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multiprecision: ignore buggy -Waggressive-loop-optimizations in subtraction #334

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Feb 17, 2025
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multiprecision: ignore buggy -Waggressive-loop-optimizations in subtraction #334

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28 changes: 25 additions & 3 deletions ...to3/libs/multiprecision/include/nil/crypto3/multiprecision/detail/big_uint/arithmetic.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -78,14 +78,16 @@ namespace nil::crypto3::multiprecision {
#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic push
// Disable a false positive triggered by
// -Waggressive-loop-optimizations
// -Waggressive-loop-optimizations.
//
// The warning message is "warning:
// iteration 2305843009213693951 invokes undefined behavior
// [-Waggressive-loop-optimizations]"
// [-Waggressive-loop-optimizations]".
//
// Of course if i becomes 2^61
// uint64_t will overflow, this is expected
// uint64_t will overflow, this is expected.
//
// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100801
#pragma GCC diagnostic ignored "-Waggressive-loop-optimizations"
#endif

Expand Down Expand Up @@ -285,7 +287,27 @@ namespace nil::crypto3::multiprecision {
borrow = subborrow(borrow, pa[i + 3], pb[i + 3], pr + i + 3);
}
for (; i < m; ++i) {
#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic push
// Disable a false positive triggered by
// -Waggressive-loop-optimizations.
//
// The warning message is "warning:
// iteration 2305843009213693951 invokes undefined behavior
// [-Waggressive-loop-optimizations]".
//
// Of course if i becomes 2^61
// uint64_t will overflow, this is expected.
//
// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100801
#pragma GCC diagnostic ignored "-Waggressive-loop-optimizations"
#endif

borrow = subborrow(borrow, pa[i], pb[i], pr + i);

#if defined(__GNUC__) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
}
// Now where only a has digits, only as long as we've borrowed:
while (borrow && (i < as)) {
Expand Down