ucstrncmp: refactor with 32- and 8-byte loads

First of all, this removes the UB that used to try and calculate the
distance between the two strings. That's a valid technique in assembly,
but dangerous in C++ and totally unnecessary. The compiler is perfectly
able to generate loops with a single induction variable all on its own.

Second, this commit makes the main loop use 32-byte comparisons (16
characters at a time), which is a reasonable size for strings. We use
AVX2 if that's available, or an unrolled pair of 16-byte loads
otherwise. After the existing 16-byte comparison, this commit inserts an
8-byte (4-character) comparison and then reduces the final, unrolled
comparison to just 3 characters.

Change-Id: Ib48364abee9f464c96c6fffd152e474b39e1f293
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

0 files changed, 0 insertions, 0 deletions