Rationalise g_htoi() / xrdp_wm_htoi()

xrdp contains two functions which do similar things:-
- g_htoi() converts a hex string to an integer, ignoring unrecognised
  characters
- xrdp_wm_htoi() converts a hex string to an integer, ignoring leading
  whitespace, but terminating on unrecognised characters

An analysis of the uses of g_htoi() shows that the only place where
unrecognised characters might be encountered is parsing lines from
xrdp_keyboard.ini, where all values have an '0x' prefix (i.e. the 'x'
is unrecognised)

An analysis of xrdp_wm_htoi() shows that the functionality to ignore
leading whitespace is not used.

Both functions are replaced with a re-written g_htoi() which is const-
correct and provided with test cases. This function behaves in
the same way as the atoi() library function, in that it terminates on
an unexpected character.

The use of g_htoi() in parsing lines from xrdp_keyboard.ini is replaced
with a call to g_atoix() which handles the '0x' prefix correctly.

common/string_calls.c

@@ -502,82 +502,32 @@ size_t strlcpy(char *dst, const char *src, size_t dsize)
 #endif
 
 /*****************************************************************************/
-int
-g_htoi(char *str)
+unsigned int
+g_htoi(const char *str)
 {
-    int len;
-    int index;
-    int rv;
-    int val;
-    int shift;
-
-    rv = 0;
-    len = strlen(str);
-    index = len - 1;
-    shift = 0;
-
-    while (index >= 0)
+    unsigned int rv = 0;
+    while (*str != '\0')
     {
-        val = 0;
-
-        switch (str[index])
+        char c = *str;
+        unsigned int val;
+        if (c >= '0' && c <= '9')
         {
-            case '1':
-                val = 1;
-                break;
-            case '2':
-                val = 2;
-                break;
-            case '3':
-                val = 3;
-                break;
-            case '4':
-                val = 4;
-                break;
-            case '5':
-                val = 5;
-                break;
-            case '6':
-                val = 6;
-                break;
-            case '7':
-                val = 7;
-                break;
-            case '8':
-                val = 8;
-                break;
-            case '9':
-                val = 9;
-                break;
-            case 'a':
-            case 'A':
-                val = 10;
-                break;
-            case 'b':
-            case 'B':
-                val = 11;
-                break;
-            case 'c':
-            case 'C':
-                val = 12;
-                break;
-            case 'd':
-            case 'D':
-                val = 13;
-                break;
-            case 'e':
-            case 'E':
-                val = 14;
-                break;
-            case 'f':
-            case 'F':
-                val = 15;
-                break;
+            val = c - '0';
         }
-
-        rv = rv | (val << shift);
-        index--;
-        shift += 4;
+        else if (c >= 'A' && c <= 'F')
+        {
+            val = (c - 'A' + 10);
+        }
+        else if (c >= 'a' && c <= 'f')
+        {
+            val = (c - 'a' + 10);
+        }
+        else
+        {
+            break; // Unrecognised character
+        }
+        rv = (rv << 4) | val;
+        ++str;
     }
 
     return rv;

common/string_calls.h

@@ -310,7 +310,15 @@ size_t   strlcpy(char *dst, const char *src, size_t dsize);
  * @return int Integer expression of a string
  */
 int      g_atoix(const char *str);
-int      g_htoi(char *str);
+/**
+ * Converts a hex string to an integer
+ * @param str pointer to Hex string containing only hex digits
+ * @return value, converted from hex
+ *
+ * This function is intended to be used as an analogue to the standard
+ * function atoi(). It performs no error checking of its own
+ */
+unsigned int g_htoi(const char *str);
 int      g_bytes_to_hexstr(const void *bytes, int num_bytes, char *out_str,
                            int bytes_out_str);
 int      g_pos(const char *str, const char *to_find);