diff --git a/examples/euler4.zr b/examples/euler4.zr
new file mode 100644
index 0000000..454283a
--- /dev/null
+++ b/examples/euler4.zr
@@ -0,0 +1,23 @@
+func print_i64[x: I64] : I64
+    printf("%ld\n", x)
+
+func i64_to_string[n: I64] : String
+    let x: I64 = malloc(21)
+    sprintf(x, "%ld", n)
+    return x
+
+func main[] : I64
+    let out: I64 = 0
+
+    let a: I64 = 500
+    while a < 1000
+        let b: I64 = 500
+        while b < 1000
+            if a * b > out
+                let s: String = i64_to_string(a * b)
+                let s_rev: String = strrev(s)
+                if strcmp(s, s_rev) == 0
+                    out = a * b
+            b = b + 1
+        a = a + 1
+    print_i64(out)
\ No newline at end of file
diff --git a/src/codegen_x86_64.rs b/src/codegen_x86_64.rs
index a7e50fe..e1e4a70 100644
--- a/src/codegen_x86_64.rs
+++ b/src/codegen_x86_64.rs
@@ -100,8 +100,37 @@ extern free
 extern printf
 extern sprintf
 extern strlen
+extern strcmp
 extern puts
 print equ puts
+
+; generated with clang
+strrev:
+    push    r14
+    push    rbx
+    push    rax
+    mov     rbx, rdi
+    call    strlen
+    mov     r14, rax
+    lea     rdi, [rax + 1]
+    call    malloc
+    mov     rcx, rax
+    mov     rsi, r14
+    mov     rdx, r14
+.LBB0_1:
+    sub     rdx, 1
+    jb      .LBB0_2
+    mov     sil, byte [rbx + rsi - 1]
+    mov     byte [rcx], sil
+    inc     rcx
+    mov     rsi, rdx
+    jmp     .LBB0_1
+.LBB0_2:
+    mov     byte [rax + r14], 0
+    add     rsp, 8
+    pop     rbx
+    pop     r14
+    ret
 ",
         );
         Ok(())