compiler-builtins-zynq/testcrate/tests/leading_zeros.rs

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2020-07-29 02:09:18 +08:00
use rand_xoshiro::rand_core::{RngCore, SeedableRng};
use rand_xoshiro::Xoshiro128StarStar;
use compiler_builtins::int::__clzsi2;
use compiler_builtins::int::leading_zeros::{
usize_leading_zeros_default, usize_leading_zeros_riscv,
};
#[test]
fn __clzsi2_test() {
// Binary fuzzer. We cannot just send a random number directly to `__clzsi2()`, because we need
// large sequences of zeros to test. This XORs, ANDs, and ORs random length strings of 1s to
// `x`. ORs insure sequences of ones, ANDs insures sequences of zeros, and XORs are not often
// destructive but add entropy.
let mut rng = Xoshiro128StarStar::seed_from_u64(0);
let mut x = 0usize;
// creates a mask for indexing the bits of the type
let bit_indexing_mask = usize::MAX.count_ones() - 1;
// 10000 iterations is enough to make sure edge cases like single set bits are tested and to go
// through many paths.
for _ in 0..10_000 {
let r0 = bit_indexing_mask & rng.next_u32();
// random length of ones
let ones: usize = !0 >> r0;
let r1 = bit_indexing_mask & rng.next_u32();
// random circular shift
let mask = ones.rotate_left(r1);
match rng.next_u32() % 4 {
0 => x |= mask,
1 => x &= mask,
// both 2 and 3 to make XORs as common as ORs and ANDs combined
_ => x ^= mask,
}
let lz = x.leading_zeros() as usize;
let lz0 = __clzsi2(x);
let lz1 = usize_leading_zeros_default(x);
let lz2 = usize_leading_zeros_riscv(x);
if lz0 != lz {
panic!("__clzsi2({}): expected: {}, found: {}", x, lz, lz0);
}
if lz1 != lz {
panic!(
"usize_leading_zeros_default({}): expected: {}, found: {}",
x, lz, lz1
);
}
if lz2 != lz {
panic!(
"usize_leading_zeros_riscv({}): expected: {}, found: {}",
x, lz, lz2
);
}
}
}