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Challenges Reverse the bits in a Byte

ARM Thumb machine code, 6 bytes 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0 4: 4770 bx lr // return if bytes have to be octets (8-bit): ARM Thumb machine code...

posted 1y ago by lovebuny‭  ·  edited 1y ago by lovebuny‭

Answer
#3: Post edited by user avatar lovebuny‭ · 2023-09-08T23:52:22Z (about 1 year ago)
less whitespace
  • # ARM Thumb machine code, 6 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 4770 bx lr // return
  • ```
  • if bytes have to be octets (8-bit):
  • # ARM Thumb machine code, 8 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 0e00 lsrs r0, r0, #24 // shift it right by 24 bits
  • 6: 4770 bx lr // return
  • ```
  • # ARM Thumb machine code, 6 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 4770 bx lr // return
  • ```
  • if bytes have to be octets (8-bit):
  • # ARM Thumb machine code, 8 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 0e00 lsrs r0, r0, #24 // shift it right by 24 bits
  • 6: 4770 bx lr // return
  • ```
#2: Post edited by user avatar lovebuny‭ · 2023-09-08T23:16:06Z (about 1 year ago)
32-bit byte?
  • # ARM Thumb machine code, 8 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 0e00 lsrs r0, r0, #24 // shift it right by 24 bits
  • 6: 4770 bx lr // return
  • ```
  • # ARM Thumb machine code, 6 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 4770 bx lr // return
  • ```
  • if bytes have to be octets (8-bit):
  • # ARM Thumb machine code, 8 bytes
  • ```asm
  • 0: fa90 f0a0 rbit r0, r0 // reverse bits in 32-bit register 0
  • 4: 0e00 lsrs r0, r0, #24 // shift it right by 24 bits
  • 6: 4770 bx lr // return
  • ```
#1: Initial revision by user avatar lovebuny‭ · 2023-09-08T14:43:27Z (about 1 year ago)
# ARM Thumb machine code, 8 bytes

```asm
0: fa90 f0a0  rbit  r0, r0      // reverse bits in 32-bit register 0
4: 0e00       lsrs  r0, r0, #24 // shift it right by 24 bits
6: 4770       bx    lr          // return
```