in SocketRocket/Internal/Utilities/SRSIMDHelpers.m [14:18]
static void SRMaskBytesManual(uint8_t *bytes, size_t length, uint8_t *maskKey) {
for (size_t i = 0; i < length; i++) {
bytes[i] = bytes[i] ^ maskKey[i % sizeof(uint32_t)];
}
}