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LibCrypto: Improve efficiency of UnsignedBigInteger::shift_left

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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
This commit is contained in:
Manuel Zahariev 2025-01-08 08:51:40 -08:00 • committed by Ali Mohammad Pur
parent 05cfbdd6fb
commit d2ea77c099
Notes: github-actions[bot] 2025-03-23 18:34:27 +00:00
9 changed files with 60 additions and 74 deletions
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6
Libraries/LibCrypto/BigInt/Algorithms/ModularPower.cpp
View file

@ -14,8 +14,6 @@ void UnsignedBigIntegerAlgorithms::destructive_modular_power_without_allocation(
UnsignedBigInteger& base,
UnsignedBigInteger const& m,
UnsignedBigInteger& temp_1,
UnsignedBigInteger& temp_2,
UnsignedBigInteger& temp_3,
UnsignedBigInteger& temp_multiply,
UnsignedBigInteger& temp_quotient,
UnsignedBigInteger& temp_remainder,
@ -25,7 +23,7 @@ void UnsignedBigIntegerAlgorithms::destructive_modular_power_without_allocation(
while (!(ep < 1)) {
if (ep.words()[0] % 2 == 1) {
// exp = (exp * base) % m;
multiply_without_allocation(exp, base, temp_1, temp_2, temp_3, temp_multiply);
multiply_without_allocation(exp, base, temp_1, temp_multiply);
divide_without_allocation(temp_multiply, m, temp_quotient, temp_remainder);
exp.set_to(temp_remainder);
}
@ -34,7 +32,7 @@ void UnsignedBigIntegerAlgorithms::destructive_modular_power_without_allocation(
ep.set_to(ep.shift_right(1));
// base = (base * base) % m;
multiply_without_allocation(base, base, temp_1, temp_2, temp_3, temp_multiply);
multiply_without_allocation(base, base, temp_1, temp_multiply);
divide_without_allocation(temp_multiply, m, temp_quotient, temp_remainder);
base.set_to(temp_remainder);