C# strings use UTF-16 encoding where characters outside the basic multilingual plane require surrogate pairs, and lone surrogates create ill-formed strings that should be fixed before transmission. The author added ToWellFormed() and IsWellFormed() functions to the SimdUnicode library using SIMD instructions for fast validation and repair, achieving performance comparable to memory copies on modern processors.
C# strings use UTF-16 encoding where characters outside the basic multilingual plane require two 16-bit code units (surrogate pairs). The article describes fast SIMD-based algorithms in the SimdUnicode library to detect and fix ill-formed strings by replacing lone surrogates with the replacement character U+FFFD, achieving performance comparable to memory copying on modern processors.