Optimize some commonly used utf8 functions by:
- using counted loops instead of searching for terminating null. In
the important cases the caller already knows the length: change
the API to pass it in. Keep the old API version as well to avoid
extensive changes to non-critical debug and test code.
- ensure the common cases are at the start of if/then/else chains.
Usually 99+% of characters are ASCII even in mixed strings.
- for the "convert" functions, when both utf8 and utf16 lengths are
passed, and are equal, it means the entire string is ASCII, and a
specialized loop can be used. The compiler might then unroll or
even vectorize this.
The functions improved are (tested on Nexus 5 with a 44 character
ASCII string):
CountModifiedUtf8Chars : 20% faster
ConvertUtf16ToModifiedUtf8: 80% faster
ConvertModifiedUtf8ToUtf16: 200% faster
Also for completeness CountUtf8Bytes has been cleaned up a little, but
the speed is unchanged. Unlike CountModifiedUtf8Chars, it was already
passed the length, rather than searching for null.
Change-Id: I1c9b7dea3eda869fc9f5f6b4dd6be8cdd5bc3ac0
diff --git a/runtime/utf.h b/runtime/utf.h
index 1193d29..03158c4 100644
--- a/runtime/utf.h
+++ b/runtime/utf.h
@@ -40,6 +40,7 @@
* Returns the number of UTF-16 characters in the given modified UTF-8 string.
*/
size_t CountModifiedUtf8Chars(const char* utf8);
+size_t CountModifiedUtf8Chars(const char* utf8, size_t byte_count);
/*
* Returns the number of modified UTF-8 bytes needed to represent the given
@@ -51,6 +52,8 @@
* Convert from Modified UTF-8 to UTF-16.
*/
void ConvertModifiedUtf8ToUtf16(uint16_t* utf16_out, const char* utf8_in);
+void ConvertModifiedUtf8ToUtf16(uint16_t* utf16_out, size_t out_chars,
+ const char* utf8_in, size_t in_bytes);
/*
* Compare two modified UTF-8 strings as UTF-16 code point values in a non-locale sensitive manner
@@ -71,7 +74,8 @@
* this anyway, so if you want a NUL-terminated string, you know where to
* put the NUL byte.
*/
-void ConvertUtf16ToModifiedUtf8(char* utf8_out, const uint16_t* utf16_in, size_t char_count);
+void ConvertUtf16ToModifiedUtf8(char* utf8_out, size_t byte_count,
+ const uint16_t* utf16_in, size_t char_count);
/*
* The java.lang.String hashCode() algorithm.