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Properly support passing a packed struct to byteSwapAllFields #25698

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Properly support passing a packed struct to byteSwapAllFields #25698

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2530afb
Properly support passing a packed struct to byteSwapAllFields
SquareMan Oct 25, 2025
fecbe38
Support inner structs with alignment in byteSwapAllFields
SquareMan Oct 29, 2025
80a051e
Merge branch 'master' into byteSwapAllFields
SquareMan Nov 3, 2025
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48 changes: 40 additions & 8 deletions lib/std/mem.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -2284,16 +2284,20 @@ test writeVarPackedInt {
/// Swap the byte order of all the members of the fields of a struct
/// (Changing their endianness)
pub fn byteSwapAllFields(comptime S: type, ptr: *S) void {
byteSwapAllFieldsAligned(S, @alignOf(S), ptr);
}

/// Swap the byte order of all the members of the fields of a struct
/// (Changing their endianness)
pub fn byteSwapAllFieldsAligned(comptime S: type, comptime A: comptime_int, ptr: *align(A) S) void {
switch (@typeInfo(S)) {
.@"struct" => {
inline for (std.meta.fields(S)) |f| {
.@"struct" => |struct_info| {
if (struct_info.backing_integer) |Int| {
ptr.* = @bitCast(@byteSwap(@as(Int, @bitCast(ptr.*))));
} else inline for (std.meta.fields(S)) |f| {
switch (@typeInfo(f.type)) {
.@"struct" => |struct_info| if (struct_info.backing_integer) |Int| {
@field(ptr, f.name) = @bitCast(@byteSwap(@as(Int, @bitCast(@field(ptr, f.name)))));
} else {
byteSwapAllFields(f.type, &@field(ptr, f.name));
},
.@"union", .array => byteSwapAllFields(f.type, &@field(ptr, f.name)),
.@"struct" => byteSwapAllFieldsAligned(f.type, f.alignment, &@field(ptr, f.name)),
.@"union", .array => byteSwapAllFieldsAligned(f.type, f.alignment, &@field(ptr, f.name)),
.@"enum" => {
@field(ptr, f.name) = @enumFromInt(@byteSwap(@intFromEnum(@field(ptr, f.name))));
},
Expand Down Expand Up @@ -2349,6 +2353,20 @@ test byteSwapAllFields {
f4: bool,
f5: f32,
};
const P = packed struct(u32) {
f0: u1,
f1: u7,
f2: u4,
f3: u4,
f4: u16,
};
const A = extern struct {
f0: u32,
f1: extern struct {
f0: u64,
} align(4),
f2: u32,
};
var s = T{
.f0 = 0x12,
.f1 = 0x1234,
Expand All @@ -2366,8 +2384,16 @@ test byteSwapAllFields {
.f4 = false,
.f5 = @as(f32, @bitCast(@as(u32, 0x45d42800))),
};
var p: P = @bitCast(@as(u32, 0x01234567));
var a: A = A{
.f0 = 0x12345678,
.f1 = .{ .f0 = 0x123456789ABCDEF0 },
.f2 = 0x87654321,
};
byteSwapAllFields(T, &s);
byteSwapAllFields(K, &k);
byteSwapAllFields(P, &p);
byteSwapAllFields(A, &a);
try std.testing.expectEqual(T{
.f0 = 0x12,
.f1 = 0x3412,
Expand All @@ -2385,6 +2411,12 @@ test byteSwapAllFields {
.f4 = false,
.f5 = @as(f32, @bitCast(@as(u32, 0x0028d445))),
}, k);
try std.testing.expectEqual(@as(P, @bitCast(@as(u32, 0x67452301))), p);
try std.testing.expectEqual(A{
.f0 = 0x78563412,
.f1 = .{ .f0 = 0xF0DEBC9A78563412 },
.f2 = 0x21436587,
}, a);
}

/// Reverses the byte order of all elements in a slice.
Expand Down