Add str_startswith and str_endswith

Also add a couple of tests for both.

src/base/system.c

@@ -2392,6 +2392,30 @@ int str_comp_filenames(const char *a, const char *b)
 	return *a - *b;
 }
 
+const char *str_startswith(const char *str, const char *prefix)
+{
+	int prefixl = str_length(prefix);
+	if(str_comp_num(str, prefix, prefixl) == 0)
+	{
+		return str + prefixl;
+	}
+	else
+	{
+		return 0;
+	}
+}
+
+int str_endswith(const char *str, const char *suffix)
+{
+	int strl = str_length(str);
+	int suffixl = str_length(suffix);
+	if(strl < suffixl)
+	{
+		return 0;
+	}
+	return str_comp(str + strl - suffixl, suffix) == 0;
+}
+
 static int min3(int a, int b, int c)
 {
 	int min = a;

src/base/system.h

@@ -1187,6 +1187,40 @@ int str_comp_num(const char *a, const char *b, const int num);
 */
 int str_comp_filenames(const char *a, const char *b);
 
+/*
+	Function: str_startswith
+		Checks whether the string begins with a certain prefix.
+
+	Parameter:
+		str - String to check.
+		prefix - Prefix to look for.
+
+	Returns:
+		A pointer to the string str after the string prefix, or 0 if
+		the string prefix isn't a prefix of the string str.
+
+	Remarks:
+		- The strings are treated as zero-terminated strings.
+*/
+const char *str_startswith(const char *str, const char *prefix);
+
+/*
+	Function: str_endswith
+		Checks whether the string ends with a certain suffix.
+
+	Parameter:
+		str - String to check.
+		suffix - Suffix to look for.
+
+	Returns:
+		0 - String suffix is not a suffix of string str
+		1 - String suffix is a suffix of string str
+
+	Remarks:
+		- The strings are treated as zero-terminated strings.
+*/
+int str_endswith(const char *str, const char *suffix);
+
 /*
 	Function: str_utf8_dist
 		Computes the edit distance between two strings.

src/test/str.cpp

@@ -54,3 +54,37 @@ TEST(Str, Utf8CompConfusables)
 	EXPECT_FALSE(str_utf8_comp_confusable("o", "x") == 0);
 	EXPECT_TRUE(str_utf8_comp_confusable("aceiou", "ąçęįǫų") == 0);
 }
+
+TEST(Str, Startswith)
+{
+	EXPECT_TRUE(str_startswith("abcdef", "abc"));
+	EXPECT_FALSE(str_startswith("abc", "abcdef"));
+
+	EXPECT_TRUE(str_startswith("xyz", ""));
+	EXPECT_FALSE(str_startswith("", "xyz"));
+
+	EXPECT_FALSE(str_startswith("house", "home"));
+	EXPECT_FALSE(str_startswith("blackboard", "board"));
+
+	EXPECT_TRUE(str_startswith("поплавать", "по"));
+	EXPECT_FALSE(str_startswith("плавать", "по"));
+
+	static const char ABCDEF[] = "abcdef";
+	static const char ABC[] = "abc";
+	EXPECT_EQ(str_startswith(ABCDEF, ABC) - ABCDEF, str_length(ABC));
+}
+
+TEST(Str, Endswith)
+{
+	EXPECT_TRUE(str_endswith("abcdef", "def"));
+	EXPECT_FALSE(str_endswith("def", "abcdef"));
+
+	EXPECT_TRUE(str_endswith("xyz", ""));
+	EXPECT_FALSE(str_endswith("", "xyz"));
+
+	EXPECT_FALSE(str_endswith("rhyme", "mine"));
+	EXPECT_FALSE(str_endswith("blackboard", "black"));
+
+	EXPECT_TRUE(str_endswith("люди", "юди"));
+	EXPECT_FALSE(str_endswith("люди", "любовь"));
+}