From a077ad3bc920e31abf9611a3c67fa6d4057aecea Mon Sep 17 00:00:00 2001
From: Trevor Spiteri <tspiteri@ieee.org>
Date: Fri, 10 Aug 2018 10:44:25 +0200
Subject: [PATCH] implement Sum and Product

---
 src/lib.rs    | 19 +++++++++++++++++++
 src/traits.rs | 25 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 668408f..ae1c520 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,6 +14,7 @@ mod traits;
 
 use std::f32;
 use std::f64;
+use std::iter::{Product, Sum};
 use std::mem;
 use std::ops::{
     Add, AddAssign, BitAnd, BitAndAssign, BitOr, BitOrAssign, BitXor, BitXorAssign, Div, DivAssign,
@@ -290,6 +291,24 @@ macro_rules! fixed_unsigned {
         pass_assign! { impl BitOrAssign for $Fixed($Inner) { bitor_assign } }
         pass! { impl BitXor for $Fixed($Inner) { bitxor } }
         pass_assign! { impl BitXorAssign for $Fixed($Inner) { bitxor_assign } }
+
+        impl Product<$Fixed> for $Fixed {
+            fn product<I: Iterator<Item = $Fixed>>(mut iter: I) -> $Fixed {
+                match iter.next() {
+                    None => <$Fixed as FixedNum>::one().expect("overflow"),
+                    Some(first) => iter.fold(first, Mul::mul),
+                }
+            }
+        }
+
+        impl<'a> Product<&'a $Fixed> for $Fixed {
+            fn product<I: Iterator<Item = &'a $Fixed>>(mut iter: I) -> $Fixed {
+                match iter.next() {
+                    None => <$Fixed as FixedNum>::one().expect("overflow"),
+                    Some(first) => iter.fold(*first, Mul::mul),
+                }
+            }
+        }
     };
 }
 
diff --git a/src/traits.rs b/src/traits.rs
index eba714b..bc6c754 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -8,6 +8,7 @@ use {
 
 pub(crate) trait FixedNum: Copy {
     type Part;
+    fn one() -> Option<Self>;
     fn parts(self) -> (bool, Self::Part, Self::Part);
     #[inline(always)]
     fn int_bits() -> u32 {
@@ -82,6 +83,18 @@ macro_rules! fixed_num_unsigned {
     ($Fixed:ident($Part:ty)) => {
         fixed_num_common! {
             $Fixed($Part);
+
+            #[inline]
+            fn one() -> Option<Self> {
+                let int_bits = <$Fixed as FixedNum>::int_bits();
+                let frac_bits = <$Fixed as FixedNum>::frac_bits();
+                if int_bits < 1 {
+                    None
+                } else {
+                    Some($Fixed::from_bits(1 << frac_bits))
+                }
+            }
+
             #[inline]
             fn parts(self) -> (bool, $Part, $Part) {
                 let bits = self.to_bits();
@@ -99,6 +112,18 @@ macro_rules! fixed_num_signed {
     ($Fixed:ident($Part:ty)) => {
         fixed_num_common! {
             $Fixed($Part);
+
+            #[inline]
+            fn one() -> Option<Self> {
+                let int_bits = <$Fixed as FixedNum>::int_bits();
+                let frac_bits = <$Fixed as FixedNum>::frac_bits();
+                if int_bits < 2 {
+                    None
+                } else {
+                    Some($Fixed::from_bits(1 << frac_bits))
+                }
+            }
+
             #[inline]
             fn parts(self) -> (bool, $Part, $Part) {
                 let bits = self.to_bits().wrapping_abs() as $Part;