add and test ByteLiteral abstraction

src/byte_literal.rs

@@ -0,0 +1,21 @@
+use crate::platform::types::c_char;
+
+pub struct ByteLiteral(u8);
+
+impl ByteLiteral {
+    pub fn cast_unchecked(input: u8) -> c_char {
+        match input {
+            b' '..=b'~' => {
+                #[cfg(any(target_arch = "x86_64", target_arch = "x86"))]
+                {
+                    input.cast_signed()
+                }
+                #[cfg(any(target_arch = "aarch64", target_arch = "riscv64"))]
+                {
+                    input.cast_unsigned()
+                }
+            },
+            _ => panic!("Not a printable ascii character!"),
+        }
+    }
+}

src/header/fmtmsg/mod.rs

@@ -6,6 +6,7 @@
 //! See <https://github.com/kraj/musl/blob/kraj/master/src/misc/fmtmsg.c>
 
 use crate::{
+    byte_literal::ByteLiteral,
     header::{
         fcntl::{O_WRONLY, open},
         pthread::{PTHREAD_CANCEL_DISABLE, pthread_setcancelstate},
@@ -77,7 +78,7 @@ unsafe fn strcolcmp(mut lstr: *const c_char, mut bstr: *const c_char) -> c_int {
             lstr = lstr.add(1);
             bstr = bstr.add(1);
         }
-        if *lstr != 0 || (*bstr != 0 && *bstr != b':'.cast_signed()) {
+        if *lstr != 0 || (*bstr != 0 && *bstr != ByteLiteral::cast_unchecked(b':')) {
             1
         } else {
             0

src/lib.rs

@@ -36,6 +36,7 @@ extern crate syscall;
 
 #[macro_use]
 mod macros;
+pub mod byte_literal;
 pub mod c_str;
 pub mod c_vec;
 pub mod cxa;