Add concat function to ustring and Strutil

src/include/OpenImageIO/strutil.h

@@ -448,6 +448,12 @@ std::string join (const Sequence& seq, string_view sep /*= ""*/, size_t len)
     return out.str();
 }
 
+/// Concatenate two strings, returning a std::string, implemented carefully
+/// to not perform any redundant copies or allocations. This is
+/// semantically equivalent to `Strutil::sprintf("%s%s", s, t)`, but is
+/// more efficient.
+std::string OIIO_API concat(string_view s, string_view t);
+
 /// Repeat a string formed by concatenating str n times.
 std::string OIIO_API repeat (string_view str, int n);
 

src/include/OpenImageIO/ustring.h

@@ -665,6 +665,12 @@ class OIIO_API ustring {
         return ustring(Strutil::format(fmt, args...));
     }
 
+    /// Concatenate two strings, returning a ustring, implemented carefully
+    /// to not perform any redundant copies or allocations. This is
+    /// semantically equivalent to `ustring::sprintf("%s%s", s, t)`, but is
+    /// more efficient.
+    static ustring concat(string_view s, string_view t);
+
     /// Generic stream output of a ustring.
     friend std::ostream& operator<<(std::ostream& out, const ustring& str)
     {

src/libutil/strutil.cpp

@@ -614,13 +614,41 @@ Strutil::split(string_view str, std::vector<string_view>& result,
 
 
 
+std::string
+Strutil::concat(string_view s, string_view t)
+{
+    size_t sl  = s.size();
+    size_t tl  = t.size();
+    size_t len = sl + tl;
+    std::unique_ptr<char[]> heap_buf;
+    char local_buf[256];
+    char* buf = local_buf;
+    if (len > sizeof(local_buf)) {
+        heap_buf.reset(new char[len]);
+        buf = heap_buf.get();
+    }
+    memcpy(buf, s.data(), sl);
+    memcpy(buf + sl, t.data(), tl);
+    return std::string(buf, len);
+}
+
+
+
 std::string
 Strutil::repeat(string_view str, int n)
 {
-    std::ostringstream out;
-    while (n-- > 0)
-        out << str;
-    return out.str();
+    size_t sl  = str.size();
+    size_t len = sl * std::max(0, n);
+    std::unique_ptr<char[]> heap_buf;
+    char local_buf[256];
+    char* buf = local_buf;
+    if (len > sizeof(local_buf)) {
+        heap_buf.reset(new char[len]);
+        buf = heap_buf.get();
+    }
+    for (int i = 0; i < n; ++i)
+        memcpy(buf + i * sl, str.data(), sl);
+    return std::string(buf, len);
 }
 
 

src/libutil/strutil_test.cpp

@@ -414,6 +414,21 @@ test_join()
 
 
 
+void
+test_concat()
+{
+    std::cout << "Testing concat\n";
+    OIIO_CHECK_EQUAL(Strutil::concat("foo", "bar"), "foobar");
+    OIIO_CHECK_EQUAL(Strutil::concat("foo", ""), "foo");
+    OIIO_CHECK_EQUAL(Strutil::concat("", "foo"), "foo");
+    OIIO_CHECK_EQUAL(Strutil::concat("", ""), "");
+    std::string longstring(Strutil::repeat("01234567890", 100));
+    OIIO_CHECK_EQUAL(Strutil::concat(longstring, longstring),
+                     Strutil::sprintf("%s%s", longstring, longstring));
+}
+
+
+
 void
 test_repeat()
 {
@@ -422,6 +437,8 @@ test_repeat()
     OIIO_CHECK_EQUAL(Strutil::repeat("foo", 1), "foo");
     OIIO_CHECK_EQUAL(Strutil::repeat("foo", 0), "");
     OIIO_CHECK_EQUAL(Strutil::repeat("foo", -1), "");
+    OIIO_CHECK_EQUAL(Strutil::repeat("0123456789", 100),
+                     Strutil::repeat("01234567890123456789", 50));
 }
 
 
@@ -1045,6 +1062,7 @@ main(int /*argc*/, char* /*argv*/[])
     test_strip();
     test_split();
     test_join();
+    test_concat();
     test_repeat();
     test_replace();
     test_excise_string_after_head();

src/libutil/ustring.cpp

@@ -419,6 +419,28 @@ ustring::make_unique(string_view strref)
     return result ? result : table.insert(strref, hash);
 }
 
+
+
+ustring
+ustring::concat(string_view s, string_view t)
+{
+    size_t sl  = s.size();
+    size_t tl  = t.size();
+    size_t len = sl + tl;
+    std::unique_ptr<char[]> heap_buf;
+    char local_buf[256];
+    char* buf = local_buf;
+    if (len > sizeof(local_buf)) {
+        heap_buf.reset(new char[len]);
+        buf = heap_buf.get();
+    }
+    memcpy(buf, s.data(), sl);
+    memcpy(buf + sl, t.data(), tl);
+    return ustring(buf, len);
+}
+
+
+
 std::string
 ustring::getstats(bool verbose)
 {

src/libutil/ustring_test.cpp

@@ -90,6 +90,14 @@ main(int argc, char* argv[])
     OIIO_CHECK_ASSERT(ustring("bar") != ustring("foo"));
     ustring foo("foo");
     OIIO_CHECK_ASSERT(foo.string() == "foo");
+    ustring bar("bar");
+    OIIO_CHECK_EQUAL(ustring::concat(foo, bar), "foobar");
+    OIIO_CHECK_EQUAL(ustring::concat(foo, "bar"), "foobar");
+    OIIO_CHECK_EQUAL(ustring::concat(foo, ""), "foo");
+    OIIO_CHECK_EQUAL(ustring::concat("", foo), "foo");
+    ustring longstring(Strutil::repeat("01234567890", 100));
+    OIIO_CHECK_EQUAL(ustring::concat(longstring, longstring),
+                     ustring::sprintf("%s%s", longstring, longstring));
 
     const int nhw_threads = Sysutil::hardware_concurrency();
     std::cout << "hw threads = " << nhw_threads << "\n";