options/posix: Implement swab

options/posix/generic/unistd-stubs.cpp

@@ -666,9 +666,15 @@ int setuid(uid_t uid) {
 	return 0;
 }
 
-void swab(const void *__restrict, void *__restrict, ssize_t) {
-	__ensure(!"Not implemented");
-	__builtin_unreachable();
+void swab(const void *_src, void *_dest, ssize_t n) {
+	const char *src = reinterpret_cast<const char *>(_src);
+	char *dest = reinterpret_cast<char *>(_dest);
+	for(; n > 1; n -= 2) {
+		dest[0] = src[1];
+		dest[1] = src[0];
+		dest += 2;
+		src += 2;
+	}
 }
 
 int symlink(const char *target_path, const char *link_path) {

tests/meson.build

@@ -98,6 +98,7 @@ all_test_cases = [
 	'posix/mkstemp',
 	'posix/waitid',
 	'posix/usershell',
+	'posix/swab',
 	'glibc/getopt',
 	'glibc/ffsl-ffsll',
 	'glibc/error_message_count',

tests/posix/swab.c

@@ -0,0 +1,66 @@
+#include <assert.h>
+#include <stdint.h>
+#include <unistd.h>
+
+void test_swab_even_bytes() {
+	uint8_t input[] = {0x01, 0x02, 0x03, 0x04};
+	uint8_t output[4];
+
+	swab(input, output, sizeof(input));
+
+	assert(output[0] == 0x02);
+	assert(output[1] == 0x01);
+	assert(output[2] == 0x04);
+	assert(output[3] == 0x03);
+}
+
+void test_swab_odd_bytes() {
+	uint8_t input[] = {0x01, 0x02, 0x03, 0x04, 0x05};
+	uint8_t output[5];
+
+	swab(input, output, sizeof(input));
+
+	assert(output[0] == 0x02);
+	assert(output[1] == 0x01);
+	assert(output[2] == 0x04);
+	assert(output[3] == 0x03);
+
+	// Last byte is UB, assume unchanged?
+	assert(output[4] == 0x05);
+}
+
+void test_swab_negative_bytes() {
+	uint8_t input[] = {0x01, 0x02, 0x03, 0x04};
+	uint8_t output[4];
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstringop-overflow"
+	swab(input, output, -1); // Should change nothing
+#pragma GCC diagnostic pop
+
+	assert(output[0] == 0x01);
+	assert(output[1] == 0x02);
+	assert(output[2] == 0x03);
+	assert(output[3] == 0x04);
+}
+
+void test_swab_zero_bytes() {
+	uint8_t input[] = {0x01, 0x02, 0x03, 0x04};
+	uint8_t output[4];
+
+	swab(input, output, 0); // Should change nothing
+
+	assert(output[0] == 0x01);
+	assert(output[1] == 0x02);
+	assert(output[2] == 0x03);
+	assert(output[3] == 0x04);
+}
+
+int main() {
+	test_swab_even_bytes();
+	test_swab_odd_bytes();
+	test_swab_negative_bytes();
+	test_swab_zero_bytes();
+
+	return 0;
+}