /* 0110 0111 */
{8, 0x68, 576}, /* 0110 1000 */
{8, 0xa, 47}, /* 0000 1010 */
{8, 0xb, 48}, /* 0000 1011 */
{9, 0x98, 1472}, /* 0100 1100 0 */
{9, 0x99, 1536}, /* 0100 1100 1 */
{9, 0x9a, 1600}, /* 0100 1101 0 */
{9, 0x9b, 1728}, /* 0100 1101 1 */
{9, 0xcc, 704}, /* 0110 0110 0 */
{9, 0xcd, 768}, /* 0110 0110 1 */
{9, 0xd2, 832}, /* 0110 1001 0 */
{9, 0xd3, 896}, /* 0110 1001 1 */
{9, 0xd4, 960}, /* 0110 1010 0 */
{9, 0xd5, 1024}, /* 0110 1010 1 */
{9, 0xd6, 1088}, /* 0110 1011 0 */
{9, 0xd7, 1152}, /* 0110 1011 1 */
{9, 0xd8, 1216}, /* 0110 1100 0 */
{9, 0xd9, 1280}, /* 0110 1100 1 */
{9, 0xda, 1344}, /* 0110 1101 0 */
{9, 0xdb, 1408}, /* 0110 1101 1 */
{11, 0x8, 1792}, /* 0000 0001 000 */
{11, 0xc, 1856}, /* 0000 0001 100 */
{11, 0xd, 1920}, /* 0000 0001 101 */
{12, 0x1, -1}, /* 0000 0000 0001 */
{12, 0x12, 1984}, /* 0000 0001 0010 */
{12, 0x13, 2048}, /* 0000 0001 0011 */
{12, 0x14, 2112}, /* 0000 0001 0100 */
{12, 0x15, 2176}, /* 0000 0001 0101 */
{12, 0x16, 2240}, /* 0000 0001 0110 */
{12, 0x17, 2304}, /* 0000 0001 0111 */
{12, 0x1c, 2368}, /* 0000 0001 1100 */
{12, 0x1d, 2432}, /* 0000 0001 1101 */
{12, 0x1e, 2496}, /* 0000 0001 1110 */
{12, 0x1f, 2560} /* 0000 0001 1111 */
};
static Tab faxblack[Nfaxtab] = {
{2, 0x2, 3}, /* 10 */
{2, 0x3, 2}, /* 11 */
{3, 0x2, 1}, /* 010 */
{3, 0x3, 4}, /* 011 */
{4, 0x2, 6}, /* 0010 */
{4, 0x3, 5}, /* 0011 */
{5, 0x3, 7}, /* 0001 1 */
{6, 0x4, 9}, /* 0001 00 */
{6, 0x5, 8}, /* 0001 01 */
{7, 0x4, 10}, /* 0000 100 */
{7, 0x5, 11}, /* 0000 101 */
{7, 0x7, 12}, /* 0000 111 */
{8, 0x4, 13}, /* 0000 0100 */
{8, 0x7, 14}, /* 0000 0111 */
{9, 0x18, 15}, /* 0000 1100 0 */
{10, 0x17, 16}, /* 0000 0101 11 */
{10, 0x18, 17}, /* 0000 0110 00 */
{10, 0x37, 0}, /* 0000 1101 11 */
{10, 0x8, 18}, /* 0000 0010 00 */
{10, 0xf, 64}, /* 0000 0011 11 */
{11, 0x17, 24}, /* 0000 0010 111 */
{11, 0x18, 25}, /* 0000 0011 000 */
{11, 0x28, 23}, /* 0000 0101 000 */
{11, 0x37, 22}, /* 0000 0110 111 */
{11, 0x67, 19}, /* 0000 1100 111 */
{11, 0x68, 20}, /* 0000 1101 000 */
{11, 0x6c, 21}, /* 0000 1101 100 */
{11, 0x8, 1792}, /* 0000 0001 000 */
{11, 0xc, 1856}, /* 0000 0001 100 */
{11, 0xd, 1920}, /* 0000 0001 101 */
{12, 0x1, -1}, /* 0000 0000 0001 */
{12, 0x12, 1984}, /* 0000 0001 0010 */
{12, 0x13, 2048}, /* 0000 0001 0011 */
{12, 0x14, 2112}, /* 0000 0001 0100 */
{12, 0x15, 2176}, /* 0000 0001 0101 */
{12, 0x16, 2240}, /* 0000 0001 0110 */
{12, 0x17, 2304}, /* 0000 0001 0111 */
{12, 0x1c, 2368}, /* 0000 0001 1100 */
{12, 0x1d, 2432}, /* 0000 0001 1101 */
{12, 0x1e, 2496}, /* 0000 0001 1110 */
{12, 0x1f, 2560}, /* 0000 0001 1111 */
{12, 0x24, 52}, /* 0000 0010 0100 */
{12, 0x27, 55}, /* 0000 0010 0111 */
{12, 0x28, 56}, /* 0000 0010 1000 */
{12, 0x2b, 59}, /* 0000 0010 1011 */
{12, 0x2c, 60}, /* 0000 0010 1100 */
{12, 0x33, 320}, /* 0000 0011 0011 */
{12, 0x34, 384}, /* 0000 0011 0100 */
{12, 0x35, 448}, /* 0000 0011 0101 */
{12, 0x37, 53}, /* 0000 0011 0111 */
{12, 0x38, 54}, /* 0000 0011 1000 */
{12, 0x52, 50}, /* 0000 0101 0010 */
{12, 0x53, 51}, /* 0000 0101 0011 */
{12, 0x54, 44}, /* 0000 0101 0100 */
{12, 0x55, 45}, /* 0000 0101 0101 */
{12, 0x56, 46}, /* 0000 0101 0110 */
{12, 0x57, 47}, /* 0000 0101 0111 */
{12, 0x58, 57}, /* 0000 0101 1000 */
{12, 0x59, 58}, /* 0000 0101 1001 */
{12, 0x5a, 61}, /* 0000 0101 1010 */
{12, 0x5b, 256}, /* 0000 0101 1011 */
{12, 0x64, 48}, /* 0000 0110 0100 */
{12, 0x65, 49}, /* 0000 0110 0101 */
{12, 0x66, 62}, /* 0000 0110 0110 */
{12, 0x67, 63}, /* 0000 0110 0111 */
{12, 0x68, 30}, /* 0000 0110 1000 */
{12, 0x69, 31}, /* 0000 0110 1001 */
{12, 0x6a, 32}, /* 0000 0110 1010 */
{12, 0x6b, 33}, /* 0000 0110 1011 */
{12, 0x6c, 40}, /* 0000 0110 1100 */
{12, 0x6d, 41}, /* 0000 0110 1101 */
{12, 0xc8, 128}, /* 0000 1100 1000 */
{12, 0xc9, 192}, /* 0000 1100 1001 */
{12, 0xca, 26}, /* 0000 1100 1010 */
{12, 0xcb, 27}, /* 0000 1100 1011 */
{12, 0xcc, 28}, /* 0000 1100 1100 */
{12, 0xcd, 29}, /* 0000 1100 1101 */
{12, 0xd2, 34}, /* 0000 1101 0010 */
{12, 0xd3, 35}, /* 0000 1101 0011 */
{12, 0xd4, 36}, /* 0000 1101 0100 */
{12, 0xd5, 37}, /* 0000 1101 0101 */
{12, 0xd6, 38}, /* 0000 1101 0110 */
{12, 0xd7, 39}, /* 0000 1101 0111 */
{12, 0xda, 42}, /* 0000 1101 1010 */
{12, 0xdb, 43}, /* 0000 1101 1011 */
{13, 0x4a, 640}, /* 0000 0010 0101 0 */
{13, 0x4b, 704}, /* 0000 0010 0101 1 */
{13, 0x4c, 768}, /* 0000 0010 0110 0 */
{13, 0x4d, 832}, /* 0000 0010 0110 1 */
{13, 0x52, 1280}, /* 0000 0010 1001 0 */
{13, 0x53, 1344}, /* 0000 0010 1001 1 */
{13, 0x54, 1408}, /* 0000 0010 1010 0 */
{13, 0x55, 1472}, /* 0000 0010 1010 1 */
{13, 0x5a, 1536}, /* 0000 0010 1101 0 */
{13, 0x5b, 1600}, /* 0000 0010 1101 1 */
{13, 0x64, 1664}, /* 0000 0011 0010 0 */
{13, 0x65, 1728}, /* 0000 0011 0010 1 */
{13, 0x6c, 512}, /* 0000 0011 0110 0 */
{13, 0x6d, 576}, /* 0000 0011 0110 1 */
{13, 0x72, 896}, /* 0000 0011 1001 0 */
{13, 0x73, 960}, /* 0000 0011 1001 1 */
{13, 0x74, 1024}, /* 0000 0011 1010 0 */
{13, 0x75, 1088}, /* 0000 0011 1010 1 */
{13, 0x76, 1152}, /* 0000 0011 1011 0 */
{13, 0x77, 1216} /* 0000 0011 1011 1 */
};
static Tab faxcodes[Nfaxcodes] = {
{1, 0x1, 0}, /* 1 */
{3, 0x1, 0}, /* 001 */
{3, 0x2, 0}, /* 010 */
{3, 0x3, 0}, /* 011 */
{4, 0x1, 0}, /* 0001 */
{6, 0x2, 0}, /* 0000 10 */
{6, 0x3, 0}, /* 0000 11 */
{7, 0x2, 0}, /* 0000 010 */
{7, 0x3, 0}, /* 0000 011 */
{12, 0x1, -1} /* 0000 0000 0001 */
};
static int typesizes[] = {0, 1, 0, 2, 4};
static int vcodeval[] = {0, 0, 0, 1, 0, 0, 2, 3};
static ulong byte2le(uchar *);
static ulong byte4le(uchar *);
static ulong byte2be(uchar *);
static ulong byte4be(uchar *);
static void readdata(Tif *, ulong);
static void readnbytes(Tif *, ulong);
static ulong readbyte(Tif *);
static ulong readshort(Tif *);
static ulong readlong(Tif *);
static int gototif(Tif *, ulong);
static int readheader(Tif *);
static uchar *nocomp(Tif *);
static int getbit1(Fax *);
static int getbit2(Fax *);
static Tab *findtab(Fax *, int, int, Tab *, int);
static Tab *gettab(Fax *, int);
static Tab *geteol(Fax *);
static int faxfill(Fax *, uchar *, ulong, ulong *, ulong *, ulong, int);
static void fillbits(Fax *);
static int faxalloclines(Fax *);
static Tab *getfax1d(Fax *, uchar *, ulong, ulong *, ulong *, ulong);
static Tab *getfax2d(Fax *, uchar *, ulong, ulong *, ulong *, ulong);
static int faxstrip(Tif *, Fax *, uchar *, ulong, ulong, ulong *);
static uchar *fax(Tif *);
static void tabinit(Lzw *);
static Code *newcode(Lzw *, Code *);
static void listadd(Lzw *, Code *);
static Code *tabadd(Lzw *, Code *, Code *);
static int getcode(Lzw *);
static int wstr(uchar *, ulong, ulong *, Code *, long *);
static void predict1(Tif *, uchar *);
static void predict8(Tif *, uchar *);
static int lzwstrip(Lzw *, uchar *, ulong, ulong *, long);
static uchar *lzw(Tif *);
static uchar *packbits(Tif *);
static int faxdecode(Tif *, Rawimage *, uchar *);
static int greydecode(Tif *, Rawimage *, uchar *);
static int rgbdecode(Tif *, Rawimage *, uchar *);
static int paldecode(Tif *, Rawimage *, uchar *);
static int parsefield(Tif *, Fld *);
static int readfield(Tif *, Fld *);
static int checkfields(Tif *);
static int readstrips(Tif *);
static Rawimage *decode(Tif *);
static void freefields(Tif *);
static Rawimage *readslave(Tif *);
static ulong
byte2le(uchar *buf)
{
return (buf[1] << 8) | buf[0];
}
static ulong
byte4le(uchar *buf)
{
return (byte2le(buf+2) << 16) | byte2le(buf);
}
static ulong
byte2be(uchar *buf)
{
return (buf[0] << 8) | buf[1];
}
static ulong
byte4be(uchar *buf)
{
return (byte2be(buf) << 16) | byte2be(buf+2);
}
static void
readdata(Tif *t, ulong offset)
{
long n, m;
ulong size;
if(offset < t->nbuf)
offset = t->nbuf;
m = offset + 4096 - t->nbuf;
size = (m + t->nbuf) * sizeof *t->buf;
if(t->buf == nil) {
if((t->buf = malloc(size)) == nil)
sysfatal("malloc: %r");
} else {
if((t->buf = realloc(t->buf, size)) == nil)
sysfatal("realloc: %r");
}
if((n = Bread(t->fd, t->buf+t->nbuf, m)) < 0)
sysfatal("Bread: %r");
if(n != m)
t->eof = 1;
t->nbuf += n;
}
static void
readnbytes(Tif *t, ulong n)
{
if(n <= 0 || n > 4)
sysfatal("cannot read %lud bytes", n);
if(t->n+n > t->nbuf) {
if(t->eof)
sysfatal("reached end of file");
readdata(t, 0);
}
memmove(t->tmp, t->buf+t->n, n);
t->n += n;
}
static ulong
readbyte(Tif *t)
{
readnbytes(t, 1);
return t->tmp[0];
}
static ulong
readshort(Tif *t)
{
readnbytes(t, 2);
return (*t->byte2)(t->tmp);
}
static ulong
readlong(Tif *t)
{
readnbytes(t, 4);
return (*t->byte4)(t->tmp);
}
static int
gototif(Tif *t, ulong n)
{
if(n < 8) {
werrstr("offset pointing to header");
return -1;
}
if(n > t->nbuf)
readdata(t, n);
t->n = n;
return 0;
}
static int
readheader(Tif *t)
{
uint n;
t->end = readshort(t);
switch(t->end) {
case II:
break;
case MM:
t->byte2 = byte2be;
t->byte4 = byte4be;
break;
default:
werrstr("illegal byte order: %#.4x", t->end);
return -1;
}
if((n = readshort(t)) != TIF) {
werrstr("illegal tiff magic: %#.4x", n);
return -1;
}
t->off = readlong(t);
return gototif(t, t->off);
}
static uchar *
nocomp(Tif *t)
{
return t->data;
}
static int
getbit1(Fax *f)
{
int bit;
if(f->n >= f->next)
return -1;
bit = (f->data[f->n] >> f->m) & 0x1;
f->m--;
if(f->m < 0) {
f->n++;
f->m = 7;
}
return bit;
}
static int
getbit2(Fax *f)
{
int bit;
if(f->n >= f->next)
return -1;
bit = (f->data[f->n] >> f->m) & 0x1;
f->m++;
if(f->m >= 8) {
f->n++;
f->m = 0;
}
return bit;
}
static Tab *
findtab(Fax *f, int code, int len, Tab *tab, int max)
{
Tab *p;
while(f->ntab < max) {
p = &tab[f->ntab];
if(p->len > len)
break;
if(p->code == code) {
f->ntab = 0;
return p;
}
f->ntab++;
}
return nil;
}
static Tab *
gettab(Fax *f, int mode)
{
int i, n, maxlen, bit, code;
Tab *p, *tab;
code = 0;
if(mode) {
n = Nfaxcodes;
tab = faxcodes;
} else {
n = Nfaxtab;
tab = f->tab[f->st];
}
maxlen = tab[n-1].len;
for(i = 1; i <= maxlen; i++) {
if((bit = (*f->getbit)(f)) < 0) {
f->st = -1;
return nil;
}
code = (code << 1) | bit;
if((p = findtab(f, code, i, tab, n)) != nil)
return p;
}
werrstr("code not found");
return nil;
}
static Tab *
geteol(Fax *f)
{
int i, bit;
Tab *p;
if(f->eol == nil) {
if(f->eolfill) {
for(i = 0; i < 4; i++) {
if((*f->getbit)(f) < 0) {
f->st = -1;
return nil;
}
}
}
if((p = gettab(f, 0)) == nil || p->run >= 0) {
werrstr("first eol");
return nil;
}
f->eol = p;
return p;
}
for(i = 0; (bit = (*f->getbit)(f)) == 0; i++)
;
if(bit < 0) {
f->st = -1;
return nil;
}
if(i < 11) {
werrstr("eol");
return nil;
}
return f->eol;
}
static int
faxfill(Fax *f, uchar *data, ulong size, ulong *i, ulong *x, ulong dx,
int n)
{
if((*x += n) > dx) {
werrstr("fax row overflow");
return -1;
}
if((*i += n) > size)
return -1;
if(f->st != 0)
memset(data+*i-n, f->st, n);
return 0;
}
static void
fillbits(Fax *f)
{
if(f->getbit == getbit1) {
if(f->m != 7) {
f->n++;
f->m = 7;
}
} else {
if(f->m != 0) {
f->n++;
f->m = 0;
}
}
}
static int
faxalloclines(Fax *f)
{
f->nl *= 2;
f->l1 = realloc(f->l1, f->nl*sizeof *f->l1);
if(f->l1 == nil)
return -1;
f->l2 = realloc(f->l2, f->nl*sizeof *f->l2);
if(f->l2 == nil) {
free(f->l1);
return -1;
}
return 0;
}
static Tab *
getfax1d(Fax *f, uchar *data, ulong size, ulong *i, ulong *x,
ulong dx)
{
int j, n;
Tab *p;
for(j = n = 0; *x < dx;) {
if((p = gettab(f, 0)) == nil)
return nil;
if((n = p->run) < 0) {
f->l1[j] = dx;
return f->eol;
}
if(faxfill(f, data, size, i, x, dx, n) < 0)
return nil;
if(n < 64) {
f->l1[j++] = *x;
f->st ^= 1;
}
if(j >= f->nl)
faxalloclines(f);
}
if(n >= 64) {
f->l1[j] = dx;
if((p = gettab(f, 0)) == nil)
return nil;
if((n = p->run) < 0)
return f->eol;
if(n != 0) {
werrstr("no terminating code");
return nil;
}
}
return nil;
}
static Tab *
getfax2d(Fax *f, uchar *data, ulong size, ulong *i, ulong *x,
ulong dx)
{
int j, k, n, code, len, v;
long a0, a1, b1, b2;
Tab *p;
a0 = -1;
for(j = 0; *x < dx;) {
for(k = 0;; k++) {
b1 = f->l1[k];
if(b1 > a0 && f->st == k%2)
break;
if(b1 >= dx)
break;
}
if((b2 = b1) < dx)
b2 = f->l1[k+1];
if((p = gettab(f, 1)) == nil)
return nil;
/* early eofb */
if(p->run < 0) {
f->st = -1;
return nil;
}
if(j+1 >= f->nl)
faxalloclines(f);
len = p->len;
code = p->code;
if(code == 1 && len == 3) {
/* horizontal */
for(k = 0; k < 2;) {
if((p = gettab(f, 0)) == nil)
return nil;
if((n = p->run) < 0) {
werrstr("2d eol");
return nil;
}
if(faxfill(f, data, size, i, x,
dx, n) < 0)
return nil;
if(n < 64) {
f->l2[j++] = *x;
f->st ^= 1;
k++;
}
}
} else if(code == 1 && len == 4) {
/* pass */
n = b2 - *x;
if(faxfill(f, data, size, i, x, dx, n) < 0)
return nil;
if(*x == dx)
f->l2[j++] = *x;
} else {
/* vertical */
switch(code) {
case 1:
case 2:
v = -vcodeval[len];
break;
case 3:
v = vcodeval[len];
break;
default:
werrstr("mode");
return nil;
}
a1 = b1 + v;
n = a1 - *x;
if(faxfill(f, data, size, i, x, dx, n) < 0)
return nil;
f->l2[j++] = *x;
f->st ^= 1;
}
a0 = *x;
}
memmove(f->l1, f->l2, j*sizeof *f->l1);
return nil;
}
static int
faxstrip(Tif *t, Fax *f, uchar *data, ulong size, ulong rows,
ulong *i)
{
int d1;
ulong x, y;
Tab *p;
d1 = t->comp != T6enc;
p = nil;
for(x = y = 0; x < t->dx || y < rows;) {
f->st = 0;
if(t->comp == T4enc) {
if(p == nil && geteol(f) == nil) {
if(f->st >= 0)
return -1;
break;
}
if(y > 0) {
*i += t->dx - x;
if(*i > size)
break;
}
if(t->t4 & 1) {
d1 = (*f->getbit)(f);
if(d1 < 0)
break;
}
}
x = 0;
y++;
if(d1) {
p = getfax1d(f, data, size, i,
&x, t->dx);
} else {
p = getfax2d(f, data, size, i,
&x, t->dx);
}
if(t->comp == Huffman)
fillbits(f);
if(p == nil && x != t->dx) {
if(f->st >= 0)
return -1;
if(x > t->dx)
return -1;
break;
}
}
if(*i > size) {
werrstr("fax data overflow");
return -1;
}
return 0;
}
/* i've encountered t4 images that did not have rtcs */
static uchar *
fax(Tif *t)
{
int m;
ulong i, j, datasz, r, dy;
uchar *data;
Fax f;
datasz = t->dx * t->dy * sizeof *data;
data = mallocz(datasz, 1);
f.nl = t->dx + 1;
f.l1 = mallocz(f.nl*sizeof *f.l1, 1);
f.l2 = mallocz(f.nl*sizeof *f.l2, 1);
if(data == nil || f.l1 == nil || f.l2 == nil) {
free(t->data);
if(data != nil)
free(data);
if(f.l1 != nil)
free(f.l1);
if(f.l2 != nil)
free(f.l2);
return nil;
}
if(t->fill == 1) {
f.getbit = getbit1;
m = 7;
} else {
f.getbit = getbit2;
m = 0;
}
f.tab[0] = faxwhite;
f.tab[1] = faxblack;
f.ntab = 0;
f.eol = nil;
if(t->comp == T4enc && t->t4 & (1<<1))
f.eolfill = 1;
else
f.eolfill = 0;
f.data = t->data;
for(i = j = 0, dy = t->dy; i < t->nstrips; i++) {
f.l1[0] = t->dx;
f.n = t->strips[i];
f.m = m;
if(i < t->nstrips-1)
f.next = t->strips[i+1];
else
f.next = t->ndata;
r = dy < t->rows? dy: t->rows;
if(faxstrip(t, &f, data, datasz, r, &j) < 0)
break;
dy -= t->rows;
}
if(i < t->nstrips) {
free(data);
data = nil;
}
free(t->data);
free(f.l1);
free(f.l2);
return data;
}
static void
tabinit(Lzw *l)
{
l->ntab = Eoicode + 1;
l->len = 9;
}
static Code *
newcode(Lzw *l, Code *p)
{
Code *q;
if(p == nil)
return nil;
if(l->first != nil) {
q = l->first;
if((l->first = l->first->next) == nil)
l->last = nil;
} else if((q = malloc(sizeof *q)) == nil)
return nil;
q->val = p->val;
q->next = nil;
return q;
}
static void
listadd(Lzw *l, Code *p)
{
if(p == nil)
return;
if(l->last != nil)
l->last->next = p;
else
l->first = l->last = p;
while(l->last->next != nil)
l->last = l->last->next;
}
static Code *
tabadd(Lzw *l, Code *p, Code *q)
{
Code *r, *s;
r = s = &l->tab[l->ntab];
switch(l->ntab) {
case 510:
case 1022:
case 2046:
l->len++;
break;
default:
break;
}
if(l->ntab++ >= Tabsz-3) {
werrstr("lzw table full");
return nil;
}
s->val = p->val;
while((p = p->next) != nil) {
if(s->next != nil)
s->next->val = p->val;
else if((s->next = newcode(l, p)) == nil)
return nil;
s = s->next;
}
if(s->next != nil) {
s->next->val = q->val;
s = s->next;
if(s->next != nil) {
listadd(l, s->next);
s->next = nil;
}
} else if((s->next = newcode(l, q)) == nil)
return nil;
return r;
}
static int
getcode(Lzw *l)
{
int i, c, code;
if(l->n >= l->next) {
eof:
werrstr("lzw eof");
return -1;
}
code = 0;
for(i = l->len-1; i >= 0; i--) {
c = (l->data[l->n] >> l->m) & 0x1;
code |= c << i;
l->m--;
if(l->m < 0) {
l->m = 7;
if(++l->n >= l->next && i > 0)
goto eof;
}
}
return code;
}
static int
wstr(uchar *data, ulong size, ulong *i, Code *p, long *striplen)
{
for(; p != nil; p = p->next, ++*i, --*striplen) {
if(*i >= size || *striplen < 0) {
werrstr("lzw overflow");
return -1;
}
data[*i] = p->val;
}
return 0;
}
static void
predict1(Tif *t, uchar *data)
{
int bpl, pix, b[8], d, m, n, j;
ulong x, y;
d = t->depth;
bpl = bytesperline(Rect(0, 0, t->dx, t->dy), d);
m = (1 << d) - 1;
n = 8 / d;
for(y = 0; y < t->dy; y++) {
for(x = 0; x < bpl; x++, data++) {
pix = *data;
b[n-1] = (pix >> d*(n-1)) & m;
if(x > 0)
b[n-1] += *(data-1) & m;
for(j = n-2; j >= 0; j--) {
b[j] = (pix >> d*j) & m;
b[j] += b[j+1];
}
for(j = pix = 0; j < n; j++)
pix |= (b[j] & m) << d*j;
*data = pix;
}
}
}
static void
predict8(Tif *t, uchar *data)
{
ulong j, s, x, y;
s = t->samples;
for(y = 0; y < t->dy; y++) {
for(x = 1, data += s; x < t->dx; x++) {
for(j = 0; j < s; j++, data++)
*data += *(data-s);
}
}
}
static int
lzwstrip(Lzw *l, uchar *data, ulong size, ulong *i, long striplen)
{
int c, oc;
Code *p, *q;
if((c = getcode(l)) != Clrcode) {
werrstr("clear code");
return -1;
}
for(oc = -1; c != Eoicode;) {
if(c < 0)
return -1;
if(c == Clrcode) {
if(oc >= 0)
tabinit(l);
if((c = getcode(l)) == Eoicode)
break;
if(c < 0)
return -1;
if(c >= l->ntab) {
werrstr("table overflow");
return -1;
}
if(wstr(data, size, i, &l->tab[c],
&striplen) < 0)
return -1;
} else if(c < l->ntab) {
p = &l->tab[c];
if(wstr(data, size, i, p,
&striplen) < 0)
return -1;
q = &l->tab[oc];
if(tabadd(l, q, p) == nil)
return -1;
} else if(c == l->ntab) {
q = &l->tab[oc];
if((p = tabadd(l, q, q)) == nil)
return -1;
if(wstr(data, size, i, p,
&striplen) < 0)
return -1;
} else {
werrstr("table overflow");
return -1;
}
if(striplen <= 0)
break;
oc = c;
c = getcode(l);
}
return 0;
}
static uchar *
lzw(Tif *t)
{
ulong i, j, size, r, dy;
long striplen;
uchar *data;
Lzw l;
Code *p, *q;
size = ((t->dx*t->dy*t->depth + 7) / 8) * sizeof *data;
if((data = malloc(size)) == nil) {
free(t->data);
return nil;
}
for(i = 0; i < Tabsz; i++) {
l.tab[i].val = i;
l.tab[i].next = nil;
}
l.data = t->data;
l.first = l.last = nil;
for(i = j = 0, dy = t->dy; i < t->nstrips; i++) {
tabinit(&l);
l.n = t->strips[i];
l.m = 7;
if(i < t->nstrips-1)
l.next = t->strips[i+1];
else
l.next = t->ndata;
r = dy < t->rows? dy: t->rows;
striplen = (t->dx*r*t->depth + 7) / 8;
if(lzwstrip(&l, data, size, &j, striplen) < 0)
break;
dy -= t->rows;
}
if(i < t->nstrips) {
free(data);
data = nil;
}
for(i = 0; i < Tabsz; i++) {
for(p = l.tab[i].next; (q = p) != nil;) {
p = p->next;
free(q);
}
}
for(p = l.first; (q = p) != nil;) {
p = p->next;
free(q);
}
free(t->data);
if(data != nil && t->predictor == 2) {
if(t->depth < 8)
predict1(t, data);
else
predict8(t, data);
}
return data;
}
static uchar *
packbits(Tif *t)
{
char n;
ulong i, j, k, size;
uchar *data;
size = ((t->dx*t->dy*t->depth + 7) / 8) * sizeof *data;
if((data = malloc(size)) == nil) {
free(t->data);
return nil;
}
for(i = 0, j = 0; i < t->ndata;) {
n = (char)t->data[i++];
if(n >= 0) {
k = n + 1;
if((j += k) > size || (i += k) > t->ndata)
break;
memmove(data+j-k, t->data+i-k, k);
} else if(n > -128 && n < 0) {
k = j - n + 1;
if(k > size || i >= t->ndata)
break;
for(; j < k; j++)
data[j] = t->data[i];
i++;
}
}
if(i < t->ndata) {
werrstr("packbits overflow");
free(data);
data = nil;
}
free(t->data);
return data;
}
static int
faxdecode(Tif *t, Rawimage *im, uchar *data)
{
ulong n;
for(n = 0; n < im->chanlen; n++) {
if(t->photo == Whitezero)
data[n] ^= 1;
im->chans[0][n] = data[n] * 0xff;
}
return 0;
}
static int
greydecode(Tif *t, Rawimage *im, uchar *data)
{
int pix, pmask, xmask;
ulong i, n, x, y;
pmask = (1 << t->depth) - 1;
xmask = 7 >> log2[t->depth];
for(y = 0, n = 0; y < t->dy; y++) {
i = y * bytesperline(im->r, t->depth);
for(x = 0; x < t->dx; x++, n++) {
if(n >= im->chanlen) {
werrstr("grey overflow");
return -1;
}
pix = (data[i] >> t->depth*((xmask -
x) & xmask)) & pmask;
if(((x + 1) & xmask) == 0)
i++;
if(t->photo == Whitezero)
pix ^= pmask;
pix = (pix * 0xff) / pmask;
im->chans[0][n] = pix;
}
}
return 0;
}
static int
rgbdecode(Tif *t, Rawimage *im, uchar *data)
{
ulong i, n, x, y;
for(y = 0, n = 0; y < t->dy; y++) {
for(x = 0; x < t->dx; x++, n += 3) {
if(n >= im->chanlen) {
werrstr("rgb overflow");
return -1;
}
i = (y*t->dx + x) * 3;
im->chans[0][n] = data[i+2];
im->chans[0][n+1] = data[i+1];
im->chans[0][n+2] = data[i];
}
}
return 0;
}
static int
paldecode(Tif *t, Rawimage *im, uchar *data)
{
int pix, pmask, xmask;
ulong i, n, x, y, *r, *g, *b, max;
pmask = (1 << t->depth) - 1;
xmask = 7 >> log2[t->depth];
for(i = 0, max = 1; i < t->ncolor; i++) {
if(t->color[i] > max)
max = t->color[i];
}
for(i = 0; i < t->ncolor; i++)
t->color[i] = (t->color[i] * 0xff) / max;
r = t->color;
g = r + pmask + 1;
b = g + pmask + 1;
for(y = 0, n = 0; y < t->dy; y++) {
i = y * bytesperline(im->r, t->depth);
for(x = 0; x < t->dx; x++, n += 3) {
if(n >= im->chanlen) {
werrstr("palette overflow");
return -1;
}
pix = (data[i] >> t->depth*((xmask -
x) & xmask)) & pmask;
if(((x + 1) & xmask) == 0)
i++;
im->chans[0][n] = b[pix];
im->chans[0][n+1] = g[pix];
im->chans[0][n+2] = r[pix];
}
}
return 0;
}
static int
parsefield(Tif *t, Fld *f)
{
ulong v;
v = f->val[0];
switch(f->tag) {
case Width:
t->dx = v;
break;
case Length:
t->dy = v;
break;
case Bits:
t->depth = v;
if(f->cnt == 3)
t->depth += f->val[1] + f->val[2];
break;
case Compression:
t->comp = v;
break;
case Photometric:
t->photo = v;
switch(t->photo) {
case Whitezero:
case Blackzero:
t->decode = greydecode;
break;
case Rgb:
t->decode = rgbdecode;
break;
case Palette:
t->decode = paldecode;
break;
default:
break;
}
break;
case Strips:
t->strips = f->val;
t->nstrips = f->cnt;
break;
case Fill:
t->fill = v;
break;
case Orientation:
t->orientation = v;
break;
case Samples:
t->samples = v;
break;
case Rows:
t->rows = v;
break;
case Counts:
t->counts = f->val;
t->ncounts = f->cnt;
break;
case Planar:
t->planar = v;
break;
case T4opts:
t->t4 = v;
break;
case T6opts:
t->t6 = v;
break;
case Predictor:
t->predictor = v;
break;
case Color:
t->color = f->val;
t->ncolor = f->cnt;
break;
default:
werrstr("shouldn't reach");
return -1;
}
return 0;
}
static int
readfield(Tif *t, Fld *f)
{
int size;
ulong i, j, n, off;
ulong (*readval)(Tif *);
f->tag = readshort(t);
f->typ = readshort(t);
f->cnt = readlong(t);
f->val = nil;
switch(f->tag) {
case Width:
case Length:
case Compression:
case Photometric:
case Fill:
case Orientation:
case Samples:
case Rows:
case Planar:
case T4opts:
case T6opts:
case Predictor:
if(f->cnt != 1) {
werrstr("field count");
return -1;
}
break;
case Bits:
if(f->cnt != 1 && f->cnt != 3) {
werrstr("field count");
return -1;
}
break;
case Strips:
case Counts:
case Color:
break;
default:
readlong(t);
return 0;
}
switch(f->typ) {
case Byte:
readval = readbyte;
break;
case Short:
readval = readshort;
break;
case Long:
readval = readlong;
break;
default:
werrstr("unsupported type\n");
return -1;
}
if((f->val = malloc(f->cnt*sizeof *f->val)) == nil)
return -1;
size = typesizes[f->typ];
if((n = size*f->cnt) <= 4) {
for(i = 0; i < f->cnt; i++)
f->val[i] = (*readval)(t);
f->off = 0x0;
f->nval = i;
for(j = n; j < 4; j += size)
(*readval)(t);
} else {
f->off = readlong(t);
off = t->n;
if(gototif(t, f->off) < 0)
return -1;
for(i = 0; i < f->cnt; i++)
f->val[i] = (*readval)(t);
f->nval = i;
if(gototif(t, off) < 0)
return -1;
}
return parsefield(t, f);
}
static int
checkfields(Tif *t)
{
ulong n, size;
if(t->dx == 0) {
werrstr("image width");
return -1;
}
if(t->dy == 0) {
werrstr("image length");
return -1;
}
switch(t->depth) {
case 1:
case 4:
case 8:
case 24:
break;
default:
werrstr("bits per sample");
return -1;
}
switch(t->comp) {
case Nocomp:
t->uncompress = nocomp;
break;
case Huffman:
case T4enc:
case T6enc:
t->uncompress = fax;
if(t->decode != nil)
t->decode = faxdecode;
if((t->comp == T4enc && t->t4 & (1<<1)) ||
(t->comp == T6enc &&
t->t6 & (1<<1))) {
werrstr("uncompressed mode");
return -1;
}
break;
case Lzwenc:
t->uncompress = lzw;
break;
case Packbits:
t->uncompress = packbits;
break;
default:
werrstr("compression");
return -1;
}
if(t->decode == nil) {
werrstr("photometric interpretation");
return -1;
}
if(t->depth > 1 && (t->comp == Huffman ||
t->comp == T4enc || t->comp == T6enc)) {
werrstr("compression");
return -1;
}
if(t->fill != 1 && t->fill != 2) {
werrstr("fill order");
return -1;
}
if(t->fill == 2 && t->depth != 1) {
werrstr("depth should be 1 with fill order 2");
return -1;
}
if(t->orientation != 1) {
werrstr("orientation");
return -1;
}
if(t->rows == 0) {
werrstr("rows per strip");
return -1;
}
n = (t->dy + t->rows - 1) / t->rows;
if(t->strips == nil || t->nstrips != n) {
werrstr("strip offsets");
return -1;
}
if(t->samples == 1 && t->photo == Rgb) {
werrstr("not enough samples per pixel");
return -1;
}
if(t->samples == 3 && t->photo != Rgb) {
werrstr("too many samples per pixel");
return -1;
}
if(t->samples != 1 && t->samples != 3) {
werrstr("samples per pixel");
return -1;
}
/*
* strip byte counts should not be missing,
* but we can guess correctly in this case
*/
size = sizeof *t->counts;
if(t->counts == nil && t->comp == Nocomp &&
t->nstrips == 1 &&
(t->counts = malloc(size)) != nil) {
t->counts[0] = (t->dx*t->dy*t->depth + 7) / 8;
t->ncounts = t->nstrips;
}
if(t->counts == nil || t->ncounts != t->nstrips) {
werrstr("strip byte counts");
return -1;
}
if(t->planar != 1) {
werrstr("planar configuration");
return -1;
}
if(t->photo == Palette && (t->color == nil ||
t->ncolor != 3*(1<<t->depth))) {
werrstr("color map");
return -1;
}
return 0;
}
static int
readstrips(Tif *t)
{
int i, j, n;
ulong off;
t->data = nil;
t->ndata = 0;
for(i = 0; i < t->nstrips; i++)
t->ndata += t->counts[i];
if(t->ndata == 0) {
werrstr("no image data");
return -1;
}
if((t->data = malloc(t->ndata*sizeof *t->data)) == nil)
return -1;
off = t->n;
for(i = n = 0; i < t->nstrips; i++) {
if(gototif(t, t->strips[i]) < 0)
return -1;
/*
* we store each strip's offset in t->data
* in order to skip the final rtc or eofb
* during fax decoding. t->strips is used
* to save on memory allocation. these
* offsets are also used in lzw as a
* preventive measure.
*/
t->strips[i] = n;
for(j = 0; j < t->counts[i]; j++, n++)
t->data[n] = readbyte(t);
}
return gototif(t, off);
}
static Rawimage *
decode(Tif *t)
{
ulong size;
uchar *data;
Rawimage *im;
if((im = malloc(sizeof *im)) == nil)
return nil;
im->r = Rect(0, 0, t->dx, t->dy);
im->cmap = nil;
im->cmaplen = 0;
im->chanlen = t->dx * t->dy;
if(t->photo == Rgb || t->photo == Palette) {
im->chandesc = CRGB24;
im->chanlen *= 3;
} else
im->chandesc = CY;
im->nchans = 1;
size = im->chanlen * sizeof *im->chans[0];
if((im->chans[0] = malloc(size)) == nil)
return nil;
/* unused members */
im->fields = 0;
im->gifflags = 0;
im->gifdelay = 0;
im->giftrindex = 0;
im->gifloopcount = 1;
if((data = (*t->uncompress)(t)) == nil)
return nil;
if((*t->decode)(t, im, data) < 0) {
free(im->chans[0]);
free(im);
im = nil;
}
free(data);
return im;
}
static void
freefields(Tif *t)
{
uint i;
for(i = 0; i < t->nfld; i++) {
if(t->fld[i].val != nil)
free(t->fld[i].val);
}
free(t->fld);
}
static Rawimage *
readslave(Tif *t)
{
uint i, j;
Rawimage *r;
if(readheader(t) < 0)
return nil;
if((t->nfld = readshort(t)) <= 0) {
werrstr("illegal field number: %#.4x", t->nfld);
return nil;
}
if((t->fld = malloc(t->nfld*sizeof *t->fld)) == nil)
return nil;
for(i = 0; i < t->nfld; i++) {
if(readfield(t, &t->fld[i]) < 0) {
if(t->fld[i].val != nil)
free(t->fld[i].val);
break;
}
}
if(i < t->nfld) {
for(j = 0; j < i; j++) {
if(t->fld[j].val != nil)
free(t->fld[j].val);
}
free(t->fld);
return nil;
}
readlong(t);
if(checkfields(t) < 0) {
freefields(t);
return nil;
}
if(readstrips(t) < 0) {
freefields(t);
if(t->data != nil)
free(t->data);
return nil;
}
free(t->buf);
r = decode(t);
freefields(t);
return r;
}
Rawimage **
Breadtif(Biobuf *b, int colorspace)
{
Rawimage **array, *r;
Tif *t;
if(colorspace != CRGB24) {
werrstr("unknown color space: %d",
colorspace);
return nil;
}
if((t = malloc(sizeof *t)) == nil)
return nil;
if((array = malloc(2*sizeof *array)) == nil)
return nil;
t->fd = b;
t->buf = nil;
t->nbuf = t->eof = t->n = 0;
/* order doesn't matter for the first two bytes */
t->byte2 = byte2le;
t->byte4 = byte4le;
/* defaults */
t->dx = 0;
t->dy = 0;
t->depth = 1;
t->comp = 1;
t->uncompress = nil;
t->photo = 0;
t->decode = nil;
t->fill = 1;
t->orientation = 1;
t->strips = nil;
t->nstrips = 0;
t->samples = 1;
t->rows = 0xffffffff; /* entire image is one strip */
t->counts = nil;
t->ncounts = 0;
t->planar = 1;
t->t4 = 0;
t->t6 = 0;
t->predictor = 1;
t->color = nil;
t->ncolor = 0;
r = readslave(t);
free(t);
array[0] = r;
array[1] = nil;
return array;
}
Rawimage **
readtif(int fd, int colorspace)
{
Rawimage **a;
Biobuf b;
if(Binit(&b, fd, OREAD) < 0)
return nil;
a = Breadtif(&b, colorspace);
Bterm(&b);
return a;
}