use unchecked type conversions

this is safe because we already checked their bit size

bitstream_reader_derive/src/lib.rs

@@ -138,7 +138,6 @@ extern crate proc_macro;
 use proc_macro2::{Span, TokenStream};
 use quote::{quote, quote_spanned};
 use syn::spanned::Spanned;
-use syn::token::Token;
 use syn::{
     parse_macro_input, parse_quote, parse_str, Attribute, Data, DeriveInput, Expr, Fields, Ident,
     Lit, LitStr, Meta, Pat, Path,

src/buffer.rs

@@ -9,6 +9,7 @@ use num_traits::{Float, PrimInt};
 
 use crate::endianness::Endianness;
 use crate::is_signed::IsSigned;
+use crate::unchecked_primitive::{UncheckedPrimitiveFloat, UncheckedPrimitiveInt};
 use crate::{ReadError, Result};
 
 const USIZE_SIZE: usize = size_of::<usize>();
@@ -192,7 +193,7 @@ where
     /// [`ReadError::TooManyBits`]: enum.ReadError.html#variant.TooManyBits
     pub fn read_int<T>(&self, position: usize, count: usize) -> Result<T>
     where
-        T: PrimInt + BitOrAssign + IsSigned,
+        T: PrimInt + BitOrAssign + IsSigned + UncheckedPrimitiveInt,
     {
         let value = {
             let type_bit_size = size_of::<T>() * 8;
@@ -210,9 +211,9 @@ where
                 let raw = self.read_usize(position, count)?;
                 let max_signed_value = (1 << (type_bit_size - 1)) - 1;
                 if T::is_signed() && raw > max_signed_value {
-                    return Ok(T::zero() - T::from(raw & max_signed_value).unwrap());
+                    return Ok(T::zero() - T::from_unchecked(raw & max_signed_value));
                 } else {
-                    T::from(raw).unwrap()
+                    T::from_unchecked(raw)
                 }
             } else {
                 let mut left_to_read = count;
@@ -223,7 +224,7 @@ where
                 while left_to_read > 0 {
                     let bits_left = self.bit_len - read_pos;
                     let read = min(min(left_to_read, max_read), bits_left);
-                    let data = T::from(self.read_usize(read_pos, read)?).unwrap();
+                    let data = T::from_unchecked(self.read_usize(read_pos, read)?);
                     if E::is_le() {
                         partial |= data << bit_offset;
                     } else {
@@ -400,14 +401,18 @@ where
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn read_float<T>(&self, position: usize) -> Result<T>
     where
-        T: Float,
+        T: Float + UncheckedPrimitiveFloat,
     {
         if size_of::<T>() == 4 {
-            let int = self.read_int::<u32>(position, 32)?;
-            Ok(T::from(f32::from_bits(int)).unwrap())
+            let int = if size_of::<T>() < USIZE_SIZE {
+                self.read_usize(position, 32)? as u32
+            } else {
+                self.read_int::<u32>(position, 32)?
+            };
+            Ok(T::from_f32_unchecked(f32::from_bits(int)))
         } else {
             let int = self.read_int::<u64>(position, 64)?;
-            Ok(T::from(f64::from_bits(int)).unwrap())
+            Ok(T::from_f64_unchecked(f64::from_bits(int)))
         }
     }
 }

src/lib.rs

@@ -74,6 +74,7 @@ mod endianness;
 mod is_signed;
 mod read;
 mod stream;
+mod unchecked_primitive;
 
 /// Errors that can be returned when trying to read from a buffer
 #[derive(Debug)]

src/stream.rs

@@ -6,6 +6,7 @@ use num_traits::{Float, PrimInt};
 
 use crate::endianness::Endianness;
 use crate::is_signed::IsSigned;
+use crate::unchecked_primitive::{UncheckedPrimitiveFloat, UncheckedPrimitiveInt};
 use crate::BitBuffer;
 use crate::{BitRead, BitReadSized, ReadError, Result};
 
@@ -143,7 +144,7 @@ where
     /// [`ReadError::TooManyBits`]: enum.ReadError.html#variant.TooManyBits
     pub fn read_int<T>(&mut self, count: usize) -> Result<T>
     where
-        T: PrimInt + BitOrAssign + IsSigned,
+        T: PrimInt + BitOrAssign + IsSigned + UncheckedPrimitiveInt,
     {
         self.verify_bits_left(count)?;
         let result = self.buffer.read_int(self.pos, count);
@@ -181,7 +182,7 @@ where
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn read_float<T>(&mut self) -> Result<T>
     where
-        T: Float,
+        T: Float + UncheckedPrimitiveFloat,
     {
         let count = size_of::<T>() * 8;
         self.verify_bits_left(count)?;

src/unchecked_primitive.rs

@@ -0,0 +1,179 @@
+/// Allow casting floats unchecked
+pub trait UncheckedPrimitiveFloat: Sized {
+    fn from_f32_unchecked(n: f32) -> Self;
+    fn from_f64_unchecked(n: f64) -> Self;
+}
+
+impl UncheckedPrimitiveFloat for f32 {
+    #[inline(always)]
+    fn from_f32_unchecked(n: f32) -> Self {
+        n
+    }
+    #[inline(always)]
+    fn from_f64_unchecked(n: f64) -> Self {
+        n as f32
+    }
+}
+
+impl UncheckedPrimitiveFloat for f64 {
+    #[inline(always)]
+    fn from_f32_unchecked(n: f32) -> Self {
+        n as f64
+    }
+    #[inline(always)]
+    fn from_f64_unchecked(n: f64) -> Self {
+        n
+    }
+}
+
+/// Allow casting integers unchecked
+pub trait UncheckedPrimitiveInt: Sized {
+    fn from_u8_unchecked(n: u8) -> Self;
+    fn from_i8_unchecked(n: i8) -> Self;
+    fn from_u16_unchecked(n: u16) -> Self;
+    fn from_i16_unchecked(n: i16) -> Self;
+    fn from_u32_unchecked(n: u32) -> Self;
+    fn from_i32_unchecked(n: i32) -> Self;
+    fn from_u64_unchecked(n: u64) -> Self;
+    fn from_i64_unchecked(n: i64) -> Self;
+    fn from_u128_unchecked(n: u128) -> Self;
+    fn from_i128_unchecked(n: i128) -> Self;
+    fn from_usize_unchecked(n: usize) -> Self;
+    fn from_isize_unchecked(n: isize) -> Self;
+
+    fn into_u8_unchecked(self) -> u8;
+    fn into_i8_unchecked(self) -> i8;
+    fn into_u16_unchecked(self) -> u16;
+    fn into_i16_unchecked(self) -> i16;
+    fn into_u32_unchecked(self) -> u32;
+    fn into_i32_unchecked(self) -> i32;
+    fn into_u64_unchecked(self) -> u64;
+    fn into_i64_unchecked(self) -> i64;
+    fn into_u128_unchecked(self) -> u128;
+    fn into_i128_unchecked(self) -> i128;
+    fn into_usize_unchecked(self) -> usize;
+    fn into_isize_unchecked(self) -> isize;
+
+    fn from_unchecked<N: UncheckedPrimitiveInt>(n: N) -> Self;
+}
+
+macro_rules! impl_unchecked_int {
+    ($type:ty, $conv:ident) => {
+        impl UncheckedPrimitiveInt for $type {
+            #[inline(always)]
+            fn from_u8_unchecked(n: u8) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_i8_unchecked(n: i8) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_u16_unchecked(n: u16) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_i16_unchecked(n: i16) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_u32_unchecked(n: u32) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_i32_unchecked(n: i32) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_u64_unchecked(n: u64) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_i64_unchecked(n: i64) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_u128_unchecked(n: u128) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_i128_unchecked(n: i128) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_usize_unchecked(n: usize) -> Self {
+                n as $type
+            }
+            #[inline(always)]
+            fn from_isize_unchecked(n: isize) -> Self {
+                n as $type
+            }
+
+            fn into_u8_unchecked(self) -> u8 {
+                self as u8
+            }
+            #[inline(always)]
+            fn into_i8_unchecked(self) -> i8 {
+                self as i8
+            }
+            #[inline(always)]
+            fn into_u16_unchecked(self) -> u16 {
+                self as u16
+            }
+            #[inline(always)]
+            fn into_i16_unchecked(self) -> i16 {
+                self as i16
+            }
+            #[inline(always)]
+            fn into_u32_unchecked(self) -> u32 {
+                self as u32
+            }
+            #[inline(always)]
+            fn into_i32_unchecked(self) -> i32 {
+                self as i32
+            }
+            #[inline(always)]
+            fn into_u64_unchecked(self) -> u64 {
+                self as u64
+            }
+            #[inline(always)]
+            fn into_i64_unchecked(self) -> i64 {
+                self as i64
+            }
+            #[inline(always)]
+            fn into_u128_unchecked(self) -> u128 {
+                self as u128
+            }
+            #[inline(always)]
+            fn into_i128_unchecked(self) -> i128 {
+                self as i128
+            }
+            #[inline(always)]
+            fn into_usize_unchecked(self) -> usize {
+                self as usize
+            }
+            #[inline(always)]
+            fn into_isize_unchecked(self) -> isize {
+                self as isize
+            }
+
+            #[inline(always)]
+            fn from_unchecked<N: UncheckedPrimitiveInt>(n: N) -> Self {
+                n.$conv()
+            }
+        }
+    };
+}
+
+impl_unchecked_int!(u8, into_u8_unchecked);
+impl_unchecked_int!(i8, into_i8_unchecked);
+impl_unchecked_int!(u16, into_u16_unchecked);
+impl_unchecked_int!(i16, into_i16_unchecked);
+impl_unchecked_int!(u32, into_u32_unchecked);
+impl_unchecked_int!(i32, into_i32_unchecked);
+impl_unchecked_int!(u64, into_u64_unchecked);
+impl_unchecked_int!(i64, into_i64_unchecked);
+impl_unchecked_int!(u128, into_u128_unchecked);
+impl_unchecked_int!(i128, into_i128_unchecked);
+impl_unchecked_int!(usize, into_usize_unchecked);
+impl_unchecked_int!(isize, into_isize_unchecked);

tests/tests.rs

@@ -1,11 +1,17 @@
-use bitstream_reader::{BigEndian, BitBuffer, BitRead, BitStream, LittleEndian};
-use maplit::hashmap;
-use std::collections::HashMap;
+//#![feature(test)]
 
+// for bench on nightly
+//extern crate test;
+
+use std::collections::HashMap;
 // for bench on nightly
 //use std::fs;
 //use test::Bencher;
 
+use maplit::hashmap;
+
+use bitstream_reader::{BigEndian, BitBuffer, BitRead, BitStream, LittleEndian};
+
 const BYTES: &'static [u8] = &[
     0b1011_0101,
     0b0110_1010,
@@ -372,7 +378,7 @@ fn test_read_struct() {
 //    0b1110_0111,
 
 // for bench on nightly
-//fn read_perf<P: IsPadded>(buffer: BitBuffer<LittleEndian, P>) -> u16 {
+//fn read_perf(buffer: &BitBuffer<LittleEndian>) -> u16 {
 //    let size = 5;
 //    let mut pos = 0;
 //    let len = buffer.bit_len();
@@ -386,6 +392,7 @@ fn test_read_struct() {
 //        pos += size;
 //    }
 //}
+
 //
 //#[bench]
 //fn perf_padded(b: &mut Bencher) {
@@ -404,10 +411,9 @@ fn test_read_struct() {
 //#[bench]
 //fn perf_non_padded(b: &mut Bencher) {
 //    let file = fs::read("/bulk/tmp/test.dem").expect("Unable to read file");
-//    let bytes = file.as_slice();
+//    let buffer = BitBuffer::new(file, LittleEndian);
 //    b.iter(|| {
-//        let buffer = BitBuffer::new(&bytes, LittleEndian);
-//        let data = read_perf(buffer);
+//        let data = read_perf(&buffer);
 //        assert_eq!(data, 43943);
 //        test::black_box(data);
 //    });