As it might be dangerous to use it.
This introduces `LTC_FAST_TYPE_{ASSIGN,MASK,XOR{2,3}}()` in order to
replace the potential unaligned loads.
This fixes the following UBSAN errors:
src/modes/ctr/ctr_encrypt.c:56:66: runtime error: load of misaligned address 0x7ffea07ee82f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/modes/ctr/ctr_encrypt.c:56:64: runtime error: store to misaligned address 0x7ffea07ee82f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:91: runtime error: load of misaligned address 0x7ffdd32f0d9f for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:52: runtime error: load of misaligned address 0x7ffdd32f0d71 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
tests/store_test.c:66:50: runtime error: store to misaligned address 0x7ffdd32f0dc1 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/pmac/pmac_process.c:40:50: runtime error: load of misaligned address 0x57c89c4329ec for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/xcbc/xcbc_process.c:35:60: runtime error: load of misaligned address 0x57c89c432ccc for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/mac/f9/f9_process.c:39:58: runtime error: load of misaligned address 0x5c2b1a1d2c14 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/encauth/gcm/gcm_process.c:82:58: runtime error: load of misaligned address 0x596b3e6aa354 for type 'LTC_FAST_TYPE', which requires 8 byte alignment
src/encauth/siv/siv.c:164:19: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:44:28: note: nonnull attribute specified here
src/misc/compare_testvector.c:63:25: runtime error: null pointer passed as argument 2, which is declared to never be null
/usr/include/string.h:65:33: note: nonnull attribute specified here
Running the `timing` demo with `LTC_MECC_FP` enabled gave a segfault,
which Valgrind narrowed down to
```
==135594== Invalid read of size 1
==135594== at 0x49298C: ss_accel_fp_mul2add (ltc_ecc_fp_mulmod.c:1007)
==135594== by 0x4931C1: ltc_ecc_fp_mul2add (ltc_ecc_fp_mulmod.c:1192)
==135594== by 0x41C1B2: ecc_verify_hash_internal (ecc_verify_hash_internal.c:114)
==135594== by 0x41C830: ecc_verify_hash_rfc7518_internal (ecc_verify_hash_rfc7518.c:35)
==135594== by 0x40340F: time_ecc (timing.c:1031)
==135594== by 0x402894: main (timing.c:1621)
==135594== Address 0x20feffeb2f is not stack'd, malloc'd or (recently) free'd
```
The origin being `ltc_mp_unsigned_bin_size(tkb)` returning 0, so y is -1,
but as an unsigned type that's no fun.
Fixed by making y a signed type.
Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>
