diff --git a/fcmprs/Cargo.toml b/fcmprs/Cargo.toml
index 0e27425..6f06b50 100644
--- a/fcmprs/Cargo.toml
+++ b/fcmprs/Cargo.toml
@@ -7,3 +7,6 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+memmap = "0.7.0"
+rayon = "1.5.0"
+smallvec = "1.5.0"
diff --git a/fcmprs/src/error.rs b/fcmprs/src/error.rs
new file mode 100644
index 0000000..c4041dc
--- /dev/null
+++ b/fcmprs/src/error.rs
@@ -0,0 +1,20 @@
+
+
+pub trait ResultPrintExt<T>
+{
+    fn discard_msg(self, msg: impl AsRef<str>) -> Option<T>;
+}
+
+impl<T, E> ResultPrintExt<T> for Result<T,E>
+    where E: std::fmt::Display
+{
+    fn discard_msg(self, msg: impl AsRef<str>) -> Option<T> {
+	match self {
+	    Ok(v) => Some(v),
+	    Err(e) => {
+		eprintln!("{}: {}", msg.as_ref(), e);
+		None
+	    },
+	}
+    }
+}
diff --git a/fcmprs/src/main.rs b/fcmprs/src/main.rs
index e7a11a9..4292a95 100644
--- a/fcmprs/src/main.rs
+++ b/fcmprs/src/main.rs
@@ -1,3 +1,61 @@
+use rayon::prelude::*;
+use std::{
+    path::Path,
+    io, fs::{self, OpenOptions,},
+};
+use smallvec::SmallVec;
+
+fn usage() -> !
+{
+    eprintln!("fcmprs: Compare files for identity");
+    eprintln!("Usage: {} <files...>", std::env::args().next().unwrap());
+
+    std::process::exit(-1)
+}
+
+mod error;
+use error::ResultPrintExt as _;
+
+mod map;
+
 fn main() {
-    println!("Hello, world!");
+    let (map1, rest) = {	
+	let mut args = std::env::args().skip(1);
+	if let Some(one) = args.next() {
+	    (one, args)
+	} else {
+	    usage();
+	}
+    };
+
+    std::process::exit(dbg!(if let Some(map1) = map::map(&map1).discard_msg(format!("Failed to map file {}", map1)) {
+	let slice = map1.as_slice();
+	let mut ok = true;
+	let chk: SmallVec<[_; 32]> = rest.filter_map(|filename| {
+	    let path = Path::new(&filename);
+	    if path.exists() && path.is_file() {
+		map::map(path).discard_msg(format!("Failed to map file {}", filename))
+		    .or_else(|| { ok = false; None })
+	    } else {
+		eprintln!("File {} does not exist or is not a normal file", filename);
+		ok = false;
+		None
+	    }
+	}).collect();
+
+	if !ok {
+	    -1
+	} else {
+	    match chk.into_par_iter()
+		.map(|map| slice == map.as_slice())
+		.reduce_with(|x, y| x && y)
+	    {
+		Some(true) => 0,
+		Some(false) => 1,
+		None => usage(),
+	    }
+	}
+    } else {
+	-1
+    }))
 }
diff --git a/fcmprs/src/map.rs b/fcmprs/src/map.rs
new file mode 100644
index 0000000..6e8e5c6
--- /dev/null
+++ b/fcmprs/src/map.rs
@@ -0,0 +1,30 @@
+use super::*;
+
+/// Represents an open and memory mapped file
+#[derive(Debug)]
+pub struct MemMap
+{
+    map: memmap::Mmap,
+    file: fs::File,
+}
+
+impl MemMap
+{
+    /// Get the memory mapped portion as a slice
+    #[inline] pub fn as_slice(&self) -> &[u8]
+    {
+	&self.map[..]
+    }
+}
+
+/// Attempt to map this file
+pub fn map(file: impl AsRef<Path>) -> io::Result<MemMap>
+{
+    let file = OpenOptions::new()
+        .read(true)
+        .open(file)?;
+    Ok(MemMap {
+	map: unsafe { memmap::Mmap::map(&file)? },
+	file,
+    })
+}