1 files changed, 113 insertions, 0 deletions
diff --git a/src/cmd/scat/dssread.c b/src/cmd/scat/dssread.c
new file mode 100644
index 00000000..06f0135e
--- /dev/null
+++ b/src/cmd/scat/dssread.c
@@ -0,0 +1,113 @@
+#include	<u.h>
+#include	<libc.h>
+#include	<bio.h>
+#include	"sky.h"
+
+static	void	dodecode(Biobuf*, Pix*, int, int, uchar*);
+static	long	getlong(uchar*);
+int	debug;
+
+Img*
+dssread(char *file)
+{
+	int nx, ny, scale, sumall;
+	Pix  *p, *pend;
+	uchar buf[21];
+	Biobuf *bp;
+	Img *ip;
+
+	if(debug)
+		Bprint(&bout, "reading %s\n", file);
+	bp = Bopen(file, OREAD);
+	if(bp == 0)
+		return 0;
+	if(Bread(bp, buf, sizeof(buf)) != sizeof(buf) ||
+	   buf[0] != 0xdd || buf[1] != 0x99){
+		werrstr("bad format");
+		return 0;
+	}
+	nx = getlong(buf+2);
+	ny = getlong(buf+6);
+	scale = getlong(buf+10);
+	sumall = getlong(buf+14);
+	if(debug)
+		fprint(2, "%s: nx=%d, ny=%d, scale=%d, sumall=%d, nbitplanes=%d,%d,%d\n",
+			file, nx, ny, scale, sumall, buf[18], buf[19], buf[20]);
+	ip = malloc(sizeof(Img) + (nx*ny-1)*sizeof(int));
+	if(ip == 0){
+		Bterm(bp);
+		werrstr("no memory");
+		return 0;
+	}
+	ip->nx = nx;
+	ip->ny = ny;
+	dodecode(bp, ip->a, nx, ny, buf+18);
+	ip->a[0] = sumall;	/* sum of all pixels */
+	Bterm(bp);
+	if(scale > 1){
+		p = ip->a;
+		pend = &ip->a[nx*ny];
+		while(p < pend)
+			*p++ *= scale;
+	}
+	hinv(ip->a, nx, ny);
+	return ip;
+}
+
+static
+void
+dodecode(Biobuf *infile, Pix  *a, int nx, int ny, uchar *nbitplanes)
+{
+	int nel, nx2, ny2, bits, mask;
+	Pix *aend, px;
+
+	nel = nx*ny;
+	nx2 = (nx+1)/2;
+	ny2 = (ny+1)/2;
+	memset(a, 0, nel*sizeof(*a));
+
+	/*
+	 * Initialize bit input
+	 */
+	start_inputing_bits();
+
+	/*
+	 * read bit planes for each quadrant
+	 */
+	qtree_decode(infile, &a[0],          ny, nx2,  ny2,  nbitplanes[0]);
+	qtree_decode(infile, &a[ny2],        ny, nx2,  ny/2, nbitplanes[1]);
+	qtree_decode(infile, &a[ny*nx2],     ny, nx/2, ny2,  nbitplanes[1]);
+	qtree_decode(infile, &a[ny*nx2+ny2], ny, nx/2, ny/2, nbitplanes[2]);
+
+	/*
+	 * make sure there is an EOF symbol (nybble=0) at end
+	 */
+	if(input_nybble(infile) != 0){
+		fprint(2, "dodecode: bad bit plane values\n");
+		exits("format");
+	}
+
+	/*
+	 * get the sign bits
+	 */
+	aend = &a[nel];
+	mask = 0;
+	bits = 0;;
+	for(; a<aend; a++) {
+		if(px = *a) {
+			if(mask == 0) {
+				mask = 0x80;
+				bits = Bgetc(infile);
+			}
+			if(mask & bits)
+				*a = -px;
+			mask >>= 1;
+		}
+	}
+}
+
+static
+long	getlong(uchar *p)
+{
+	return (p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3];
+}