Rust for Python Developers - Unsigned, Signed Integers and Casting

Shin_O

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01 Introduction

02 Unsigned Integer Types

03 Signed Integer Types

04 Sign-and-Magnitude

05 Ones’ Complement

06 Two’s Complement

07 4-bit Signed Binary Number Comparison

08 Rust signed two’s complement integer types

09 Casting in Rust

10 Casting to an Unsigned Type

11 Casting to a Signed Type

12 Bitwise Negation

13 Conclusion

Previous: Casting to an Unsigned Type Next: Bitwise Negation

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Casting to a Signed Type

Method 1

This is the same as above but you need to be aware that the min/max number of the data type.

i8's min and max numbers are -128 and 127. So the number needs to be between them.

Casting 128 to i8 :

128-256=-128

Casting 1000 to i8:

1000 - 256 = 744
1000 - 256 - 256 = 488
1000 - 256 - 256 - 256 = 232
1000 - 256 - 256 - 256 - 256 = -24

#[allow(overflowing_literals)]
fn main() {
    println!("128 as a i8 is : {}", 128 as i8);
    println!("1000 as a i8 is : {}", 1000 as i8);
    println!("232 as a i8 is : {}", 232 as i8);
    println!("257 as a i8 is : {}", 257 as i8);
    println!("130 as a i8 is : {}", 130 as i8);
    println!("514 as a i8 is : {}", 514 as i8);
}
 

Method 2

1000₁₀ in decimal is 11 1110 1000₂ in binary. The MSB within 8-bit is 1, so it is a negative number. Then use 2’s complement. The complement is 00010111₂ and we add 1₂ becomes 00011000₂. Finally, it is -24₁₀.

4-bit word-4