Adds string to hex to format_utils. (#421)

src/utils/format_utils.cxx

@@ -35,6 +35,14 @@
 #include "utils/macros.h"
 #include "utils/format_utils.hxx"
 
+/// Translates a number 0..15 to a hex character.
+/// @param nibble input number
+/// @return character in 0-9a-f
+static char nibble_to_hex(unsigned nibble)
+{
+    return nibble <= 9 ? '0' + nibble : 'a' + (nibble - 10);
+}
+
 char* unsigned_integer_to_buffer_hex(unsigned int value, char* buffer)
 {
     int num_digits = 0;
@@ -50,16 +58,8 @@ char* unsigned_integer_to_buffer_hex(unsigned int value, char* buffer)
     do
     {
         HASSERT(num_digits >= 0);
-        unsigned int tmp2 = tmp % 16;
-        if (tmp2 <= 9)
-        {
-            buffer[num_digits--] = '0' + tmp2;
-        }
-        else
-        {
-            buffer[num_digits--] = 'a' + (tmp2 - 10);
-        }
-        tmp /= 16;
+        buffer[num_digits--] = nibble_to_hex(tmp & 0xf);
+        tmp >>= 4;
     } while (tmp);
     HASSERT(num_digits == -1);
     return ret;
@@ -80,16 +80,8 @@ char* uint64_integer_to_buffer_hex(uint64_t value, char* buffer)
     do
     {
         HASSERT(num_digits >= 0);
-        uint64_t tmp2 = tmp % 16;
-        if (tmp2 <= 9)
-        {
-            buffer[num_digits--] = '0' + tmp2;
-        }
-        else
-        {
-            buffer[num_digits--] = 'a' + (tmp2 - 10);
-        }
-        tmp /= 16;
+        buffer[num_digits--] = nibble_to_hex(tmp & 0xf);
+        tmp >>= 4;
     } while (tmp);
     HASSERT(num_digits == -1);
     return ret;
@@ -237,6 +229,19 @@ string int64_to_string_hex(int64_t value, unsigned padding)
     return ret;
 }
 
+string string_to_hex(const string &arg)
+{
+    string ret;
+    ret.reserve(arg.size() * 2);
+    for (char c : arg)
+    {
+        uint8_t cc = static_cast<uint8_t>(c);
+        ret.push_back(nibble_to_hex((cc >> 4) & 0xf));
+        ret.push_back(nibble_to_hex(cc & 0xf));
+    }
+    return ret;
+}
+
 string mac_to_string(uint8_t mac[6], bool colon)
 {
     string ret;

src/utils/format_utils.hxx

@@ -121,6 +121,12 @@ string uint64_to_string_hex(uint64_t value, unsigned padding = 0);
  */
 string int64_to_string_hex(int64_t value, unsigned padding = 0);
 
+/// Converts a (binary) string into a sequence of hex digits.
+/// @param arg input string
+/// @return string twice the length of arg with hex digits representing the
+/// original data.
+string string_to_hex(const string& arg);
+
 /// Formats a MAC address to string. Works both for Ethernet addresses as well
 /// as for OpenLCB node IDs.
 ///