ISO 6093 Real Number Parsing and Printing in Rust

ISO 6093:1985 is a standard for representing real numbers textually. It defines three forms: NR1, NR2, and NR3. These are used in ASN.1 encodings: specifically, in encoding REAL values using the Basic Encoding Rules (BER), Canonical Encoding Rules (CER), or Distinguished Encoding Rules (DER) as defined in ITU-T Recommendation X.690, but they could be used elsewhere.

This library implements functions for parsing and printing all three forms. It is a no-std-compatible crate and has no dependencies.

Overview

All formats defined in ISO 6093:1985 support leading SPACE characters and, if the signed variants are used, a positive or negative sign. All formats support using either the PERIOD or COMMA characters as the decimal mark, if a decimal mark is used.

First Numeric Representation (NR1) is for representing integers only. This crate stores integers on an f64 just for consistency with the other variants.

Second Numeric Representation (NR2) is the explicit-point real number. The value is simply printed using decimal digits, a decimal mark, and then the fractional digits. This is also a good format to use when it is known that the number will never be so large or small that it cannot be easily printed.

Third Numeric Representation (NR3) is "scientific notation."

Usage

You can parse numerical values having a particular format via parse_nr1, parse_nr2 and parse_nr3.

assert_eq!(parse_nr1(s!(" 0004902")), Ok(4902.0));
assert_eq!(parse_nr1(s!("   +1234")), Ok(1234.0));
assert_eq!(parse_nr1(s!("    1234")), Ok(1234.0));
assert_eq!(parse_nr1(s!("  -56780")), Ok(-56780.0));
assert_eq!(parse_nr2(s!("  1237,0")), Ok(1237.0));
assert_eq!(parse_nr2(s!("+0.00001")), Ok(0.00001));
assert_eq!(parse_nr2(s!("-5,67800")), Ok(-5.67800));
assert_eq!(parse_nr3(s!("+5.6e+03")), Ok(5600.0));
assert_eq!(parse_nr3(s!("+0,3E-04")), Ok(0.00003));
assert_eq!(parse_nr3(s!(" 0,3e-04")), Ok(0.00003));
assert_eq!(parse_nr3(s!("-2,8E+00")), Ok(-2.8));

Or, if which representation (NR1, NR2, or NR3) is unknown, you can try to parse any one of them using parse_iso6093:

assert_eq!(parse_iso6093(s!("0001234")), Ok(ISO6093RealNumber::NR1(1234.0)));
assert_eq!(parse_iso6093(s!("-05,6780")), Ok(ISO6093RealNumber::NR2(-5.6780)));
assert_eq!(parse_iso6093(s!("+0,3E-04")), Ok(ISO6093RealNumber::NR3(0.00003)));

You can also print values as such:

assert_eq!(ISO6093RealNumber::NR1(-123.0).to_string().as_str(), "-123");
assert_eq!(ISO6093RealNumber::NR2(0.00123).to_string().as_str(), "0.00123");
assert_eq!(ISO6093RealNumber::NR3(0.00123).to_string().as_str(), "1.23e-3");

ISO6093RealNumber implements Display and Debug, which can be used to print it as well.

No Alloc Usage

This library is no-std by default, but it is not zero-allocation by default. You can make it zero-allocation by turning off the default alloc feature flag, but this causes the API to change in the following manner: the functions parse_nr2, parse_nr3, and parse_iso6093 all change to take a &mut str instead of a &str. The reason for this is that, to parse the numbers, the string has to be "normalized" to change commas into periods. With no way to allocate a new string, the only other option is to modify the original. These implementations do NOT change it back.