From ca68649cbc91bc5d701e7b983ee9a080f9d495d1 Mon Sep 17 00:00:00 2001
From: rsahwe <rsahwe@gmx.net>
Date: Thu, 17 Apr 2025 20:52:59 +0200
Subject: [PATCH] Remove unnecessary alloc usage

---
 Cargo.toml        |  4 ++++
 README.md         |  2 ++
 src/bitmap/fmt.rs | 54 ++++++++++++++++++++++++++++++++++++++++++++++-
 src/lib.rs        |  1 +
 4 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index 2a8110b..6e7839c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,6 +22,10 @@ bench = false # ignoring libtest check, so criterion cmd options can be used.
 [dev-dependencies]
 criterion = { version = "0.4", features = ["html_reports"] }
 
+[features]
+default = ["alloc"]
+alloc = []
+
 [[example]]
 name = "bitmap-base"
 [[example]]
diff --git a/README.md b/README.md
index 6d58224..1e52eee 100644
--- a/README.md
+++ b/README.md
@@ -67,6 +67,8 @@
   the map is relatively small like 8 or 16 bits,
   you can put it on stack safely. If it is larger like 256 or
   1024 bits, you may want to put it on heap.
+
+  The alloc feature which is enabled by default is only used for formatting.
   
 ## Examples
 
diff --git a/src/bitmap/fmt.rs b/src/bitmap/fmt.rs
index 8bbf547..99731ad 100644
--- a/src/bitmap/fmt.rs
+++ b/src/bitmap/fmt.rs
@@ -1,9 +1,59 @@
 //! Implementations of formating methods for `Bitmap`, including [`Debug`].
 
+#[cfg(feature = "alloc")]
 use alloc::{string::{String, ToString}, format};
 
 use crate::bitmap::*;
 
+#[cfg(not(feature = "alloc"))]
+impl<const BYTES: usize> core::fmt::Display for Bitmap<BYTES> {
+    /// Formats a bitmap. Only shows the last 2 bytes if the bitmap is longer.
+    /// The bytes will be separated by space `' '`. 
+    /// 
+    /// The bits will be arranged from right to left. If the bitmap is longer than 
+    /// 2 bytes, a `"..."` will show on the left.
+    /// On the very left, a bracket tells the bit length of the map (in a form 
+    /// like `"[N bits]"`). A space `' '` will be between the bit contents and this
+    /// bracket.
+    /// 
+    /// # Examples
+    /// ```
+    /// use cbitmap::bitmap::*;
+    /// 
+    /// let mut map: Bitmap<3> = 0.into();
+    /// map.set(0);
+    /// map.set(8);
+    /// let str = &format!("{map}");
+    /// assert_eq!(str, "[24 bits] ...00000001 00000001");
+    /// ```
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "[{} bits] ", BYTES * 8)?;
+        let size = 2.min(BYTES);
+        if BYTES > size {
+            write!(f, "...")?;
+        }
+        for i in 0..size {
+            if i > 0 {
+                write!(f, " ")?;
+            }
+            write!(f, "{:08b}", self.__copy_u8(size - i - 1))?;
+        }
+        Ok(())
+    }
+}
+
+#[cfg(not(feature = "alloc"))]
+impl<const BYTES: usize> core::fmt::Debug for Bitmap<BYTES> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("Bitmap")
+            .field("#bytes", &BYTES)
+            .field("#bits", &(BYTES * 8))
+            .field("bits", &self.bits)
+            .finish()
+    }
+}
+
+#[cfg(feature = "alloc")]
 impl<const BYTES: usize> core::fmt::Display for Bitmap<BYTES> {
     /// Formats a bitmap. Only shows the last 2 bytes if the bitmap is longer.
     /// The bytes will be separated by space `' '`. 
@@ -41,6 +91,7 @@ impl<const BYTES: usize> core::fmt::Display for Bitmap<BYTES> {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl<const BYTES: usize> core::fmt::Debug for Bitmap<BYTES> {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         let mut contents = String::new();
@@ -63,6 +114,7 @@ impl<const BYTES: usize> core::fmt::Debug for Bitmap<BYTES> {
     }
 }
 
+#[cfg(feature = "alloc")]
 impl<const BYTES: usize> Bitmap<BYTES> {
     /// Format a range of bits into a [`Option<String>`].
     /// 
@@ -117,4 +169,4 @@ impl<const BYTES: usize> Bitmap<BYTES> {
 
         Some(contents)
     }
-}
\ No newline at end of file
+}
diff --git a/src/lib.rs b/src/lib.rs
index db84b8a..492a6a7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -166,6 +166,7 @@
 //! not `BitRef` due to a similar issue.
 #![no_std]
 
+#[cfg(feature = "alloc")]
 extern crate alloc;
 
 mod tools;