Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

libcore: fix compilation on 16bit target (MSP430). #40832

Merged
merged 2 commits into from
Mar 30, 2017
Merged
Changes from all commits
Commits
File filter

Filter by extension

Filter by extension

Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
58 changes: 34 additions & 24 deletions src/libcore/slice/sort.rs
Original file line number Diff line number Diff line change
Expand Up @@ -498,32 +498,42 @@ fn partition_equal<T, F>(v: &mut [T], pivot: usize, is_less: &mut F) -> usize
#[cold]
fn break_patterns<T>(v: &mut [T]) {
let len = v.len();

if len >= 8 {
// A random number will be taken modulo this one. The modulus is a power of two so that we
// can simply take bitwise "and", thus avoiding costly CPU operations.
let modulus = (len / 4).next_power_of_two();
debug_assert!(modulus >= 1 && modulus <= len / 2);

// Pseudorandom number generation from the "Xorshift RNGs" paper by George Marsaglia.
let mut random = len;
random ^= random << 13;
random ^= random >> 17;
random ^= random << 5;
random &= modulus - 1;
debug_assert!(random < len / 2);

// The first index.
let a = len / 4 * 2;
debug_assert!(a >= 1 && a < len - 2);

// The second index.
let b = len / 4 + random;
debug_assert!(b >= 1 && b < len - 2);

// Swap neighbourhoods of `a` and `b`.
// Pseudorandom number generator from the "Xorshift RNGs" paper by George Marsaglia.
let mut random = len as u32;
let mut gen_u32 = || {
random ^= random << 13;
random ^= random >> 17;
random ^= random << 5;
random
};
let mut gen_usize = || {
if mem::size_of::<usize>() <= 4 {
gen_u32() as usize
} else {
(((gen_u32() as u64) << 32) | (gen_u32() as u64)) as usize
}
};

// Take random numbers modulo this number.
// The number fits into `usize` because `len` is not greater than `isize::MAX`.
let modulus = len.next_power_of_two();

// Some pivot candidates will be in the nearby of this index. Let's randomize them.
let pos = len / 4 * 2;

for i in 0..3 {
v.swap(a - 1 + i, b - 1 + i);
// Generate a random number modulo `len`. However, in order to avoid costly operations
// we first take it modulo a power of two, and then decrease by `len` until it fits
// into the range `[0, len - 1]`.
let mut other = gen_usize() & (modulus - 1);

// `other` is guaranteed to be less than `2 * len`.
if other >= len {
other -= len;
}

v.swap(pos - 1 + i, other);
}
}
}
Expand Down