Implements custom tolower and toupper functions.

This commit implements custom equivalents for the C and C++ `tolower` and `toupper` Standard Library functions.
In addition it implements a utility function to capitalize the first letter of a string.

src/test/util_tests.cpp

@@ -1217,4 +1217,43 @@ BOOST_AUTO_TEST_CASE(test_DirIsWritable)
     fs::remove(tmpdirname);
 }
 
+BOOST_AUTO_TEST_CASE(test_ToLower)
+{
+    BOOST_CHECK_EQUAL(ToLower('@'), '@');
+    BOOST_CHECK_EQUAL(ToLower('A'), 'a');
+    BOOST_CHECK_EQUAL(ToLower('Z'), 'z');
+    BOOST_CHECK_EQUAL(ToLower('['), '[');
+    BOOST_CHECK_EQUAL(ToLower(0), 0);
+    BOOST_CHECK_EQUAL(ToLower(255), 255);
+
+    std::string testVector;
+    Downcase(testVector);
+    BOOST_CHECK_EQUAL(testVector, "");
+
+    testVector = "#HODL";
+    Downcase(testVector);
+    BOOST_CHECK_EQUAL(testVector, "#hodl");
+
+    testVector = "\x00\xfe\xff";
+    Downcase(testVector);
+    BOOST_CHECK_EQUAL(testVector, "\x00\xfe\xff");
+}
+
+BOOST_AUTO_TEST_CASE(test_ToUpper)
+{
+    BOOST_CHECK_EQUAL(ToUpper('`'), '`');
+    BOOST_CHECK_EQUAL(ToUpper('a'), 'A');
+    BOOST_CHECK_EQUAL(ToUpper('z'), 'Z');
+    BOOST_CHECK_EQUAL(ToUpper('{'), '{');
+    BOOST_CHECK_EQUAL(ToUpper(0), 0);
+    BOOST_CHECK_EQUAL(ToUpper(255), 255);
+}
+
+BOOST_AUTO_TEST_CASE(test_Capitalize)
+{
+    BOOST_CHECK_EQUAL(Capitalize(""), "");
+    BOOST_CHECK_EQUAL(Capitalize("bitcoin"), "Bitcoin");
+    BOOST_CHECK_EQUAL(Capitalize("\x00\xfe\xff"), "\x00\xfe\xff");
+}
+
 BOOST_AUTO_TEST_SUITE_END()

src/utilstrencodings.cpp

@@ -7,6 +7,7 @@
 
 #include <tinyformat.h>
 
+#include <algorithm>
 #include <cstdlib>
 #include <cstring>
 #include <errno.h>
@@ -584,3 +585,15 @@ bool ParseHDKeypath(const std::string& keypath_str, std::vector<uint32_t>& keypa
     }
     return true;
 }
+
+void Downcase(std::string& str)
+{
+    std::transform(str.begin(), str.end(), str.begin(), [](unsigned char c){return ToLower(c);});
+}
+
+std::string Capitalize(std::string str)
+{
+    if (str.empty()) return str;
+    str[0] = ToUpper(str.front());
+    return str;
+}

src/utilstrencodings.h

@@ -186,4 +186,48 @@ bool ConvertBits(const O& outfn, I it, I end) {
 /** Parse an HD keypaths like "m/7/0'/2000". */
 bool ParseHDKeypath(const std::string& keypath_str, std::vector<uint32_t>& keypath);
 
+/**
+ * Converts the given character to its lowercase equivalent.
+ * This function is locale independent. It only converts uppercase
+ * characters in the standard 7-bit ASCII range.
+ * @param[in] c     the character to convert to lowercase.
+ * @return          the lowercase equivalent of c; or the argument
+ *                  if no conversion is possible.
+ */
+constexpr unsigned char ToLower(unsigned char c)
+{
+    return (c >= 'A' && c <= 'Z' ? (c - 'A') + 'a' : c);
+}
+
+/**
+ * Converts the given string to its lowercase equivalent.
+ * This function is locale independent. It only converts uppercase
+ * characters in the standard 7-bit ASCII range.
+ * @param[in,out] str   the string to convert to lowercase.
+ */
+void Downcase(std::string& str);
+
+/**
+ * Converts the given character to its uppercase equivalent.
+ * This function is locale independent. It only converts lowercase
+ * characters in the standard 7-bit ASCII range.
+ * @param[in] c     the character to convert to uppercase.
+ * @return          the uppercase equivalent of c; or the argument
+ *                  if no conversion is possible.
+ */
+constexpr unsigned char ToUpper(unsigned char c)
+{
+    return (c >= 'a' && c <= 'z' ? (c - 'a') + 'A' : c);
+}
+
+/**
+ * Capitalizes the first character of the given string.
+ * This function is locale independent. It only capitalizes the
+ * first character of the argument if it has an uppercase equivalent
+ * in the standard 7-bit ASCII range.
+ * @param[in] str   the string to capitalize.
+ * @return          string with the first letter capitalized.
+ */
+std::string Capitalize(std::string str);
+
 #endif // BITCOIN_UTILSTRENCODINGS_H