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std.io.Writer.writeSplat: simplify and fix

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This commit is contained in:
Andrew Kelley 2025-07-09 17:52:36 -07:00
parent ab84dcc824
commit 09cdcf67e1
1 changed files with 13 additions and 14 deletions
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27
lib/std/io/Writer.zig
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@ -162,28 +162,20 @@ pub fn writeSplat(w: *Writer, data: []const []const u8, splat: usize) Error!usiz
const buffer = w.buffer;
const count = countSplat(data, splat);
if (w.end + count > buffer.len) return w.vtable.drain(w, data, splat);
for (data) |bytes| {
for (data[0 .. data.len - 1]) |bytes| {
@memcpy(buffer[w.end..][0..bytes.len], bytes);
w.end += bytes.len;
}
const pattern = data[data.len - 1];
if (splat == 0) {
@branchHint(.unlikely);
w.end -= pattern.len;
return count;
}
const remaining_splat = splat - 1;
switch (pattern.len) {
0 => {},
1 => {
@memset(buffer[w.end..][0..remaining_splat], pattern[0]);
w.end += remaining_splat;
@memset(buffer[w.end..][0..splat], pattern[0]);
w.end += splat;
},
else => {
const new_end = w.end + pattern.len * remaining_splat;
while (w.end < new_end) : (w.end += pattern.len) {
@memcpy(buffer[w.end..][0..pattern.len], pattern);
}
else => for (0..splat) |_| {
@memcpy(buffer[w.end..][0..pattern.len], pattern);
w.end += pattern.len;
},
}
return count;
@ -2118,6 +2110,13 @@ test "fixed output" {
try testing.expect(std.mem.eql(u8, w.buffered(), "Hello worl"));
}
test "writeSplat 0 len splat larger than capacity" {
var buf: [8]u8 = undefined;
var w: std.io.Writer = .fixed(&buf);
const n = try w.writeSplat(&.{"something that overflows buf"}, 0);
try testing.expectEqual(0, n);
}
pub fn failingDrain(w: *Writer, data: []const []const u8, splat: usize) Error!usize {
_ = w;
_ = data;