Buffer.write(text, "utf16le") zero-extended an ASCII run eight bytes per
step with shifts and masks in 64-bit words. Where the target has vector
unpacks (SSE2 on x86-64, NEON on AArch64) it now widens sixteen bytes
per step: one load, a test of the high bits, and two unpacked stores.
The word loop stays for the remaining bytes and for other targets. A
scanner that fills a Uint16Array of code units this way, as tsc-ts does
once per source file, spends about half as long in the copy.
Chris Tate
9fd5c8a73f