Add helper function for kernel normalization

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/kernel.c

@@ -121,4 +121,24 @@ void sum_kernel_preprocess(conv *map) {
 	}
 }
 
+/**
+ * Normalize a convolution kernel.
+ *
+ * @param[in,out] kern the kernel
+ */
+void normalize_conv_kern(conv *kern) {
+	double sum = 0.0;
+	for (int i = 0; i < kern->w * kern->h; i++) {
+		sum += kern->data[i];
+	}
+	double factor = 1.0 / sum;
+	for (int i = 0; i < kern->w * kern->h; i++) {
+		kern->data[i] *= factor;
+	}
+	if (kern->rsum) {
+		free(kern->rsum);
+		kern->rsum = NULL;
+	}
+}
+
 // vim: set noet sw=8 ts=8 :

src/kernel.h

@@ -25,6 +25,13 @@ conv *gaussian_kernel(double r);
 /// shadow_sum[x*d+y] is the sum of the kernel from (0, 0) to (x, y), inclusive
 void sum_kernel_preprocess(conv *map);
 
+/**
+ * Normalize a convolution kernel.
+ *
+ * @param[in,out] kern the kernel
+ */
+void normalize_conv_kern(conv *kern);
+
 static inline void free_conv(conv *k) {
 	free(k->rsum);
 	free(k);