Function parse_int_with_radix 

pub fn parse_int_with_radix(
    bytes: &[u8],
    radix: u32,
    allow_sep: bool,
) -> Option<f64>

Takes a non-empty string (without the leading “0x” if hex) and parses it as radix radix. allow_sep: when true, allow ‘_’ as a separator and ignore it when parsing. Returns the f64 that results on success, or None on error. Port of parseIntWithRadix (Conversions.h:204), including the >2^53 power-of-two bit-by-bit rounding path (lines 222–328).