uptime: optimize uptime calculation w/ inline assembly and custom itoa

lol, lmao even.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Ie22fbd2e9c2be5740b493bdc81caafb36a6a6964

src/uptime.rs

@@ -1,4 +1,66 @@
-use std::{fmt::Write, io, mem::MaybeUninit};
+use std::{io, mem::MaybeUninit};
+
+/// Fast integer to string conversion (no formatting overhead)
+#[inline]
+fn itoa(mut n: u64, buf: &mut [u8]) -> &str {
+  if n == 0 {
+    return "0";
+  }
+
+  let mut i = buf.len();
+  while n > 0 {
+    i -= 1;
+    buf[i] = b'0' + (n % 10) as u8;
+    n /= 10;
+  }
+
+  unsafe { std::str::from_utf8_unchecked(&buf[i..]) }
+}
+
+/// Direct sysinfo syscall using inline assembly
+///
+/// # Safety
+/// This function uses inline assembly to make a direct syscall.
+/// The caller must ensure the sysinfo pointer is valid.
+#[inline]
+unsafe fn sys_sysinfo(info: *mut libc::sysinfo) -> i64 {
+  #[cfg(target_arch = "x86_64")]
+  {
+    let ret: i64;
+    unsafe {
+      std::arch::asm!(
+        "syscall",
+        in("rax") 99_i64, // __NR_sysinfo
+        in("rdi") info,
+        out("rcx") _,
+        out("r11") _,
+        lateout("rax") ret,
+        options(nostack)
+      );
+    }
+    ret
+  }
+
+  #[cfg(target_arch = "aarch64")]
+  {
+    let ret: i64;
+    unsafe {
+      std::arch::asm!(
+        "svc #0",
+        in("x8") 179_i64, // __NR_sysinfo
+        in("x0") info,
+        lateout("x0") ret,
+        options(nostack)
+      );
+    }
+    ret
+  }
+
+  #[cfg(not(any(target_arch = "x86_64", target_arch = "aarch64")))]
+  {
+    unsafe { libc::sysinfo(info) as i64 }
+  }
+}
 
 /// Gets the current system uptime.
 ///
@@ -9,7 +71,7 @@ use std::{fmt::Write, io, mem::MaybeUninit};
 pub fn get_current() -> Result<String, io::Error> {
   let uptime_seconds = {
     let mut info = MaybeUninit::uninit();
-    if unsafe { libc::sysinfo(info.as_mut_ptr()) } != 0 {
+    if unsafe { sys_sysinfo(info.as_mut_ptr()) } != 0 {
       return Err(io::Error::last_os_error());
     }
     #[allow(clippy::cast_sign_loss)]
@@ -23,22 +85,24 @@ pub fn get_current() -> Result<String, io::Error> {
   let minutes = (uptime_seconds / 60) % 60;
 
   let mut result = String::with_capacity(32);
+  let mut buf = [0u8; 20]; // Enough for u64::MAX
+
   if days > 0 {
-    let _ = write!(result, "{days}");
+    result.push_str(itoa(days, &mut buf));
     result.push_str(if days == 1 { " day" } else { " days" });
   }
   if hours > 0 {
     if !result.is_empty() {
       result.push_str(", ");
     }
-    let _ = write!(result, "{hours}");
+    result.push_str(itoa(hours, &mut buf));
     result.push_str(if hours == 1 { " hour" } else { " hours" });
   }
   if minutes > 0 {
     if !result.is_empty() {
       result.push_str(", ");
     }
-    let _ = write!(result, "{minutes}");
+    result.push_str(itoa(minutes, &mut buf));
     result.push_str(if minutes == 1 { " minute" } else { " minutes" });
   }
   if result.is_empty() {