Add function to convert a hex string to binary.

hex2bin.c

@@ -0,0 +1,60 @@
+/*
+ * This file is part of the DiscImageChef Remote Server.
+ * Copyright (c) 2019 Natalia Portillo.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <malloc.h>
+#include <stddef.h>
+#include <string.h>
+
+int hexchr2bin(const char hex, char* out)
+{
+    if(out == NULL) return 0;
+
+    if(hex >= '0' && hex <= '9')
+        *out = hex - '0';
+    else if(hex >= 'A' && hex <= 'F')
+        *out = hex - 'A' + 10;
+    else if(hex >= 'a' && hex <= 'f')
+        *out = hex - 'a' + 10;
+    else
+        return 0;
+
+    return 1;
+}
+
+size_t hexs2bin(const char* hex, unsigned char** out)
+{
+    size_t len;
+    char   b1;
+    char   b2;
+    size_t i;
+
+    if(hex == NULL || *hex == '\0' || out == NULL) return 0;
+
+    len = strlen(hex);
+    if(len % 2 != 0) return 0;
+    len /= 2;
+
+    *out = malloc(len);
+    memset(*out, 'A', len);
+    for(i = 0; i < len; i++)
+    {
+        if(!hexchr2bin(hex[i * 2], &b1) || !hexchr2bin(hex[i * 2 + 1], &b2)) return 0;
+
+        (*out)[i] = (b1 << 4) | b2;
+    }
+    return len;
+}