From fa3228ae42d3bc92ad66fe91e108511583129ffd Mon Sep 17 00:00:00 2001
From: Ivel <ivel.santos@proton.me>
Date: Thu, 5 Feb 2026 20:21:41 +0100
Subject: [PATCH] libc: reimplement swab in Zig (#31130)

This PR replaces the bundled musl swab() implementation with zig's one.

Contributes towards #30978.

It looks like there are not test cases for swab() in test-libc.

Reviewed-on: https://codeberg.org/ziglang/zig/pulls/31130
Reviewed-by: Andrew Kelley <andrew@ziglang.org>
Co-authored-by: Ivel <ivel.santos@proton.me>
Co-committed-by: Ivel <ivel.santos@proton.me>
---
 lib/c/unistd.zig                | 42 +++++++++++++++++++++++++++++++++
 lib/libc/musl/src/string/swab.c | 13 ----------
 src/libs/musl.zig               |  1 -
 src/libs/wasi_libc.zig          |  1 -
 4 files changed, 42 insertions(+), 15 deletions(-)
 delete mode 100644 lib/libc/musl/src/string/swab.c

diff --git a/lib/c/unistd.zig b/lib/c/unistd.zig
index f903ef78a8..98290f0e04 100644
--- a/lib/c/unistd.zig
+++ b/lib/c/unistd.zig
@@ -43,6 +43,9 @@ comptime {
 
         @export(&execveLinux, .{ .name = "execve", .linkage = common.linkage, .visibility = common.visibility });
     }
+    if (builtin.target.isMuslLibC() or builtin.target.isWasiLibC()) {
+        @export(&swab, .{ .name = "swab", .linkage = common.linkage, .visibility = common.visibility });
+    }
 }
 
 fn _exit(exit_code: c_int) callconv(.c) noreturn {
@@ -181,3 +184,42 @@ fn unlinkatLinux(fd: c_int, path: [*:0]const c_char, flags: c_int) callconv(.c)
 fn execveLinux(path: [*:0]const c_char, argv: [*:null]const ?[*:0]c_char, envp: [*:null]const ?[*:0]c_char) callconv(.c) c_int {
     return common.errno(linux.execve(@ptrCast(path), @ptrCast(argv), @ptrCast(envp)));
 }
+
+fn swab(noalias src_ptr: *const anyopaque, noalias dest_ptr: *anyopaque, n: isize) callconv(.c) void {
+    var src: [*]const u8 = @ptrCast(src_ptr);
+    var dest: [*]u8 = @ptrCast(dest_ptr);
+    var i = n;
+
+    while (i > 1) : (i -= 2) {
+        dest[0] = src[1];
+        dest[1] = src[0];
+        dest += 2;
+        src += 2;
+    }
+}
+
+test swab {
+    var a: [4]u8 = undefined;
+    @memset(a[0..], '\x00');
+    swab("abcd", &a, 4);
+    try std.testing.expectEqualSlices(u8, "badc", &a);
+
+    // Partial copy
+    @memset(a[0..], '\x00');
+    swab("abcd", &a, 2);
+    try std.testing.expectEqualSlices(u8, "ba\x00\x00", &a);
+
+    // n < 1
+    @memset(a[0..], '\x00');
+    swab("abcd", &a, 0);
+    try std.testing.expectEqualSlices(u8, "\x00" ** 4, &a);
+    swab("abcd", &a, -1);
+    try std.testing.expectEqualSlices(u8, "\x00" ** 4, &a);
+
+    // Odd n
+    @memset(a[0..], '\x00');
+    swab("abcd", &a, 1);
+    try std.testing.expectEqualSlices(u8, "\x00" ** 4, &a);
+    swab("abcd", &a, 3);
+    try std.testing.expectEqualSlices(u8, "ba\x00\x00", &a);
+}
diff --git a/lib/libc/musl/src/string/swab.c b/lib/libc/musl/src/string/swab.c
deleted file mode 100644
index ace0f4666d..0000000000
--- a/lib/libc/musl/src/string/swab.c
+++ /dev/null
@@ -1,13 +0,0 @@
-#include <unistd.h>
-
-void swab(const void *restrict _src, void *restrict _dest, ssize_t n)
-{
-	const char *src = _src;
-	char *dest = _dest;
-	for (; n>1; n-=2) {
-		dest[0] = src[1];
-		dest[1] = src[0];
-		dest += 2;
-		src += 2;
-	}
-}
diff --git a/src/libs/musl.zig b/src/libs/musl.zig
index 1974e0e4ea..ebbd285665 100644
--- a/src/libs/musl.zig
+++ b/src/libs/musl.zig
@@ -1579,7 +1579,6 @@ const src_files = [_][]const u8{
     "musl/src/string/strndup.c",
     "musl/src/string/strsignal.c",
     "musl/src/string/strverscmp.c",
-    "musl/src/string/swab.c",
     "musl/src/string/wcscasecmp.c",
     "musl/src/string/wcscasecmp_l.c",
     "musl/src/string/wcsdup.c",
diff --git a/src/libs/wasi_libc.zig b/src/libs/wasi_libc.zig
index 8e0ade2a0d..24a0ead598 100644
--- a/src/libs/wasi_libc.zig
+++ b/src/libs/wasi_libc.zig
@@ -957,7 +957,6 @@ const libc_top_half_src_files = [_][]const u8{
     "musl/src/string/strerror_r.c",
     "musl/src/string/strndup.c",
     "musl/src/string/strverscmp.c",
-    "musl/src/string/swab.c",
     "musl/src/string/wcscasecmp.c",
     "musl/src/string/wcscasecmp_l.c",
     "musl/src/string/wcsdup.c",