1 files changed, 55 insertions, 0 deletions
diff --git a/libgamma_unhex_edid.c b/libgamma_unhex_edid.c
new file mode 100644
index 0000000..37c9681
--- /dev/null
+++ b/libgamma_unhex_edid.c
@@ -0,0 +1,55 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+/**
+ * Convert an hexadecimal representation of an EDID to a raw representation
+ * 
+ * @param   edid  The EDID in hexadecimal representation
+ * @return        The EDID in raw representation, it will be half the length
+ *                of `edid` (the input value); `NULL` on allocation error or
+ *                if the EDID is malformated, `errno` will be set accordingly
+ */
+unsigned char *
+libgamma_unhex_edid(const char *restrict edid)
+{
+	unsigned char *restrict out;
+	size_t i, n = strlen(edid);
+	char a, b;
+
+	/* Check that the length of the strings is even,
+	 * otherwise it cannot represent bytes */
+	if (n & 1) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	/* Allocate memory area for output octet array */
+	n /= 2 * sizeof(unsigned char);
+	out = malloc(n);
+	if (!out)
+		return NULL;
+
+	/* Convert to raw octet array */
+	for (i = 0; i < n; i++) {
+		/* Get the next character pair that, it represents an octet. */
+		a = edid[i * 2 + 0];
+		b = edid[i * 2 + 1];
+
+		/* Verify that the input is in hexadecimal */
+		if (!isxdigit(a) || !isxdigit(b)) {
+			free(out);
+			errno = EINVAL;
+			return NULL;
+		}
+
+		/* Convert each chararacter to raw format */
+		a = (char)((a & 15) + (a > '9' ? 9 : 0));
+		b = (char)((b & 15) + (b > '9' ? 9 : 0));
+
+		/* Combine the two characters into one octet */
+		out[i] = (unsigned char)((a << 4) | b);
+	}
+
+	return out;
+}