Crate zerodds_float128 

Crate zerodds-float128. Safety classification: SAFE.

IEEE 754 binary128, in software.

CDR gives long double sixteen bytes and CORBA 3.3 part 2 §9.3.1.3 says what is in them: one sign bit, a fifteen-bit exponent biased by 16383, and a 112-bit stored fraction. That is binary128, and DDS-XTypes 1.3 Table 31 names it — “IEEE standard for normalized quadruple-precision floating-point numbers”, encoded size sixteen, alignment eight.

Rust has no stable f128, and every serialiser in this project used to answer that by writing a double and eight zero bytes: the right length and the wrong value, in silence. This crate is the answer instead. A wire runtime does not need to compute with a quadruple — it needs to carry one exactly, compare it, and read and write it as text. Those are bit manipulation and long division, not research.

What is here

• Float128 — the value, one u128 of IEEE 754 binary128 pattern.
• Lossless sixteen-byte round trip in both byte orders.
• Exact conversion from f32, f64 and the integer types, and back with the inexact cases reported rather than rounded in silence.
• IEEE comparison, and Float128::total_cmp for the places that need a total order — a key holder, a sorted expectation.
• Decimal parsing and formatting that round-trips, so a JSON value file can carry one.
• x87 — the 80-bit extended format, because two of the four DDS vendors put that on the wire on x86 and a type that knows only the conformant form cannot read what the field actually sends.

What is not here

Arithmetic. Add, Sub, Mul, Div and sqrt are not implemented; docs/float128-column.md §6 says what they would take. Nothing in the wire path needs them, and a half-correct Add is worse than none.

Spec

• CORBA 3.3 part 2 §9.3.1.1 (alignment) and §9.3.1.3 with Figure 9.2 (the bit layout, and the whole-sixteen-byte order reversal).
• DDS-XTypes 1.3 §7.4.1.1.1 Table 31 (size sixteen, alignment eight) and §7.4.3.2.2 MAXALIGN (four under XCDR2).
• IEEE 754-2008 clause 3.6 for binary128 itself.

Layer position

Layer 0. Depends on nothing.

Modules

x87

The 80-bit extended format, because the field sends it.

Structs

Float128

An IEEE 754-2008 binary128 value.

Inexact

A conversion that could not be exact.

Enums

Class

What a value is, in the sense of IEEE 754-2008 clause 5.7.2.

ParseFloat128Error

Why a decimal string is not a binary128 value.