Function parse_u64

cranelift/codegen/src/ir/immediates.rs:254–310

Parse a 64-bit unsigned number.

(s: &str)

/// Parse a 64-bit unsigned number.
fn parse_u64(s: &str) -> Result<u64, &'static str> {
    let mut value: u64 = 0;
    let mut digits = 0;

    if s.starts_with("-0x") {
        return Err("Invalid character in hexadecimal number");
    } else if let Some(num) = s.strip_prefix("0x") {
        // Hexadecimal.
        for ch in num.chars() {
            match ch.to_digit(16) {
                Some(digit) => {
                    digits += 1;
                    if digits > 16 {
                        return Err("Too many hexadecimal digits");
                    }
                    // This can't overflow given the digit limit.
                    value = (value << 4) | u64::from(digit);
                }
                None => {
                    // Allow embedded underscores, but fail on anything else.
                    if ch != '_' {
                        return Err("Invalid character in hexadecimal number");
                    }
                }
            }
        }
    } else {
        // Decimal number, possibly negative.
        for ch in s.chars() {
            match ch.to_digit(10) {
                Some(digit) => {
                    digits += 1;
                    match value.checked_mul(10) {
                        None => return Err("Too large decimal number"),
                        Some(v) => value = v,
                    }
                    match value.checked_add(u64::from(digit)) {
                        None => return Err("Too large decimal number"),
                        Some(v) => value = v,
                    }
                }
                None => {
                    // Allow embedded underscores, but fail on anything else.
                    if ch != '_' {
                        return Err("Invalid character in decimal number");
                    }
                }
            }
        }
    }

    if digits == 0 {
        return Err("No digits in number");
    }

    Ok(value)
}