How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?

I want to convert a u16 to two separate u8s. I tried to use some bit masks:

use std::convert::From;

fn main() 
 let n1: u8 = 0x41;
 let n2: u16 = 0x4157;

 println!("Number:", char::from(n1));

 let b1: u8 = n2 & 0xFF;
 let b2: u8 = n2 >> 8;

 println!("b1: ", b1);
 println!("b2: ", b2);

error[E0308]: mismatched types
 --> src/main.rs:9:18
 |
9 | let b1: u8 = n2 & 0xFF;
 | ^^^^^^^^^ expected u8, found u16

error[E0308]: mismatched types
 --> src/main.rs:10:18
 |
10 | let b2: u8 = n2 >> 8;
 | ^^^^^^^ expected u8, found u16

This question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

Reference

– jhpratt
Nov 15 '18 at 7:15

Possible duplicate of How to idiomatically convert between u32 and usize?

– E_net4
Nov 15 '18 at 9:52

@E_net4 not really I'm afraid

– hellow
Nov 15 '18 at 11:07

@hellow Quoting from the accepted answer: "The as operator works for all number types [...] Rust forces you to cast integers to make sure you're aware of signedness or overflows." Therefore, it pretty much answers why the compiler raises a mismatched types error.

– E_net4
Nov 15 '18 at 11:14

@E_net4 I would argue otherwise because the actual question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

– the_endian
Nov 15 '18 at 16:50

add a comment |

I want to convert a u16 to two separate u8s. I tried to use some bit masks:

use std::convert::From;

fn main() 
 let n1: u8 = 0x41;
 let n2: u16 = 0x4157;

 println!("Number:", char::from(n1));

 let b1: u8 = n2 & 0xFF;
 let b2: u8 = n2 >> 8;

 println!("b1: ", b1);
 println!("b2: ", b2);

error[E0308]: mismatched types
 --> src/main.rs:9:18
 |
9 | let b1: u8 = n2 & 0xFF;
 | ^^^^^^^^^ expected u8, found u16

error[E0308]: mismatched types
 --> src/main.rs:10:18
 |
10 | let b2: u8 = n2 >> 8;
 | ^^^^^^^ expected u8, found u16

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

Reference

– jhpratt
Nov 15 '18 at 7:15

Possible duplicate of How to idiomatically convert between u32 and usize?

– E_net4
Nov 15 '18 at 9:52

@E_net4 not really I'm afraid

– hellow
Nov 15 '18 at 11:07

@hellow Quoting from the accepted answer: "The as operator works for all number types [...] Rust forces you to cast integers to make sure you're aware of signedness or overflows." Therefore, it pretty much answers why the compiler raises a mismatched types error.

– E_net4
Nov 15 '18 at 11:14

@E_net4 I would argue otherwise because the actual question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

– the_endian
Nov 15 '18 at 16:50

add a comment |

I want to convert a u16 to two separate u8s. I tried to use some bit masks:

use std::convert::From;

fn main() 
 let n1: u8 = 0x41;
 let n2: u16 = 0x4157;

 println!("Number:", char::from(n1));

 let b1: u8 = n2 & 0xFF;
 let b2: u8 = n2 >> 8;

 println!("b1: ", b1);
 println!("b2: ", b2);

error[E0308]: mismatched types
 --> src/main.rs:9:18
 |
9 | let b1: u8 = n2 & 0xFF;
 | ^^^^^^^^^ expected u8, found u16

error[E0308]: mismatched types
 --> src/main.rs:10:18
 |
10 | let b2: u8 = n2 >> 8;
 | ^^^^^^^ expected u8, found u16

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

I want to convert a u16 to two separate u8s. I tried to use some bit masks:

use std::convert::From;

fn main() 
 let n1: u8 = 0x41;
 let n2: u16 = 0x4157;

 println!("Number:", char::from(n1));

 let b1: u8 = n2 & 0xFF;
 let b2: u8 = n2 >> 8;

 println!("b1: ", b1);
 println!("b2: ", b2);

error[E0308]: mismatched types
 --> src/main.rs:9:18
 |
9 | let b1: u8 = n2 & 0xFF;
 | ^^^^^^^^^ expected u8, found u16

error[E0308]: mismatched types
 --> src/main.rs:10:18
 |
10 | let b2: u8 = n2 >> 8;
 | ^^^^^^^ expected u8, found u16

rust bit-manipulation

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

edited Nov 15 '18 at 17:03

asked Nov 15 '18 at 6:59

the_endian

567622

asked Nov 15 '18 at 6:59

the_endian

567622

asked Nov 15 '18 at 6:59

the_endian

567622

Reference

– jhpratt
Nov 15 '18 at 7:15

Possible duplicate of How to idiomatically convert between u32 and usize?

– E_net4
Nov 15 '18 at 9:52

@E_net4 not really I'm afraid

– hellow
Nov 15 '18 at 11:07

@hellow Quoting from the accepted answer: "The as operator works for all number types [...] Rust forces you to cast integers to make sure you're aware of signedness or overflows." Therefore, it pretty much answers why the compiler raises a mismatched types error.

– E_net4
Nov 15 '18 at 11:14

@E_net4 I would argue otherwise because the actual question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

– the_endian
Nov 15 '18 at 16:50

add a comment |

Reference

– jhpratt
Nov 15 '18 at 7:15

Possible duplicate of How to idiomatically convert between u32 and usize?

– E_net4
Nov 15 '18 at 9:52

@E_net4 not really I'm afraid

– hellow
Nov 15 '18 at 11:07

@hellow Quoting from the accepted answer: "The as operator works for all number types [...] Rust forces you to cast integers to make sure you're aware of signedness or overflows." Therefore, it pretty much answers why the compiler raises a mismatched types error.

– E_net4
Nov 15 '18 at 11:14

@E_net4 I would argue otherwise because the actual question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

– the_endian
Nov 15 '18 at 16:50

Reference

– jhpratt
Nov 15 '18 at 7:15

Possible duplicate of How to idiomatically convert between u32 and usize?

– E_net4
Nov 15 '18 at 9:52

@E_net4 not really I'm afraid

– hellow
Nov 15 '18 at 11:07

@hellow Quoting from the accepted answer: "The as operator works for all number types [...] Rust forces you to cast integers to make sure you're aware of signedness or overflows." Therefore, it pretty much answers why the compiler raises a mismatched types error.

– E_net4
Nov 15 '18 at 11:14

@E_net4 I would argue otherwise because the actual question is not why does the compiler raise a mismatched type error?, rather, it is How can I convert the lower/upper 8 bits of a u16 to a u8 in Rust?. Potentially, there are other ways to do this and this question does not constrain the answer to the as keyword.

– the_endian
Nov 15 '18 at 16:50

add a comment |

2 Answers
2

active

oldest

votes

You can use the as keyword to convert a u16 to u8 in a safe way.

fn convert_u16_to_two_u8s_be(integer: u16) -> [u8; 2] 
 [(integer >> 8) as u8, integer as u8]

If you need more types or different endianness use the byteorder crate.

extern crate byteorder;

use byteorder::WriteBytesExt, BigEndian;

fn convert_u16_to_two_u8s_be(integer: u16) -> Vec<u8> 
 let mut res = vec!;
 res.write_u16::<BigEndian>(integer).unwrap();
 res

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

add a comment |

You can cast between integer types with as.

let b1 = n2 as u8;
let b2 = (n2 >> 8) as u8;

Note that the masking is unnecessary, because the cast will truncate the upper bits.

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

add a comment |

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

You can use the as keyword to convert a u16 to u8 in a safe way.

fn convert_u16_to_two_u8s_be(integer: u16) -> [u8; 2] 
 [(integer >> 8) as u8, integer as u8]

If you need more types or different endianness use the byteorder crate.

extern crate byteorder;

use byteorder::WriteBytesExt, BigEndian;

fn convert_u16_to_two_u8s_be(integer: u16) -> Vec<u8> 
 let mut res = vec!;
 res.write_u16::<BigEndian>(integer).unwrap();
 res

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

add a comment |

You can use the as keyword to convert a u16 to u8 in a safe way.

fn convert_u16_to_two_u8s_be(integer: u16) -> [u8; 2] 
 [(integer >> 8) as u8, integer as u8]

If you need more types or different endianness use the byteorder crate.

extern crate byteorder;

use byteorder::WriteBytesExt, BigEndian;

fn convert_u16_to_two_u8s_be(integer: u16) -> Vec<u8> 
 let mut res = vec!;
 res.write_u16::<BigEndian>(integer).unwrap();
 res

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

add a comment |

You can use the as keyword to convert a u16 to u8 in a safe way.

fn convert_u16_to_two_u8s_be(integer: u16) -> [u8; 2] 
 [(integer >> 8) as u8, integer as u8]

If you need more types or different endianness use the byteorder crate.

extern crate byteorder;

use byteorder::WriteBytesExt, BigEndian;

fn convert_u16_to_two_u8s_be(integer: u16) -> Vec<u8> 
 let mut res = vec!;
 res.write_u16::<BigEndian>(integer).unwrap();
 res

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

You can use the as keyword to convert a u16 to u8 in a safe way.

fn convert_u16_to_two_u8s_be(integer: u16) -> [u8; 2] 
 [(integer >> 8) as u8, integer as u8]

If you need more types or different endianness use the byteorder crate.

extern crate byteorder;

use byteorder::WriteBytesExt, BigEndian;

fn convert_u16_to_two_u8s_be(integer: u16) -> Vec<u8> 
 let mut res = vec!;
 res.write_u16::<BigEndian>(integer).unwrap();
 res

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

edited Nov 15 '18 at 15:59

Shepmaster

157k14316457

answered Nov 15 '18 at 7:31

hellow

5,34242242

answered Nov 15 '18 at 7:31

hellow

5,34242242

answered Nov 15 '18 at 7:31

hellow

5,34242242

add a comment |

You can cast between integer types with as.

let b1 = n2 as u8;
let b2 = (n2 >> 8) as u8;

Note that the masking is unnecessary, because the cast will truncate the upper bits.

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

add a comment |

You can cast between integer types with as.

let b1 = n2 as u8;
let b2 = (n2 >> 8) as u8;

Note that the masking is unnecessary, because the cast will truncate the upper bits.

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

add a comment |

You can cast between integer types with as.

let b1 = n2 as u8;
let b2 = (n2 >> 8) as u8;

Note that the masking is unnecessary, because the cast will truncate the upper bits.

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

You can cast between integer types with as.

let b1 = n2 as u8;
let b2 = (n2 >> 8) as u8;

Note that the masking is unnecessary, because the cast will truncate the upper bits.

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

answered Nov 15 '18 at 7:31

Benjamin Lindley

86.3k4138230

add a comment |

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