55 lines
2.0 KiB
Rust
55 lines
2.0 KiB
Rust
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use rand_xoshiro::rand_core::{RngCore, SeedableRng};
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use rand_xoshiro::Xoshiro128StarStar;
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use compiler_builtins::int::__clzsi2;
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use compiler_builtins::int::leading_zeros::{
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usize_leading_zeros_default, usize_leading_zeros_riscv,
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};
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#[test]
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fn __clzsi2_test() {
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// Binary fuzzer. We cannot just send a random number directly to `__clzsi2()`, because we need
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// large sequences of zeros to test. This XORs, ANDs, and ORs random length strings of 1s to
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// `x`. ORs insure sequences of ones, ANDs insures sequences of zeros, and XORs are not often
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// destructive but add entropy.
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let mut rng = Xoshiro128StarStar::seed_from_u64(0);
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let mut x = 0usize;
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// creates a mask for indexing the bits of the type
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let bit_indexing_mask = usize::MAX.count_ones() - 1;
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// 10000 iterations is enough to make sure edge cases like single set bits are tested and to go
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// through many paths.
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for _ in 0..10_000 {
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let r0 = bit_indexing_mask & rng.next_u32();
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// random length of ones
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let ones: usize = !0 >> r0;
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let r1 = bit_indexing_mask & rng.next_u32();
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// random circular shift
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let mask = ones.rotate_left(r1);
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match rng.next_u32() % 4 {
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0 => x |= mask,
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1 => x &= mask,
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// both 2 and 3 to make XORs as common as ORs and ANDs combined
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_ => x ^= mask,
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}
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let lz = x.leading_zeros() as usize;
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let lz0 = __clzsi2(x);
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let lz1 = usize_leading_zeros_default(x);
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let lz2 = usize_leading_zeros_riscv(x);
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if lz0 != lz {
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panic!("__clzsi2({}): expected: {}, found: {}", x, lz, lz0);
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}
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if lz1 != lz {
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panic!(
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"usize_leading_zeros_default({}): expected: {}, found: {}",
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x, lz, lz1
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);
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}
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if lz2 != lz {
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panic!(
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"usize_leading_zeros_riscv({}): expected: {}, found: {}",
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x, lz, lz2
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);
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}
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}
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}
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