(partially) layout code

1 files changed, 125 insertions, 0 deletions

diff --git a/lpg/libqr/code-layout.c b/lpg/libqr/code-layout.c
new file mode 100644
index 0000000..228758a
--- /dev/null
+++ b/lpg/libqr/code-layout.c
@@ -0,0 +1,125 @@
+#include <limits.h>
+#include <stdlib.h>
+#include "code-common.h"
+#include "code-layout.h"
+
+struct qr_iterator {
+        struct qr_code * code;
+        int dim;
+        int column;
+        int row;
+        int up;
+        int mask;
+        unsigned char * p;
+};
+
+static int is_data_bit(const struct qr_iterator * i)
+{
+        if (i->row == 6 || i->column == 6) /* timing */
+                return 0;
+
+        if (i->column < 9 && i->row < 9) /* top-left */
+                return 0;
+
+        if (i->column >= i->dim - 8 && i->row < 9) /* top-right */
+                return 0;
+
+        if (i->column < 9 && i->row >= i->dim - 8) /* bottom-left */
+                return 0;
+
+        /* XXX: format data */
+        /* XXX: alignment pattern */
+
+        return 1;
+}
+
+static void set_pointer(struct qr_iterator * i)
+{
+        i->mask = 1 << (i->column % CHAR_BIT);
+        i->p = i->code->modules
+                + i->code->line_stride * i->row
+                + i->column / CHAR_BIT;
+}
+
+static void advance(struct qr_iterator * i)
+{
+        do {
+                /* This XOR is to account for the vertical strip of
+                 * timing bits in column 6 which displaces everything.
+                 */
+                if ((i->column < 6) ^ !(i->column % 2)) {
+                        /* Right-hand part or at left edge */
+                        i->column -= 1;
+                } else {
+                        /* Left-hand part */
+                        i->column += 1;
+
+                        if (( i->up && i->row == 0) ||
+                            (!i->up && i->row == i->dim - 1)) {
+                                /* Hit the top / bottom */
+                                i->column -= 2;
+                                i->up = !i->up;
+                        } else {
+                                i->row += i->up ? -1 : 1;
+                        }
+                }
+
+                if (i->column < 0)
+                        continue; /* don't go off left edge */
+
+                /* Check for one-past-end */
+                if (i->column == 0 && i->row >= i->dim - 8)
+                        break;
+
+        } while (!is_data_bit(i));
+
+        set_pointer(i);
+}
+
+struct qr_iterator * qr_layout_begin(struct qr_code * code)
+{
+        struct qr_iterator * i;
+
+        i = malloc(sizeof(*i));
+        if (i) {
+                i->dim = code_side_length(code->format);
+                i->code = code;
+                i->column = i->dim - 1;
+                i->row = i->dim - 1;
+                i->up = 1;
+                set_pointer(i);
+        }
+
+        return i;
+}
+
+void qr_layout_end(struct qr_iterator * i)
+{
+        free(i);
+}
+
+unsigned int qr_layout_read(struct qr_iterator * i)
+{
+        unsigned int x = 0;
+        int b;
+
+        for (b = 0; b < 8; ++b) {
+                x |= (*i->p & i->mask) ? 1 : 0;
+                advance(i);
+                x <<= 1;
+        }
+
+        return x;
+}
+
+void qr_layout_write(struct qr_iterator * i, unsigned int x)
+{
+        int b;
+
+        for (b = 0; b < 8; ++b) {
+                *i->p |= (x & 0x80) ? i->mask : 0;
+                advance(i);
+                x <<= 1;
+        }
+}
+