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
6 files changed