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std.io.AllocatingWriter.writeSplat: better implementation

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This commit is contained in:
Andrew Kelley 2025-04-21 22:01:37 -07:00
parent d9b9e3c272
commit 045c1c1557
1 changed files with 9 additions and 11 deletions
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20
lib/std/io/AllocatingWriter.zig
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@ -130,6 +130,7 @@ pub fn clearRetainingCapacity(aw: *AllocatingWriter) void {
}
fn writeSplat(context: ?*anyopaque, data: []const []const u8, splat: usize) std.io.Writer.Error!usize {
if (data.len == 0 and splat == 0) return 0;
const aw: *AllocatingWriter = @alignCast(@ptrCast(context));
const start_len = aw.written.len;
const bw = &aw.buffered_writer;
@ -140,26 +141,23 @@ fn writeSplat(context: ?*anyopaque, data: []const []const u8, splat: usize) std.
.capacity = start_len + bw.buffer.len,
};
defer setArrayList(aw, list);
const rest = data[1 .. data.len - 1];
const rest = if (splat == 0) data[1 .. data.len - 1] else data[1..];
const pattern = data[data.len - 1];
var new_capacity: usize = list.capacity + pattern.len * splat;
const remaining_splat = splat - 1;
var new_capacity: usize = list.capacity + pattern.len * remaining_splat;
for (rest) |bytes| new_capacity += bytes.len;
list.ensureTotalCapacity(aw.allocator, new_capacity + 1) catch return error.WriteFailed;
for (rest) |bytes| list.appendSliceAssumeCapacity(bytes);
appendPatternAssumeCapacity(&list, pattern, splat);
if (pattern.len == 1) {
list.appendNTimesAssumeCapacity(pattern[0], remaining_splat);
} else {
for (0..remaining_splat) |_| list.appendSliceAssumeCapacity(pattern);
}
aw.written = list.items;
bw.buffer = list.unusedCapacitySlice();
return list.items.len - start_len;
}
fn appendPatternAssumeCapacity(list: *std.ArrayListUnmanaged(u8), pattern: []const u8, splat: usize) void {
if (pattern.len == 1) {
list.appendNTimesAssumeCapacity(pattern[0], splat);
} else {
for (0..splat) |_| list.appendSliceAssumeCapacity(pattern);
}
}
fn writeFile(
context: ?*anyopaque,
file: std.fs.File,