From 5beb59e3b46b77251e19481bd5339decaf8f3df6 Mon Sep 17 00:00:00 2001
From: Claudio Felber <claudio.felber@perron2.ch>
Date: Mon, 21 Sep 2020 16:54:55 +0200
Subject: [PATCH] Support horizontally flipped QR-codes according to ISO
 18004:2015

---
 lib/decode.c | 16 ++++++++++++++++
 lib/quirc.h  |  3 +++
 2 files changed, 19 insertions(+)

diff --git a/lib/decode.c b/lib/decode.c
index 6266611..244ade3 100644
--- a/lib/decode.c
+++ b/lib/decode.c
@@ -916,3 +916,19 @@ quirc_decode_error_t quirc_decode(const struct quirc_code *code,
 
 	return QUIRC_SUCCESS;
 }
+
+void quirc_flip(struct quirc_code *code)
+{
+    struct quirc_code flipped;
+    memset(&flipped, 0, sizeof(flipped));
+    int offset = 0;
+    for (int y = 0, sx = 0; y < code->size; y++, sx++) {
+        for (int x = 0, sy = 0; x < code->size; x++, sy++) {
+            if (grid_bit(code, sx, sy)) {
+                flipped.cell_bitmap[offset >> 3] |= (1 << (offset & 7));
+            }
+            offset++;
+        }
+    }
+    memcpy(&code->cell_bitmap, &flipped.cell_bitmap, sizeof(flipped.cell_bitmap));
+}
\ No newline at end of file
diff --git a/lib/quirc.h b/lib/quirc.h
index 97b4bbe..d8d250d 100644
--- a/lib/quirc.h
+++ b/lib/quirc.h
@@ -168,6 +168,9 @@ void quirc_extract(const struct quirc *q, int index,
 quirc_decode_error_t quirc_decode(const struct quirc_code *code,
 				  struct quirc_data *data);
 
+/* Flip a QR-code according to optional mirror feature of ISO 18004:2015 */
+void quirc_flip(struct quirc_code *code);
+
 #ifdef __cplusplus
 }
 #endif