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This commit is contained in:
Paul Masurel
2021-10-18 12:52:43 +09:00
committed by GitHub
parent b5b1244857
commit d18ac136c0
1 changed files with 9 additions and 20 deletions
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29
src/postings/block_search.rs
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@@ -1,14 +1,5 @@
use crate::postings::compression::COMPRESSION_BLOCK_SIZE;
unsafe fn binary_search_step(ptr: *const u32, target: u32, half_size: isize) -> *const u32 {
let mid = ptr.offset(half_size);
if *mid < target {
mid.offset(1)
} else {
ptr
}
}
/// Search the first index containing an element greater or equal to
/// the target.
///
@@ -30,18 +21,16 @@ unsafe fn binary_search_step(ptr: *const u32, target: u32, half_size: isize) ->
/// end of the last block for instance.
/// - The target is assumed smaller or equal to the last element of the block.
pub fn branchless_binary_search(arr: &[u32; COMPRESSION_BLOCK_SIZE], target: u32) -> usize {
let start_ptr: *const u32 = &arr[0] as *const u32;
unsafe {
let mut ptr = start_ptr;
ptr = binary_search_step(ptr, target, 63);
ptr = binary_search_step(ptr, target, 31);
ptr = binary_search_step(ptr, target, 15);
ptr = binary_search_step(ptr, target, 7);
ptr = binary_search_step(ptr, target, 3);
ptr = binary_search_step(ptr, target, 1);
let extra = if *ptr < target { 1 } else { 0 };
(ptr.offset_from(start_ptr) as usize) + extra
let mut start = 0;
let mut len = arr.len();
for _ in 0..7 {
len /= 2;
let pivot = unsafe { *arr.get_unchecked(start + len - 1) };
if pivot < target {
start += len;
}
}
start
}
#[cfg(test)]