Support i64.mul_wide_s and i64.mul_wide_u from Wide Arithmetic proposal#8652
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stevenfontanella wants to merge 1 commit intomainfrom
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Support i64.mul_wide_s and i64.mul_wide_u from Wide Arithmetic proposal#8652stevenfontanella wants to merge 1 commit intomainfrom
stevenfontanella wants to merge 1 commit intomainfrom
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MaxGraey
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Apr 28, 2026
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tlively
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| // Copyright 2024 WebAssembly Community Group participants | |||
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| // Copyright 2024 WebAssembly Community Group participants | |
| // Copyright 2026 WebAssembly Community Group participants |
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| // Copyright 2024 WebAssembly Community Group participants | |||
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| // Copyright 2024 WebAssembly Community Group participants | |
| // Copyright 2026 WebAssembly Community Group participants |
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| uint64_t cross = mulLowHigh + (mulLowLow >> 32); | ||
| uint64_t carry = cross >> 32; | ||
| cross = (cross & 0xffffffff) + mulHighLow; |
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It's not immediately obvious to me how cross corresponds to the explanatory comments below. It would be good to make sure the code directly follows from the comments.
It might also be helpful to start with a comment like result = (lhsHigh * 2^32 + lhsLow) * (rhsHigh * 2^32 + rhsLow) = lhsHigh * rhsHigh * 2^64 + lhsHigh * rhsLow * 2^32 + lhsLow * rhsHigh * 2^32 + lhsLow * rhsLow
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| namespace detail { | ||
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| Int128 mul_wide_s_fallback(uint64_t lhs, uint64_t rhs) { |
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It would be nice to have some comments explaining the math here, too.
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| // Copyright 2024 WebAssembly Community Group participants | |||
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| // Copyright 2026 WebAssembly Community Group participants |
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| INSTANTIATE_TEST_SUITE_P(Int128, | ||
| Int128MulWideSTest, | ||
| ::testing::Values(mul_wide_s, | ||
| detail::mul_wide_s_fallback)); |
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What does this do? I've never seen TEST_P before.
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| int64_t maxInt = std::numeric_limits<int64_t>::max(); | ||
| // Fits in the lower half because the signed bit now goes in the upper half. | ||
| EXPECT_EQ(mul_s(maxInt, 2), (Int128{0, 0xfffffffffffffffeULL})); |
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It would be nice to show that reversing the order of operands doesn't change the results here and below.
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Part of #8544. Unit tests were written by Gemini and double-checked against python with this script.
TODO: Move the existing 128 add/sub logic from the interpreter into int128.h.