Support no_std

Fixes #3.

Cargo.toml

@@ -11,4 +11,6 @@ readme = "README.md"
 exclude = ["performance.png"]
 
 [features]
+default = ["use_std"]
 i128 = []
+use_std = []

README.md

@@ -53,6 +53,9 @@ where `itoa::Integer` is implemented for `i8`, `u8`, `i16`, `u16`, `i32`, `u32`,
 only available with the nightly compiler when the `i128` feature is enabled for
 this crate. The return value gives the number of bytes written.
 
+The `write` function is only available when the `use_std` feature is enabled
+(default is enabled).
+
 ## Dependency
 
 Itoa is available on [crates.io](https://crates.io/crates/itoa). Use the

src/lib.rs

@@ -8,15 +8,22 @@
 
 #![doc(html_root_url = "https://docs.rs/itoa/0.3.4")]
 
+#![cfg_attr(not(feature = "use_std"), no_std)]
+
 #![cfg_attr(feature = "i128", feature(i128_type, i128))]
 
 #![cfg_attr(feature = "cargo-clippy", allow(cast_lossless, unreadable_literal))]
 
 #[cfg(feature = "i128")]
 mod udiv128;
 
+#[cfg(feature = "use_std")]
 use std::{fmt, io, mem, ptr, slice, str};
 
+#[cfg(not(feature = "use_std"))]
+use core::{fmt, mem, ptr, slice, str};
+
+#[cfg(feature = "use_std")]
 #[inline]
 pub fn write<W: io::Write, V: Integer>(wr: W, value: V) -> io::Result<usize> {
     value.write(wr)
@@ -28,6 +35,7 @@ pub fn fmt<W: fmt::Write, V: Integer>(wr: W, value: V) -> fmt::Result {
 }
 
 pub trait Integer {
+    #[cfg(feature = "use_std")]
     fn write<W: io::Write>(self, W) -> io::Result<usize>;
 
     fn fmt<W: fmt::Write>(self, W) -> fmt::Result;
@@ -51,6 +59,7 @@ const MAX_LEN: usize = 40; // i128::MIN (including minus sign)
 macro_rules! impl_IntegerCommon {
     ($t:ident) => {
         impl Integer for $t {
+            #[cfg(feature = "use_std")]
             fn write<W: io::Write>(self, mut wr: W) -> io::Result<usize> {
                 let mut buf = unsafe { mem::uninitialized() };
                 let bytes = self.write_to(&mut buf);

tests/test.rs

@@ -17,9 +17,12 @@ macro_rules! test {
             $(#[$attr])*
             #[test]
             fn $name() {
-                let mut buf = [b'\0'; 40];
-                let len = itoa::write(&mut buf[..], $value).unwrap();
-                assert_eq!(&buf[0..len], $expected.as_bytes());
+                #[cfg(feature = "use_std")]
+                {
+                    let mut buf = [b'\0'; 40];
+                    let len = itoa::write(&mut buf[..], $value).unwrap();
+                    assert_eq!(&buf[0..len], $expected.as_bytes());
+                }
 
                 let mut s = String::new();
                 itoa::fmt(&mut s, $value).unwrap();