This concept is rarely used in codebase and very much error-prone
if you forget to check it.
Instead, make it so that operations that would produce invalid integers
return an error instead.
Before:
- a separate Word element allocation of the underlying Vector<Word> was
necessary for every new word in a multi-word shift
- two additional temporary UnsignedBigInteger buffers were allocated
and passed through, including in downstream calls (e.g. Multiplication)
- an additional allocation and word shift for the carry
- FIXME note seems to point to some of these issues
After:
- main change is in LibCrypto/BigInt/Algorithms/BitwiseOperations.cpp
- one single allocation per call, using shift_left_by_n_words
- only the input "number" and "output" need to be allocated by the
caller
- downstream calls are adapted not to allocate or pass temporary
buffers
- noticeable performance improvement when running TestBigInteger:
0.41-0.42s (before) to 0.28-0.29s (after) Intel Core i9 laptop
Bonus: remove unused variables from UnsignedBigInteger::divided_by
- These were likely cut-and-paste artifacts from
UnsignedBigInteger::multiplied_by; not caught by "unused-varible".
NOTE: making this change in a separate commit than shift_right, even if
it touches the same file BitwiseOperations.cpp since:
- it is a "bonus" addition: not necessary for fixing the shift_right
bug, but logically unrelated to the shift_right code
- it brings a chain of downstream interface modifications (7 files),
unrelated to shift_right
- Before: UnsignedBigInteger::shift_right( n ) trigger index
verification error for n>31. An assumption of
num_bits<UnsignedBigInteger::BITS_IN_WORD was being made
- After: shift_right( n ) works correctly for n>31.
NOTE: "bonus" change; not necessary for fixing BigFraction::to_double
