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std.fs.File: use file size as ArrayList initial capacity

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This commit is contained in:
Nuno Mendes 2024-09-29 17:57:29 +02:00
parent 3b465ebec5
commit c6ac45bced
1 changed files with 16 additions and 6 deletions
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22
lib/std/fs/File.zig
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@ -1149,13 +1149,23 @@ pub fn readToEndAllocOptions(
comptime alignment: u29,
comptime optional_sentinel: ?u8,
) !(if (optional_sentinel) |s| [:s]align(alignment) u8 else []align(alignment) u8) {
// If no size hint is provided fall back to the size=0 code path
const size = size_hint orelse 0;
var size: usize = undefined;
if (size_hint) |hint| {
size = hint;
} else {
// If no size hint is provided the file size returned by stat() is used as a
// hint to set the buffer size.
const file_stat = self.stat();
if (file_stat) |value| {
size = std.math.cast(usize, value.size) orelse return error.FileTooBig;
} else |_| {
// If the reported size is zero or there was an error reading stat(),
// for example on Linux for files in /proc, a small buffer is allocated instead.
size = 1024;
}
}
// The file size returned by stat is used as hint to set the buffer
// size. If the reported size is zero, as it happens on Linux for files
// in /proc, a small buffer is allocated instead.
const initial_cap = (if (size > 0) size else 1024) + @intFromBool(optional_sentinel != null);
const initial_cap = size + @intFromBool(optional_sentinel != null);
var array_list = try std.ArrayListAligned(u8, alignment).initCapacity(allocator, initial_cap);
defer array_list.deinit();