I tried this code:
fn ieee_mod(a: f32, b: f32) -> f32 {
a - (a / b).round() * b
}
fn libc_mod(a: f32, b: f32) -> f32 {
a % b
}
fn main() {
let x = 1.5 * 3.14;
let y = 0.5 * 3.14;
assert_eq!(ieee_mod(x, y), libc_mod(x, y));
}I expected the assert to pass.
Instead, this happened:
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `0.0`,
right: `1.5699999`', bug.rs:14:5
Meta
This is most likely due to division being rounded, but mod not. This caused a bug in a sin table function I was writing.
This is standard libc behavior but it is still not correct and can cause bugs where none are expected.
rustc --version --verbose:
rustc 1.69.0 (84c898d65 2023-04-16)
binary: rustc
commit-hash: 84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc
commit-date: 2023-04-16
host: x86_64-unknown-linux-gnu
release: 1.69.0
LLVM version: 15.0.7
Backtrace
stack backtrace:
0: rust_begin_unwind
at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
1: core::panicking::panic_fmt
at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
2: core::panicking::assert_failed_inner
3: core::panicking::assert_failed
4: bug::main
5: core::ops::function::FnOnce::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
I tried this code:
I expected the assert to pass.
Instead, this happened:
Meta
This is most likely due to division being rounded, but mod not. This caused a bug in a sin table function I was writing.
This is standard libc behavior but it is still not correct and can cause bugs where none are expected.
rustc --version --verbose:Backtrace