From f18ababe0d1db647d70e79733f0af409d721bf48 Mon Sep 17 00:00:00 2001
From: Project Nayuki <me@nayuki.io>
Date: Mon, 17 Apr 2017 18:02:14 +0000
Subject: [PATCH] Continued implementing C library by adding low-level QR Code
 get/set functions.

---
 c/qrcodegen.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 c/qrcodegen.h | 16 ++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/c/qrcodegen.c b/c/qrcodegen.c
index c7df95d..b5ddb82 100644
--- a/c/qrcodegen.c
+++ b/c/qrcodegen.c
@@ -30,6 +30,10 @@
 
 /*---- Forward declarations for private functions ----*/
 
+static bool getModule(const uint8_t qrcode[], int size, int x, int y);
+static void setModule(uint8_t qrcode[], int size, int x, int y, bool isBlack);
+static void setModuleBounded(uint8_t qrcode[], int size, int x, int y, bool isBlack);
+
 static void calcReedSolomonGenerator(int degree, uint8_t result[]);
 static void calcReedSolomonRemainder(const uint8_t data[], int dataLen, const uint8_t generator[], int degree, uint8_t result[]);
 static uint8_t finiteFieldMultiply(uint8_t x, uint8_t y);
@@ -73,6 +77,50 @@ bool qrcodegen_isNumeric(const char *text) {
 }
 
 
+// Public function - see documentation comment in header file.
+int qrcodegen_getSize(int version) {
+	assert(1 <= version && version <= 40);
+	return version * 4 + 17;
+}
+
+
+// Public function - see documentation comment in header file.
+bool qrcodegen_getModule(const uint8_t qrcode[], int version, int x, int y) {
+	int size = qrcodegen_getSize(version);
+	return (0 <= x && x < size && 0 <= y && y < size) && getModule(qrcode, size, x, y);
+}
+
+
+// Gets the module at the given coordinates, which must be in bounds.
+static bool getModule(const uint8_t qrcode[], int size, int x, int y) {
+	assert(21 <= size && size <= 177 && 0 <= x && x < size && 0 <= y && y < size);
+	int index = y * size + x;
+	int bitIndex = index & 7;
+	int byteIndex = index >> 3;
+	return ((qrcode[byteIndex] >> bitIndex) & 1) != 0;
+}
+
+
+// Sets the module at the given coordinates, which must be in bounds.
+static void setModule(uint8_t qrcode[], int size, int x, int y, bool isBlack) {
+	assert(21 <= size && size <= 177 && 0 <= x && x < size && 0 <= y && y < size);
+	int index = y * size + x;
+	int bitIndex = index & 7;
+	int byteIndex = index >> 3;
+	if (isBlack)
+		qrcode[byteIndex] |= 1 << bitIndex;
+	else
+		qrcode[byteIndex] &= (1 << bitIndex) ^ 0xFF;
+}
+
+
+// Sets the module at the given coordinates, doing nothing if out of bounds.
+static void setModuleBounded(uint8_t qrcode[], int size, int x, int y, bool isBlack) {
+	if (0 <= x && x < size && 0 <= y && y < size)
+		setModule(qrcode, size, x, y, isBlack);
+}
+
+
 // Calculates the Reed-Solomon generator polynomial of the given degree, storing in result[0 : degree].
 static void calcReedSolomonGenerator(int degree, uint8_t result[]) {
 	// Start with the monomial x^0
diff --git a/c/qrcodegen.h b/c/qrcodegen.h
index c85765f..1d6448c 100644
--- a/c/qrcodegen.h
+++ b/c/qrcodegen.h
@@ -37,3 +37,19 @@ bool qrcodegen_isAlphanumeric(const char *text);
  * Tests whether the given string can be encoded in numeric mode.
  */
 bool qrcodegen_isNumeric(const char *text);
+
+
+/* 
+ * Returns the side length of any QR Code of the given version.
+ * The version must be in the range [1, 40]. The result is in the range [21, 177].
+ * Note that the length of any QR Code byte buffer must be at least ceil(size^2 / 8).
+ */
+int qrcodegen_getSize(int version);
+
+
+/* 
+ * Returns the color of the module (pixel) at the given coordinates, which is either
+ * true for white or false for black. The top left corner has the coordinates (x=0, y=0).
+ * If the given coordinates are out of bounds, then false (white) is returned.
+ */
+bool qrcodegen_getModule(const uint8_t qrcode[], int version, int x, int y);