The old definitions had some problems:
- In `lowerBound`, the `lhs` (left hand side) argument was passed on the
right hand side.
- In `upperBound`, the `greaterThan` function needed to return
`greaterThanOrEqual` for the function work, so either the name or the
implementation is incorrect.
To fix both problems, define the functions in terms of a `lessThan` function that returns `lhs < rhs`.
The is more consistent with the rest of `sort.zig` and it's also how C++ implements lower/upperBound (1)(2).
(1) https://en.cppreference.com/w/cpp/algorithm/lower_bound
(2) https://en.cppreference.com/w/cpp/algorithm/upper_bound
- Rewrite doc comments.
- Add a couple of more test cases.
- Add docstring for std.sort.binarySearch
Authored by https://github.com/CraigglesO
Original Discussion: #9890
I already had to create these functions and test cases for my own
project so I decided to contribute to the main code base in hopes it
would simplify my own.
I realize this is still under discussion but this was a trivial amount
of work so I thought I could help nudge the discussion towards a
decision.
Why add these to the standard library
To better illustrate and solidify their value, the standard library's
"sort" module already contains several binary search queries on arrays
such as binarySearch and internal functions binaryFirst & binaryLast. A
final example of its use: the Zig code itself created and used a
bounding search in the linker.
There still lacks the ability to allow the programmer themselves to
search the array for a rough position and find an index to read &/
update.
Adding these functions would also help to complement dynamic structures
like ArrayList with it's insert function.
Example Case
I'm building a library in Zig for GIS geometry. To store points, lines,
and polygons each 3D point is first translated into what's called an
S2CellId. This is a fancy way of saying I reduce the Earth's spherical
data into a 1D Hilbert Curve with cm precision. This gives me 2
convenient truths:
Hilbert Curves have locality of reference.
All points can be stored inside a 1D array
Since lowerBound and upperBound to find data inside a radius for
instance. If I'm interested in a specific cell at a specific "level" and
want to iterate all duplicates, equalRange is a best fit.
As pointed out in the issue this behavior test branches on an undefined
value. That's not valid Zig code.
Also behavior tests should not depend on the standard library in this
manner. They need to minimally isolate the specific language thing that
is being tested.
Closes#12681
