Make the crate #![no_std] (#79)

https://effective-rust.com/no-std.html says:

> So: if your dependencies support it, and the simple transformations
above are all that's needed, then **consider making library code no_std
compatible**. When it is possible, it's not much additional work, and it
allows for the widest reuse of the library.

Code changes are minimal, we don't need a `std` feature because nothing
will be disabled without it. `alloc` is definitely required for
Frame/Plane/AlignedData but that's still a smaller hurdle than the
entire standard library.

`println` is now off the table for tests but that's not really a big
limitation IMHO.

Author: FreezyLemon

README.md

@@ -14,6 +14,7 @@
 - **Support for common subsampling formats**: YUV 4:2:0, 4:2:2, 4:4:4, and monochrome
 - **Performant API**: Efficient row-based and pixel-based data access
 - **SIMD-friendly data alignment**: Plane data is aligned to at least 64 bytes on most targets
+- **`no_std` support**: Does not depend on the standard library (`alloc` is required however)
 - **WebAssembly support**: Works in both browser (`wasm32-unknown-unknown`) and WASI environments
 
 ## Installation
@@ -85,6 +86,12 @@ for pixel_row in frame.y_plane.rows() {
 }
 ```
 
+## `no_std` support
+
+This crate does not depend on the standard library `std` but does require `alloc` to allocate memory for `Plane<T>` data.
+
+Users linking against `std` don't have to do anything. If you want to use this crate without `std`, you need to setup and configure a global allocator. The [Embedded Rust Book](https://docs.rust-embedded.org/book/collections/index.html#using-alloc) might be helpful.
+
 ## WebAssembly Support
 
 v_frame works in WebAssembly environments:

src/chroma.rs

@@ -56,7 +56,7 @@
 #[cfg(test)]
 mod tests;
 
-use std::num::NonZeroU8;
+use core::num::NonZeroU8;
 
 /// Specifies the chroma subsampling for a YUV frame.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]

src/chroma/tests.rs

@@ -10,7 +10,7 @@
 #![allow(clippy::unwrap_used, reason = "test file")]
 
 use super::*;
-use std::num::NonZeroU8;
+use core::num::NonZeroU8;
 
 #[test]
 fn has_chroma() {

src/frame.rs

@@ -81,7 +81,7 @@ pub use error::FrameError;
 #[cfg(test)]
 mod tests;
 
-use std::num::NonZeroU8;
+use core::num::NonZeroU8;
 
 use crate::{
     chroma::ChromaSubsampling,

src/frame/error.rs

@@ -7,7 +7,7 @@
 // Media Patent License 1.0 was not distributed with this source code in the
 // PATENTS file, you can obtain it at www.aomedia.org/license/patent.
 
-use std::fmt;
+use core::fmt;
 
 /// This enum represents all possible error conditions that can occur during
 /// frame creation, including data validation errors, unsupported formats,
@@ -52,4 +52,4 @@ impl fmt::Display for FrameError {
     }
 }
 
-impl std::error::Error for FrameError {}
+impl core::error::Error for FrameError {}

src/frame/tests.rs

@@ -12,6 +12,8 @@
 use super::*;
 use crate::chroma::ChromaSubsampling;
 
+use alloc::format;
+
 #[test]
 fn plane_access() {
     let mut frame = FrameBuilder::new(1920, 1080, ChromaSubsampling::Yuv420, 8)

src/lib.rs

@@ -33,6 +33,10 @@
 //!     .unwrap();
 //! ```
 
+#![no_std]
+
+extern crate alloc;
+
 pub mod chroma;
 pub mod frame;
 pub mod pixel;

src/plane.rs

@@ -42,7 +42,7 @@ pub use error::CopyError;
 mod tests;
 
 #[cfg(feature = "padding_api")]
-use std::mem::MaybeUninit;
+use core::mem::MaybeUninit;
 
 mod aligned;
 use aligned::AlignedData;

src/plane/aligned.rs

@@ -1,9 +1,11 @@
-use std::alloc::{Layout, alloc, alloc_zeroed, dealloc, handle_alloc_error};
-use std::fmt::Debug;
-use std::marker::PhantomData;
-use std::mem::{ManuallyDrop, MaybeUninit, align_of};
-use std::ops::{Deref, DerefMut};
-use std::ptr::NonNull;
+use alloc::alloc::{alloc, alloc_zeroed, dealloc, handle_alloc_error};
+
+use core::alloc::Layout;
+use core::fmt::{self, Debug};
+use core::marker::PhantomData;
+use core::mem::{ManuallyDrop, MaybeUninit};
+use core::ops::{Deref, DerefMut};
+use core::ptr::NonNull;
 
 use crate::pixel::Pixel;
 
@@ -148,7 +150,7 @@ impl<T: PartialEq<U>, U> PartialEq<AlignedData<U>> for AlignedData<T> {
 impl<T: Eq> Eq for AlignedData<T> {}
 
 impl<T: Debug> Debug for AlignedData<T> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         if self.len() > 5 {
             f.debug_list().entries(&self[..5]).finish_non_exhaustive()
         } else {
@@ -209,6 +211,8 @@ impl<T> Drop for AlignedData<T> {
 mod tests {
     use super::*;
 
+    use alloc::{format, string::String, vec::Vec};
+
     #[test]
     fn empty() {
         AlignedData::<u8>::new(0);
@@ -295,19 +299,24 @@ mod tests {
 
         // SAFETY: Initialized above.
         let data = unsafe { data.assume_init() };
-        println!("{:?}", &data[100..140]);
+        for (idx, x) in data[100..140].iter().enumerate() {
+            let idx = 100 + idx;
+            assert_eq!(*x, (idx % 42) as u8);
+        }
     }
 
     #[test]
     fn uninit_with_drop() {
         let mut data = AlignedData::<String>::new_uninit(3);
-        data[0].write("Hello World".into());
+        data[0].write(String::from("Hello World"));
         data[1].write(String::new());
-        data[2].write("This is a test".into());
+        data[2].write(String::from("This is a test"));
 
         // SAFETY: Initialized above.
         let data = unsafe { data.assume_init() };
-        println!("{:?}", &*data);
+        assert_eq!(data[0], String::from("Hello World"));
+        assert_eq!(data[1], String::new());
+        assert_eq!(data[2], String::from("This is a test"));
     }
 
     #[test]
@@ -374,14 +383,16 @@ mod tests {
     #[test]
     fn clone() {
         let mut data = AlignedData::<String>::new_uninit(3);
-        data[0].write("Hello World".into());
+        data[0].write(String::from("Hello World"));
         data[1].write(String::new());
-        data[2].write("This is a test".into());
+        data[2].write(String::from("This is a test"));
 
         // SAFETY: Initialized above.
         let data = unsafe { data.assume_init() };
         let data2 = data.clone();
         drop(data);
-        println!("{:?}", &*data2);
+        assert_eq!(data2[0], String::from("Hello World"));
+        assert_eq!(data2[1], String::new());
+        assert_eq!(data2[2], String::from("This is a test"));
     }
 }

src/plane/error.rs

@@ -7,7 +7,7 @@
 // Media Patent License 1.0 was not distributed with this source code in the
 // PATENTS file, you can obtain it at www.aomedia.org/license/patent.
 
-use std::fmt;
+use core::fmt;
 
 /// An error representing why data couldn't be copied into a Plane.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -50,4 +50,4 @@ impl fmt::Display for CopyError {
     }
 }
 
-impl std::error::Error for CopyError {}
+impl core::error::Error for CopyError {}