Numtoa Optimization

- This update will ~double the performance of base 10 numtoa integer conversions.

src/misc/numtoa.rs

@@ -1,5 +1,19 @@
 use std::ptr::swap;
 
+/// Converts a number into a string representation, storing the conversion into a mutable byte slice.
+pub trait NumToA<T> {
+    /// Given a base for encoding and a mutable byte slice, write the number into the byte slice and return the
+    /// amount of bytes that were written.
+    ///
+    /// # Panics
+    /// If the supplied buffer is smaller than the number of bytes needed to write the integer, this will panic.
+    fn numtoa(self, base: T, string: &mut [u8]) -> usize;
+}
+
+// A lookup table to prevent the need for conditional branching
+// The value of the remainder of each step will be used as the index
+const LOOKUP: &'static [u8] = b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
 /// Because the integer to string conversion writes the representation in reverse, this will correct it.
 fn reverse(string: &mut [u8], length: usize) {
     let mut start = 0isize;
@@ -15,16 +29,42 @@ fn reverse(string: &mut [u8], length: usize) {
     }
 }
 
-/// Converts a number into a string representation, storing the conversion into a mutable byte slice.
-pub trait NumToA<T> {
-    /// Given a base for encoding and mutable byte slice, write the number into the byte slice and return the
-    /// amount of bytes that were written.
-    fn numtoa(self, base: T, string: &mut [u8]) -> usize;
-}
+macro_rules! base_10 {
+    ($number:ident, $index:ident, $string:ident) => {
+        // Decode four characters at the same time
+        while $number > 9999 {
+            let rem = $number % 10000;
+            $string[$index+3] = LOOKUP[(rem / 1000) as usize];
+            $string[$index+2] = LOOKUP[(rem % 1000 / 100) as usize];
+            $string[$index+1] = LOOKUP[(rem % 100 / 10) as usize];
+            $string[$index]   = LOOKUP[(rem % 10) as usize];
+            $index += 4;
+            $number /= 10000;
+        }
 
-// A lookup table to prevent the need for conditional branching
-// The value of the remainder of each step will be used as the index
-const LOOKUP: &'static [u8] = b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+        if $number > 999 {
+            let rem = $number % 1000;
+            $string[$index+3] = LOOKUP[($number / 1000) as usize];
+            $string[$index+2] = LOOKUP[(rem / 100) as usize];
+            $string[$index+1] = LOOKUP[(rem % 100 / 10) as usize];
+            $string[$index]   = LOOKUP[(rem % 10) as usize];
+            $index += 4;
+        } else if $number > 99 {
+            let rem = $number % 100;
+            $string[$index+2] = LOOKUP[($number / 100) as usize];
+            $string[$index+1] = LOOKUP[(rem / 10) as usize];
+            $string[$index]   = LOOKUP[(rem % 10) as usize];
+            $index += 3;
+        } else if $number > 9 {
+            $string[$index+1] = LOOKUP[($number / 10) as usize];
+            $string[$index]   = LOOKUP[($number % 10) as usize];
+            $index += 2;
+        } else {
+            $string[$index] = LOOKUP[$number as usize];
+            $index += 1;
+        }
+    }
+}
 
 macro_rules! impl_unsized_numtoa_for {
     ($t:ty) => {
@@ -36,11 +76,16 @@ macro_rules! impl_unsized_numtoa_for {
                 }
 
                 let mut index = 0;
-                while self != 0 {
-                    let rem = self % base;
-                    string[index] = LOOKUP[rem as usize];
-                    index += 1;
-                    self /= base;
+
+                if base == 10 {
+                    base_10!(self, index, string);
+                } else {
+                    while self != 0 {
+                        let rem = self % base;
+                        string[index] = LOOKUP[rem as usize];
+                        index += 1;
+                        self /= base;
+                    }
                 }
 
                 reverse(string, index);
@@ -65,11 +110,15 @@ macro_rules! impl_sized_numtoa_for {
                     return 1;
                 }
 
-                while self != 0 {
-                    let rem = self % base;
-                    string[index] = LOOKUP[rem as usize];
-                    index += 1;
-                    self /= base;
+                if base == 10 {
+                    base_10!(self, index, string);
+                } else {
+                    while self != 0 {
+                        let rem = self % base;
+                        string[index] = LOOKUP[rem as usize];
+                        index += 1;
+                        self /= base;
+                    }
                 }
 
                 if is_negative {
@@ -85,13 +134,61 @@ macro_rules! impl_sized_numtoa_for {
     }
 }
 
-impl_sized_numtoa_for!(i8);
 impl_sized_numtoa_for!(i16);
 impl_sized_numtoa_for!(i32);
 impl_sized_numtoa_for!(i64);
 impl_sized_numtoa_for!(isize);
-impl_unsized_numtoa_for!(u8);
 impl_unsized_numtoa_for!(u16);
 impl_unsized_numtoa_for!(u32);
 impl_unsized_numtoa_for!(u64);
 impl_unsized_numtoa_for!(usize);
+
+impl NumToA<i8> for i8 {
+    fn numtoa(mut self, base: i8, string: &mut [u8]) -> usize {
+        let mut index = 0;
+        let mut is_negative = false;
+
+        if self < 0 {
+            is_negative = true;
+            self = self.abs();
+        } else if self == 0 {
+            string[0] = b'0';
+            return 1;
+        }
+
+        while self != 0 {
+            let rem = self % base;
+            string[index] = LOOKUP[rem as usize];
+            index += 1;
+            self /= base;
+        }
+
+        if is_negative {
+            string[index] = b'-';
+            index += 1;
+        }
+
+        reverse(string, index);
+        index
+    }
+}
+
+impl NumToA<u8> for u8 {
+    fn numtoa(mut self, base: u8, string: &mut [u8]) -> usize {
+        if self == 0 {
+            string[0] = b'0';
+            return 1;
+        }
+
+        let mut index = 0;
+        while self != 0 {
+            let rem = self % base;
+            string[index] = LOOKUP[rem as usize];
+            index += 1;
+            self /= base;
+        }
+
+        reverse(string, index);
+        index
+    }
+}