num: Implement uint_gather_scatter_bits feature for unsigned integers
#149097
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Implement `gather_bits`, `scatter_bits` functions on unsigned integers Add tests to coretests
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rustbot has assigned @Mark-Simulacrum. Use |
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okaneco
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Nov 19, 2025
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| fn test_gather_bits() { | ||
| assert_eq_const_safe!($T: A.gather_bits(B), 0b_0010); | ||
| assert_eq_const_safe!($T: A.gather_bits(C), 0b_1010); | ||
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| assert_eq_const_safe!($T: B.gather_bits(A), 0b_0100); | ||
| assert_eq_const_safe!($T: B.gather_bits(C), 0b_1001); | ||
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| assert_eq_const_safe!($T: C.gather_bits(A), 0b_0110); | ||
| assert_eq_const_safe!($T: C.gather_bits(B), 0b_0011); | ||
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| assert_eq_const_safe!($T: A.gather_bits(_0), 0); | ||
| assert_eq_const_safe!($T: B.gather_bits(_0), 0); | ||
| assert_eq_const_safe!($T: C.gather_bits(_0), 0); | ||
| assert_eq_const_safe!($T: _0.gather_bits(A), 0); | ||
| assert_eq_const_safe!($T: _0.gather_bits(B), 0); | ||
| assert_eq_const_safe!($T: _0.gather_bits(C), 0); | ||
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| assert_eq_const_safe!($T: A.gather_bits(_1), A); | ||
| assert_eq_const_safe!($T: B.gather_bits(_1), B); | ||
| assert_eq_const_safe!($T: C.gather_bits(_1), C); | ||
| assert_eq_const_safe!($T: _1.gather_bits(A), 0b0000_0111); | ||
| assert_eq_const_safe!($T: _1.gather_bits(B), 0b0000_0011); | ||
| assert_eq_const_safe!($T: _1.gather_bits(C), 0b0001_1111); | ||
| } | ||
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| fn test_scatter_bits() { | ||
| assert_eq_const_safe!($T: A.scatter_bits(B), 0); | ||
| assert_eq_const_safe!($T: A.scatter_bits(C), 0b0011_0000); | ||
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| assert_eq_const_safe!($T: B.scatter_bits(A), 0b0000_0100); | ||
| assert_eq_const_safe!($T: B.scatter_bits(C), 0b0000_0001); | ||
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| assert_eq_const_safe!($T: C.scatter_bits(A), 0b_0000_0100); | ||
| assert_eq_const_safe!($T: C.scatter_bits(B), 0b_0000_0001); | ||
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| assert_eq_const_safe!($T: A.scatter_bits(_0), 0); | ||
| assert_eq_const_safe!($T: B.scatter_bits(_0), 0); | ||
| assert_eq_const_safe!($T: C.scatter_bits(_0), 0); | ||
| assert_eq_const_safe!($T: _0.scatter_bits(A), 0); | ||
| assert_eq_const_safe!($T: _0.scatter_bits(B), 0); | ||
| assert_eq_const_safe!($T: _0.scatter_bits(C), 0); | ||
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| assert_eq_const_safe!($T: A.scatter_bits(_1), A); | ||
| assert_eq_const_safe!($T: B.scatter_bits(_1), B); | ||
| assert_eq_const_safe!($T: C.scatter_bits(_1), C); | ||
| assert_eq_const_safe!($T: _1.scatter_bits(A), A); | ||
| assert_eq_const_safe!($T: _1.scatter_bits(B), B); | ||
| assert_eq_const_safe!($T: _1.scatter_bits(C), C); | ||
| } |
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These tests are difficult to manually review without seeing the constants, so I've duplicated the values and used the x86 intrinsics to show the tests produce the same values.
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Feature gate:
#![feature(uint_gather_scatter_bits)]Tracking issue: #149069
Accepted ACP: rust-lang/libs-team#695 (comment)
Implement
gather_bits,scatter_bitsfunctions on unsigned integersAdd tests to coretests
This implementation is a small improvement over the plain naive form (see the solution sketch).
We only check the set bits in the mask instead of iterating over every bit.