JuliaLang/julia — pull request #7744 by catawbasam (2014-07-27 11:33:37+00:00)
Title: faster isvalid(SubString{UTF8String})

Faster isvalid(SubString{UTF8String}, i) based on specialized isvalid(UTF8String, i) in utf8.jl.
Speedup was roughly 2x in a small set of tests.