Add scat. Temporary fix to rc r.e. note groups.
diff --git a/src/cmd/scat/qtree.c b/src/cmd/scat/qtree.c
new file mode 100644
index 0000000..a3549c6
--- /dev/null
+++ b/src/cmd/scat/qtree.c
@@ -0,0 +1,278 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include "sky.h"
+
+static void qtree_expand(Biobuf*, uchar*, int, int, uchar*);
+static void qtree_copy(uchar*, int, int, uchar*, int);
+static void qtree_bitins(uchar*, int, int, Pix*, int, int);
+static void read_bdirect(Biobuf*, Pix*, int, int, int, uchar*, int);
+
+void
+qtree_decode(Biobuf *infile, Pix *a, int n, int nqx, int nqy, int nbitplanes)
+{
+ int log2n, k, bit, b, nqmax;
+ int nx,ny,nfx,nfy,c;
+ int nqx2, nqy2;
+ unsigned char *scratch;
+
+ /*
+ * log2n is log2 of max(nqx,nqy) rounded up to next power of 2
+ */
+ nqmax = nqy;
+ if(nqx > nqmax)
+ nqmax = nqx;
+ log2n = log(nqmax)/LN2+0.5;
+ if (nqmax > (1<<log2n))
+ log2n++;
+
+ /*
+ * allocate scratch array for working space
+ */
+ nqx2 = (nqx+1)/2;
+ nqy2 = (nqy+1)/2;
+ scratch = (uchar*)malloc(nqx2*nqy2);
+ if(scratch == nil) {
+ fprint(2, "qtree_decode: insufficient memory\n");
+ exits("memory");
+ }
+
+ /*
+ * now decode each bit plane, starting at the top
+ * A is assumed to be initialized to zero
+ */
+ for(bit = nbitplanes-1; bit >= 0; bit--) {
+ /*
+ * Was bitplane was quadtree-coded or written directly?
+ */
+ b = input_nybble(infile);
+ if(b == 0) {
+ /*
+ * bit map was written directly
+ */
+ read_bdirect(infile, a, n, nqx, nqy, scratch, bit);
+ } else
+ if(b != 0xf) {
+ fprint(2, "qtree_decode: bad format code %x\n",b);
+ exits("format");
+ } else {
+ /*
+ * bitmap was quadtree-coded, do log2n expansions
+ * read first code
+ */
+
+ scratch[0] = input_huffman(infile);
+
+ /*
+ * do log2n expansions, reading codes from file as necessary
+ */
+ nx = 1;
+ ny = 1;
+ nfx = nqx;
+ nfy = nqy;
+ c = 1<<log2n;
+ for(k = 1; k<log2n; k++) {
+ /*
+ * this somewhat cryptic code generates the sequence
+ * n[k-1] = (n[k]+1)/2 where n[log2n]=nqx or nqy
+ */
+ c = c>>1;
+ nx = nx<<1;
+ ny = ny<<1;
+ if(nfx <= c)
+ nx--;
+ else
+ nfx -= c;
+ if(nfy <= c)
+ ny--;
+ else
+ nfy -= c;
+ qtree_expand(infile, scratch, nx, ny, scratch);
+ }
+
+ /*
+ * copy last set of 4-bit codes to bitplane bit of array a
+ */
+ qtree_bitins(scratch, nqx, nqy, a, n, bit);
+ }
+ }
+ free(scratch);
+}
+
+/*
+ * do one quadtree expansion step on array a[(nqx+1)/2,(nqy+1)/2]
+ * results put into b[nqx,nqy] (which may be the same as a)
+ */
+static
+void
+qtree_expand(Biobuf *infile, uchar *a, int nx, int ny, uchar *b)
+{
+ uchar *b1;
+
+ /*
+ * first copy a to b, expanding each 4-bit value
+ */
+ qtree_copy(a, nx, ny, b, ny);
+
+ /*
+ * now read new 4-bit values into b for each non-zero element
+ */
+ b1 = &b[nx*ny];
+ while(b1 > b) {
+ b1--;
+ if(*b1 != 0)
+ *b1 = input_huffman(infile);
+ }
+}
+
+/*
+ * copy 4-bit values from a[(nx+1)/2,(ny+1)/2] to b[nx,ny], expanding
+ * each value to 2x2 pixels
+ * a,b may be same array
+ */
+static
+void
+qtree_copy(uchar *a, int nx, int ny, uchar *b, int n)
+{
+ int i, j, k, nx2, ny2;
+ int s00, s10;
+
+ /*
+ * first copy 4-bit values to b
+ * start at end in case a,b are same array
+ */
+ nx2 = (nx+1)/2;
+ ny2 = (ny+1)/2;
+ k = ny2*(nx2-1) + ny2-1; /* k is index of a[i,j] */
+ for (i = nx2-1; i >= 0; i--) {
+ s00 = 2*(n*i+ny2-1); /* s00 is index of b[2*i,2*j] */
+ for (j = ny2-1; j >= 0; j--) {
+ b[s00] = a[k];
+ k -= 1;
+ s00 -= 2;
+ }
+ }
+
+ /*
+ * now expand each 2x2 block
+ */
+ for(i = 0; i<nx-1; i += 2) {
+ s00 = n*i; /* s00 is index of b[i,j] */
+ s10 = s00+n; /* s10 is index of b[i+1,j] */
+ for(j = 0; j<ny-1; j += 2) {
+ b[s10+1] = b[s00] & 1;
+ b[s10 ] = (b[s00]>>1) & 1;
+ b[s00+1] = (b[s00]>>2) & 1;
+ b[s00 ] = (b[s00]>>3) & 1;
+ s00 += 2;
+ s10 += 2;
+ }
+ if(j < ny) {
+ /*
+ * row size is odd, do last element in row
+ * s00+1, s10+1 are off edge
+ */
+ b[s10 ] = (b[s00]>>1) & 1;
+ b[s00 ] = (b[s00]>>3) & 1;
+ }
+ }
+ if(i < nx) {
+ /*
+ * column size is odd, do last row
+ * s10, s10+1 are off edge
+ */
+ s00 = n*i;
+ for (j = 0; j<ny-1; j += 2) {
+ b[s00+1] = (b[s00]>>2) & 1;
+ b[s00 ] = (b[s00]>>3) & 1;
+ s00 += 2;
+ }
+ if(j < ny) {
+ /*
+ * both row and column size are odd, do corner element
+ * s00+1, s10, s10+1 are off edge
+ */
+ b[s00 ] = (b[s00]>>3) & 1;
+ }
+ }
+}
+
+/*
+ * Copy 4-bit values from a[(nx+1)/2,(ny+1)/2] to b[nx,ny], expanding
+ * each value to 2x2 pixels and inserting into bitplane BIT of B.
+ * A,B may NOT be same array (it wouldn't make sense to be inserting
+ * bits into the same array anyway.)
+ */
+static
+void
+qtree_bitins(uchar *a, int nx, int ny, Pix *b, int n, int bit)
+{
+ int i, j;
+ Pix *s00, *s10;
+ Pix px;
+
+ /*
+ * expand each 2x2 block
+ */
+ for(i=0; i<nx-1; i+=2) {
+ s00 = &b[n*i]; /* s00 is index of b[i,j] */
+ s10 = s00+n; /* s10 is index of b[i+1,j] */
+ for(j=0; j<ny-1; j+=2) {
+ px = *a++;
+ s10[1] |= ( px & 1) << bit;
+ s10[0] |= ((px>>1) & 1) << bit;
+ s00[1] |= ((px>>2) & 1) << bit;
+ s00[0] |= ((px>>3) & 1) << bit;
+ s00 += 2;
+ s10 += 2;
+ }
+ if(j < ny) {
+ /*
+ * row size is odd, do last element in row
+ * s00+1, s10+1 are off edge
+ */
+ px = *a++;
+ s10[0] |= ((px>>1) & 1) << bit;
+ s00[0] |= ((px>>3) & 1) << bit;
+ }
+ }
+ if(i < nx) {
+ /*
+ * column size is odd, do last row
+ * s10, s10+1 are off edge
+ */
+ s00 = &b[n*i];
+ for(j=0; j<ny-1; j+=2) {
+ px = *a++;
+ s00[1] |= ((px>>2) & 1) << bit;
+ s00[0] |= ((px>>3) & 1) << bit;
+ s00 += 2;
+ }
+ if(j < ny) {
+ /*
+ * both row and column size are odd, do corner element
+ * s00+1, s10, s10+1 are off edge
+ */
+ s00[0] |= ((*a>>3) & 1) << bit;
+ }
+ }
+}
+
+static
+void
+read_bdirect(Biobuf *infile, Pix *a, int n, int nqx, int nqy, uchar *scratch, int bit)
+{
+ int i;
+
+ /*
+ * read bit image packed 4 pixels/nybble
+ */
+ for(i = 0; i < ((nqx+1)/2) * ((nqy+1)/2); i++) {
+ scratch[i] = input_nybble(infile);
+ }
+
+ /*
+ * insert in bitplane BIT of image A
+ */
+ qtree_bitins(scratch, nqx, nqy, a, n, bit);
+}
