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LibCrypto: Remove now unused temporary BigInt buffers

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Plus 1 drive-by division->shift optimization
This commit is contained in:
Hendiadyoin1
2024-03-18 20:33:44 +01:00
committed by Andrew Kaster
parent c96d44e9cf
commit 70cfa60f56
Notes: sideshowbarker 2024-07-17 16:23:55 +09:00 
Author: https://github.com/Hendiadyoin1
Commit: https://github.com/SerenityOS/serenity/commit/70cfa60f56
Pull-request: https://github.com/SerenityOS/serenity/pull/23619
Issue: https://github.com/SerenityOS/serenity/issues/23575
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/DanShaders ✅
7 changed files with 19 additions and 42 deletions
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15
Userland/Libraries/LibCrypto/BigInt/Algorithms/ModularPower.cpp
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@@ -16,7 +16,6 @@ void UnsignedBigIntegerAlgorithms::destructive_modular_power_without_allocation(
UnsignedBigInteger& temp_1,
UnsignedBigInteger& temp_2,
UnsignedBigInteger& temp_3,
UnsignedBigInteger& temp_4,
UnsignedBigInteger& temp_multiply,
UnsignedBigInteger& temp_quotient,
UnsignedBigInteger& temp_remainder,
@@ -27,17 +26,16 @@ void UnsignedBigIntegerAlgorithms::destructive_modular_power_without_allocation(
if (ep.words()[0] % 2 == 1) {
// exp = (exp * base) % m;
multiply_without_allocation(exp, base, temp_1, temp_2, temp_3, temp_multiply);
divide_without_allocation(temp_multiply, m, temp_1, temp_2, temp_3, temp_4, temp_quotient, temp_remainder);
divide_without_allocation(temp_multiply, m, temp_quotient, temp_remainder);
exp.set_to(temp_remainder);
}
// ep = ep / 2;
divide_u16_without_allocation(ep, 2, temp_quotient, temp_remainder);
ep.set_to(temp_quotient);
ep.set_to(ep.shift_right(1));
// base = (base * base) % m;
multiply_without_allocation(base, base, temp_1, temp_2, temp_3, temp_multiply);
divide_without_allocation(temp_multiply, m, temp_1, temp_2, temp_3, temp_4, temp_quotient, temp_remainder);
divide_without_allocation(temp_multiply, m, temp_quotient, temp_remainder);
base.set_to(temp_remainder);
// Note that not clamping here would cause future calculations (multiply, specifically) to allocate even more unused space
@@ -208,13 +206,13 @@ void UnsignedBigIntegerAlgorithms::montgomery_modular_power_with_minimal_allocat
// rr = ( 2 ^ (2 * modulo.length() * BITS_IN_WORD) ) % modulo
shift_left_by_n_words(one, 2 * num_words, x);
divide_without_allocation(x, modulo, temp_z, one, z, zz, temp_extra, rr);
divide_without_allocation(x, modulo, temp_extra, rr);
rr.resize_with_leading_zeros(num_words);
// x = base [% modulo, if x doesn't already fit in modulo's words]
x.set_to(base);
if (x.trimmed_length() > num_words)
divide_without_allocation(base, modulo, temp_z, one, z, zz, temp_extra, x);
divide_without_allocation(base, modulo, temp_extra, x);
x.resize_with_leading_zeros(num_words);
one.set_to(1);
@@ -274,11 +272,10 @@ void UnsignedBigIntegerAlgorithms::montgomery_modular_power_with_minimal_allocat
dbgln("Encountered the modulo branch during a montgomery modular power. Params : {} - {} - {}", base, exponent, modulo);
// We just clobber all the other temporaries that we don't need for the division.
// This is wasteful, but we're on the edgiest of cases already.
divide_without_allocation(zz, modulo, temp_z, rr, z, x, temp_extra, result);
divide_without_allocation(zz, modulo, temp_extra, result);
}
result.clamp_to_trimmed_length();
return;
}
}