Implementation notes: amd64, titan0, crypto_sign/rainbow6440

Compiler output

rainbow_w-test.cpp: In file included from bqas.h:79,
rainbow_w-test.cpp:                  from rainbow_w.h:7,
rainbow_w-test.cpp:                  from rainbow_w-test.cpp:6:
rainbow_w-test.cpp: transpose8.h: In function 'void transpose8(__m128i*, const __m128i*)':
rainbow_w-test.cpp: transpose8.h:38:26: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                          ^
rainbow_w-test.cpp: transpose8.h:38:33: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                 ^
rainbow_w-test.cpp: transpose8.h:38:40: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                        ^
rainbow_w-test.cpp: transpose8.h:38:47: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                               ^
rainbow_w-test.cpp: transpose8.h:38:54: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                                      ^
rainbow_w-test.cpp: transpose8.h:38:61: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                                             ^
rainbow_w-test.cpp: transpose8.h:38:68: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
rainbow_w-test.cpp:    38 |         register __m128i a=s[0],b=s[1],c=s[2],d=s[3],e=s[4],f=s[5],g=s[6],h=s[7];
rainbow_w-test.cpp:       |                                                                    ^
rainbow_w-test.cpp: ...