Constant std::f32::MANTISSA_DIGITS
pub const MANTISSA_DIGITS: u32 = f32::MANTISSA_DIGITS; // 0x0000_0018u32
???? Deprecating in a future Rust version: 
replaced by the MANTISSA_DIGITS associated constant on f32
Number of significant digits in base 2. Use f32::MANTISSA_DIGITS instead.
Examples
// deprecated way let d = std::f32::MANTISSA_DIGITS; // intended way let d = f32::MANTISSA_DIGITS;
    © 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
    https://doc.rust-lang.org/std/f32/constant.MANTISSA_DIGITS.html