diff --git a/src/mode/mod.rs b/src/mode/mod.rs
index 320d556..04f1f3d 100644
--- a/src/mode/mod.rs
+++ b/src/mode/mod.rs
@@ -1,5 +1,7 @@
 //! Functions for parsing and managing permissions
 mod parser;
+use core::ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign};
+
 pub use parser::{Parser, ParseError};
 
 pub fn get_umask() -> u32 {
@@ -23,3 +25,47 @@ pub enum Bit {
     OWrite = 0o2,
     OExec = 0o1,
 }
+
+impl BitAnd<u32> for Bit {
+    type Output = u32;
+
+    fn bitand(self, rhs: u32) -> Self::Output {
+        self as u32 & rhs
+    }
+}
+
+impl BitAnd<Bit> for u32 {
+    type Output = u32;
+
+    fn bitand(self, rhs: Bit) -> Self::Output {
+        self & rhs as u32
+    }
+}
+
+impl BitAndAssign<Bit> for u32 {
+    fn bitand_assign(&mut self, rhs: Bit) {
+        *self = *self & rhs;
+    }
+}
+
+impl BitOr<u32> for Bit {
+    type Output = u32;
+
+    fn bitor(self, rhs: u32) -> Self::Output {
+        self as u32 | rhs
+    }
+}
+
+impl BitOr<Bit> for u32 {
+    type Output = u32;
+
+    fn bitor(self, rhs: Bit) -> Self::Output {
+        self | rhs as u32
+    }
+}
+
+impl BitOrAssign<Bit> for u32 {
+    fn bitor_assign(&mut self, rhs: Bit) {
+        *self = *self | rhs;
+    }
+}
diff --git a/src/mode/parser.rs b/src/mode/parser.rs
index 2864d63..bcb030f 100644
--- a/src/mode/parser.rs
+++ b/src/mode/parser.rs
@@ -1,4 +1,4 @@
-use std::{error, fmt::Display, num::ParseIntError};
+use std::{error, fmt::Display, num::ParseIntError, ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign}};
 use super::{Bit, get_umask};
 
 #[derive(Debug, PartialEq)]
@@ -38,11 +38,39 @@ enum Who {
     Other = 0o1,
 }
 
+impl BitAnd<Who> for u32 {
+    type Output = u32;
+
+    fn bitand(self, rhs: Who) -> Self::Output {
+        self & rhs as u32
+    }
+}
+
+impl BitAndAssign<Who> for u32 {
+    fn bitand_assign(&mut self, rhs: Who) {
+        *self = *self & rhs;
+    }
+}
+
+impl BitOr<Who> for u32 {
+    type Output = u32;
+
+    fn bitor(self, rhs: Who) -> Self::Output {
+        self | rhs as u32
+    }
+}
+
+impl BitOrAssign<Who> for u32 {
+    fn bitor_assign(&mut self, rhs: Who) {
+        *self = *self | rhs;
+    }
+}
+
 pub struct Parser {
     mode: u32,
     op: Option<Op>,
     who: u32,
-    bits: Vec<Bit>,
+    bits: u32,
 }
 
 impl Default for Parser {
@@ -54,7 +82,7 @@ impl Default for Parser {
             mode,
             op: None,
             who: 0,
-            bits: vec![],
+            bits: 0,
         }
     }
 }
@@ -65,7 +93,7 @@ impl Parser {
             mode,
             op: None,
             who: 0,
-            bits: vec![],
+            bits: 0,
         }
     }
 
@@ -79,58 +107,61 @@ impl Parser {
     }
 
     fn add_who(&mut self, who: Who) -> Result<(), ParseError> {
-        if self.op.is_some() || !self.bits.is_empty() {
+        if self.op.is_some() || !self.bits == 0 {
             Err(ParseError::InvalidDigit)
         } else {
-            self.who |= who as u32;
+            self.who |= who;
             Ok(())
         }
     }
 
     fn set_op(&mut self, op: Op) -> Result<(), ParseError> {
-        if self.op.is_some() || !self.bits.is_empty() {
+        if self.op.is_some() || !self.bits == 0 {
             Err(ParseError::InvalidDigit)
         } else {
             self.op = Some(op);
+            if self.who == 0 {
+                self.who |= 0o111;
+            }
             Ok(())
         }
     }
 
     fn push_read_bits(&mut self) -> Result<(), ParseError> {
         if self.who & 0o100 != 0 {
-            self.bits.push(Bit::URead);
+            self.bits |= Bit::URead;
         }
         if self.who & 0o10 != 0 {
-            self.bits.push(Bit::GRead);
+            self.bits |= Bit::GRead;
         }
         if self.who & 0o1 != 0 {
-            self.bits.push(Bit::ORead);
+            self.bits |= Bit::ORead;
         }
         Ok(())
     }
 
     fn push_write_bits(&mut self) -> Result<(), ParseError> {
         if self.who & 0o100 != 0 {
-            self.bits.push(Bit::UWrite);
+            self.bits |= Bit::UWrite;
         }
         if self.who & 0o10 != 0 {
-            self.bits.push(Bit::GWrite);
+            self.bits |= Bit::GWrite;
         }
         if self.who & 0o1 != 0 {
-            self.bits.push(Bit::OWrite);
+            self.bits |= Bit::OWrite;
         }
         Ok(())
     }
 
     fn push_exec_bits(&mut self) -> Result<(), ParseError> {
         if self.who & 0o100 != 0 {
-            self.bits.push(Bit::UExec);
+            self.bits |= Bit::UExec;
         }
         if self.who & 0o10 != 0 {
-            self.bits.push(Bit::GExec);
+            self.bits |= Bit::GExec;
         }
         if self.who & 0o1 != 0 {
-            self.bits.push(Bit::OExec);
+            self.bits |= Bit::OExec;
         }
         Ok(())
     }
@@ -140,10 +171,10 @@ impl Parser {
             return Err(ParseError::InvalidBit);
         }
         if self.who & 0o100 != 0 {
-            self.bits.push(Bit::Suid);
+            self.bits |= Bit::Suid;
         }
         if self.who &0o10 != 0 {
-            self.bits.push(Bit::Sgid);
+            self.bits |= Bit::Sgid;
         }
         Ok(())
     }
@@ -153,21 +184,17 @@ impl Parser {
             return Err(ParseError::InvalidBit);
         }
         if self.who & 0o1 != 0 {
-            self.bits.push(Bit::Sticky);
+            self.bits |= Bit::Sticky;
         }
         Ok(())
     }
 
     fn add_bits(&mut self) {
-        for bit in &self.bits {
-            self.mode |= *bit as u32;
-        }
+        self.mode |= self.bits;
     }
 
     fn remove_bits(&mut self) {
-        for bit in &self.bits {
-            self.mode &= !(*bit as u32);
-        }
+        self.mode &= !self.bits;
     }
 
     fn set_bits(&mut self) -> Result<(), ParseError> {
@@ -176,13 +203,13 @@ impl Parser {
             Some(Op::Remove) => self.remove_bits(),
             Some(Op::Equals) => {
                 if self.who & 0o100 != 0 {
-                    self.mode &= 0o4444;
+                    self.mode &= !(0o4700);
                 }
                 if self.who & 0o10 != 0 {
-                    self.mode &= 0o2222;
+                    self.mode &= !(0o2070);
                 }
                 if self.who &0o1 != 0 {
-                    self.mode &= 0o1111;
+                    self.mode &= !(0o1007);
                 }
                 self.add_bits();
             },
@@ -194,7 +221,7 @@ impl Parser {
     fn reset(&mut self) {
         self.who = 0;
         self.op = None;
-        self.bits.clear();
+        self.bits = 0;
     }
 
     pub fn mode(&self) -> u32 {
@@ -229,23 +256,17 @@ impl Parser {
                 'x' => self.push_exec_bits()?,
                 's' => self.push_suid_sgid()?,
                 't' => self.push_sticky()?,
+                ',' => {
+                    self.set_bits()?;
+                    self.reset();
+                },
                 _ => return Err(ParseError::InvalidDigit),
             }
         }
-        if self.who == 0 {
-            self.who |= 0o111;
-        }
         self.set_bits()?;
         self.reset();
         Ok(self.mode)
     }
-
-    pub fn parse_all(&mut self, value: &str) -> Result<u32, ParseError> {
-        for seg in value.split(',') {
-            let _mode = self.parse(seg);
-        }
-        Ok(self.mode())
-    }
 }
 
 #[cfg(test)]
@@ -279,4 +300,53 @@ mod test {
         let mode = parser.parse("ugo=rw");
         assert_eq!(mode, Ok(0o666));
     }
+
+    #[test]
+    fn o_equals() {
+        let mut parser = Parser::new(0o752);
+        let mode = parser.parse("o=rx");
+        assert_eq!(mode, Ok(0o755));
+    }
+
+    #[test]
+    fn empty_who() {
+        let mut parser = Parser::new(0o644);
+        let mode = parser.parse("+x");
+        assert_eq!(mode, Ok(0o755));
+    }
+
+    #[test]
+    fn compound_ops() {
+        let mut parser = Parser::new(0o666);
+        let mode = parser.parse("u+x,g-w,o-r");
+        assert_eq!(mode, Ok(0o742));
+    }
+
+    #[test]
+    fn compount_ops2() {
+        let mut parser = Parser::new(0o4444);
+        let mode = parser.parse("u+w,ug+x,o=rx,u-s");
+        assert_eq!(mode, Ok(0o755));
+    }
+
+    #[test]
+    fn invalid_sticky_bit() {
+        let mut parser = Parser::default();
+        let mode = parser.parse("u+t");
+        assert_eq!(mode, Err(ParseError::InvalidBit));
+    }
+
+    #[test]
+    fn invalid_s() {
+        let mut parser = Parser::default();
+        let mode = parser.parse("+s");
+        assert_eq!(mode, Err(ParseError::InvalidBit));
+    }
+
+    #[test]
+    fn outside_range() {
+        let mut parser = Parser::default();
+        let mode = parser.parse("10000");
+        assert_eq!(mode, Err(ParseError::OutsideRange))
+    }
 }