Implement swab

src/header/unistd/mod.rs

@@ -555,9 +555,20 @@ pub extern "C" fn sleep(seconds: c_uint) -> c_uint {
     0
 }
 
-// #[no_mangle]
+#[no_mangle]
 pub extern "C" fn swab(src: *const c_void, dest: *mut c_void, nbytes: ssize_t) {
-    unimplemented!();
+    if nbytes <= 0 {
+        return
+    }
+    let number_of_swaps = nbytes / 2;
+    let mut offset = 0;
+    for i in 0..number_of_swaps {
+        unsafe {
+            src.offset(offset).copy_to(dest.offset(offset + 1), 1);
+            src.offset(offset + 1).copy_to(dest.offset(offset), 1);
+        }
+        offset += 2;
+    }
 }
 
 #[no_mangle]

tests/Makefile

@@ -81,6 +81,7 @@ EXPECT_BINS=\
 	unistd/pipe \
 	unistd/rmdir \
 	unistd/sleep \
+	unistd/swab \
 	unistd/write \
 	waitpid \
 	wchar/mbrtowc \

tests/unistd/swab.c

@@ -0,0 +1,51 @@
+#include <unistd.h>
+
+int main(int argc, char ** argv) {
+
+    const char source[] = {0, 1, 2, 3, 4, 5, 6};
+    char destination[] = {0, 0, 0, 0, 0, 0};
+    const char flipped_source[] = {1, 0, 3, 2, 5, 4};
+    const char first_two_source_bytes_flipped[] = {1, 0};
+
+    swab(source, destination, /* nbytes */ -3);
+    for (int i = 0; i < sizeof(destination); ++i) {
+        if (destination[i] != 0) {
+            puts("If nbytes is negative destionation shouldn't be modified");
+            return 1;
+        }
+    }
+
+    swab(source, destination, /* nbytes */ 0);
+    for (int i = 0; i < sizeof(destination); ++i) {
+        if (destination[i] != 0) {
+            puts("If nbytes is zero destionation shouldn't be modified");
+            return 1;
+        }
+    }
+
+    swab(source, destination, /* nbytes */ 3);
+    for (int i = 0; i < sizeof(first_two_source_bytes_flipped); ++i) {
+        if (destination[i] != first_two_source_bytes_flipped[i]) {
+            puts("copied bytes don't match expected values");
+            return 1;
+        }
+    }
+    // If nbytes is not even it's not specified what should happen to the
+    // last byte so the third byte in destination is not checked.
+    for (int i = sizeof(first_two_source_bytes_flipped) + 1; i < sizeof(destination); ++i) {
+        if (destination[i] != 0) {
+            puts("swab modified too many bytes in destination");
+            return 1;
+        }
+    }
+
+    swab(source, destination, /* nbytes */ sizeof(destination));
+    for (int i = 0; i < sizeof(destination); ++i) {
+        if (destination[i] != flipped_source[i]) {
+            puts("copied bytes don't match expected values");
+            return 1;
+        }
+    }
+
+    return 0;
+}