magiclen-byte-unit/PR.md

Fix no_std panic in Byte::from_f64/from_f32 on non-finite input

Problem

Byte::from_f64 and Byte::from_f32 are documented to return None when the input is "too large" or not >= 0. In std builds a non-finite input such as f64::INFINITY correctly returns None, but in no_std builds it panics:

// with `--no-default-features --features byte`
byte_unit::Byte::from_f64(f64::INFINITY);
// thread panicked at src/common.rs:39:
// called `Option::unwrap()` on a `None` value

So the same call behaves differently across the two build configurations and breaks the documented contract in no_std.

Root cause

from_f64/from_f32 guard the input with if size >= 0.0, which rejects NaN (since NaN >= 0.0 is false) but lets +inf through. The value is then passed to ceil_f64/ceil_f32 in src/common.rs.

The std implementation uses v.ceil(), which returns inf; the subsequent inf as u128/as u64 cast saturates to the maximum, and the range check then returns None.

The no_std implementation instead does:

Decimal::from_f64(v).unwrap().ceil().to_f64().unwrap()

Decimal::from_f64 (and from_f32) returns None for non-finite values, so .unwrap() panics. The no_std helper therefore diverges from the std one.

Fix

Make the no_std ceil_f64/ceil_f32 fall back to the input value when it is not representable as a Decimal (i.e. non-finite), mirroring f64::ceil:

match Decimal::from_f64(v) {
    Some(d) => d.ceil().to_f64().unwrap_or(v),
    None => v,
}

With this, from_f64(f64::INFINITY) flows through the same saturating cast and range check as in std, returning None. Finite values are unaffected.

Test

Added from_non_finite_returns_none to tests/byte.rs, asserting that from_f64/from_f32 return None for both infinity and NaN. It passes under --all-features and under --no-default-features --features byte (the config that previously panicked).

Gate

• cargo test --all-features -> ok (exit 0)
• cargo test --no-default-features --features byte,bit -> ok (exit 0)
• cargo build --all-features -> ok (exit 0)
• cargo clippy --all-targets --all-features -- -D warnings -> ok (exit 0)
• cargo clippy --no-default-features --features byte,bit -- -D warnings -> ok (exit 0)

Counterfactual

Restoring Decimal::from_f64(v).unwrap()... makes the new test panic under the no_std config:

thread 'from_non_finite_returns_none' panicked at src/common.rs:39:26:
called `Option::unwrap()` on a `None` value

Flags for the account owner

cargo fmt --check reports differences, but this is pre-existing and unrelated to this change: rustfmt.toml enables nightly-only options (e.g. binop_separator, imports_granularity), so a stable rustfmt reformats many untouched files. On an unmodified checkout cargo fmt --check already reports the same differences. The two files changed here were edited by hand to match the surrounding style.