From 4c671a425015d1e7bc191d45f143147579f5809a Mon Sep 17 00:00:00 2001
From: Federico Bruzzone <federico.bruzzone.i@gmail.com>
Date: Thu, 15 Sep 2022 16:14:54 +0200
Subject: [PATCH] API: Add `clear` function to `bitwise`

These function complete the bitwise file.
- The first one allow us to clean (set to 0) all bits from `msg` to `idx`;
- The second one allow us to clean (set to 0) all bits from `idx` to `0`

Signed-off-by: Federico Bruzzone <federico.bruzzone.i@gmail.com>
---
 src/bitwise.rs | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/src/bitwise.rs b/src/bitwise.rs
index 2bafcb20..89dba34e 100644
--- a/src/bitwise.rs
+++ b/src/bitwise.rs
@@ -8,6 +8,8 @@ pub trait Bits {
     fn toggle_bit(&mut self, bit_idx: u8);
     fn set_bit(&mut self, bit_idx: u8, value: bool);
     fn get_bit(self, bit_idx: u8) -> bool;
+    fn clear_bits_msb_to_idx(&mut self, bit_idx: u8); // msb: most significant bit
+    fn clear_bits_idx_to_0(&mut self, bit_idx: u8);
 }
 
 impl Bits for u32 {
@@ -57,6 +59,22 @@ impl Bits for u32 {
     fn get_bit(self, bit_idx: u8) -> bool {
         self.is_bit_on(bit_idx)
     }
+
+    /// To clear all bits from the `most significant bit` through `bit_idx` (inclusive)
+    fn clear_bits_msb_to_idx(&mut self, bit_idx: u8) {
+        debug_assert!(bit_idx < 32);
+
+        let mask = (1 << bit_idx) - 1;
+        *self &= mask;
+    }
+
+    /// To clear all bits from `bit_idx` through `0` (inclusive)
+    fn clear_bits_idx_to_0(&mut self, bit_idx: u8) {
+        debug_assert!(bit_idx < 32);
+
+        let mask = -1_i32 << (bit_idx + 1);
+        *self &= mask as u32;
+    }
 }
 
 #[cfg(test)]
@@ -64,6 +82,20 @@ mod tests {
     use super::*;
     use rand::Rng;
 
+    #[test]
+    fn test_clear_bits_msb_to_idx() {
+        let mut b = 0b11111111;
+        b.clear_bits_msb_to_idx(3);
+        println!("{}", b)
+    }
+
+    #[test]
+    fn test_clear_bits_idx_to_0() {
+        let mut b = 0b11111;
+        b.clear_bits_idx_to_0(3);
+        println!("{}", b)
+    }
+
     #[test]
     fn test_is_on() {
         let b = 0b110011101_u32;