This will allow replacing (currently buggy) mem.sliceAsBytes() usage in
the mem.Allocator implementation with, for example:
const bytes: []u8 = @constCast(@ptrCast(mem.absorbSentinel(allocation)));
References: https://github.com/ziglang/zig/pull/22706
I understand the temptation to exploit page size knowledge to make this function
faster, but I don't think this code can ever be compatible with any reasonable
set of pointer provenance/aliasing rules. At the very least, I don't believe it
is compatible with LLVM's.
closes https://github.com/ziglang/zig/issues/23184
Now that zig1.wasm is updated, apply the matching standard library
changes.
The main one is in `std.builtin.Type`, where `alignment` fields now have
type `?usize` rather than `comptime_int`.
Additionally, we need to add explicit backing integers to some packed
unions, because (due to https://github.com/ziglang/zig/issues/24714)
they need explicit backing integers to be used in `extern` contexts.
This change could not happen before now, because prior to this branch,
packed unions did not allow explicit backing integer types (that is,
this branch implemented https://github.com/ziglang/zig/issues/25350).
Commit dec1163fbb removed sentinels from the returned slice for C
pointers. Since C pointers have no bounds, we know that it'll keep
scanning until it finds `end` (or crash trying). The same is also true
of many-item pointers without a sentinel (e.g. `[*]T`), so I added
support for those too.
`findScalarPos` might do repetitive work, even if using simd. For
example, when searching the string `/abcde/fghijk/lm` for the character
`/`, a 16-byte wide search would yield `1000001000000100` but would only
count the first `1` and re-search the remaining of the string.
When testing locally, the difference was quite significative:
```
count scalar
5737 iterations 522.83us per iterations
0 bytes per iteration
worst: 2370us median: 512us stddev: 107.64us
count v2
38333 iterations 78.03us per iterations
0 bytes per iteration
worst: 713us median: 76us stddev: 10.62us
count scalar v2
99565 iterations 29.80us per iterations
0 bytes per iteration
worst: 41us median: 29us stddev: 1.04us
```
Note that `count v2` is a simpler string search, similar to the
remaining version of the simd approach:
```
pub fn countV2(comptime T: type, haystack: []const T, needle: T) usize {
const n = haystack.len;
if (n < 1) return 0;
var count: usize = 0;
for (haystack[0..n]) |item| {
count += @intFromBool(item == needle);
}
return count;
}
```
Which implies the compiler yields some optimized code for a simpler loop
that is more performant than the `findScalarPos`-based approach, hence
the usage of iterative approach for the remaining of the haystack.
Co-authored-by: StAlKeR7779 <stalkek7779@yandex.ru>
Moving towards our function naming convention of having one word per
concept and constructing function names out of concatenated concepts.
In `std.mem` the concepts are:
* "find" - return index of substring
* "pos" - starting index parameter
* "last" - search from the end
* "linear" - simple for loop rather than fancy algo
* "scalar" - substring is a single element
* Document std.mem.* functions
Functions in std.mem are essential for virtually all applications,
yet many of them lacked documentation.
Co-authored-by: Andrew Kelley <andrew@ziglang.org>
Basically everything that has a direct replacement or no uses left.
Notable omissions:
- std.ArrayHashMap: Too much fallout, needs a separate cleanup.
- std.debug.runtime_safety: Too much fallout.
- std.heap.GeneralPurposeAllocator: Lots of references to it remain, not
a simple find and replace as "debug allocator" is not equivalent to
"general purpose allocator".
- std.io.Reader: Is being reworked at the moment.
- std.unicode.utf8Decode(): No replacement, needs a new API first.
- Manifest backwards compat options: Removal would break test data used
by TestFetchBuilder.
- panic handler needs to be a namespace: Many tests still rely on it
being a function, needs a separate cleanup.
Nothing interesting here; literally just the bare minimum so I can work on this
on and off in a branch without worrying about merge conflicts in the non-backend
code.
Alex Rønne Petersen