decimal-scaled 0.2.2

//! `D38::rescale` / `rescale_with` integration tests. Moved out of
//! `src/rescale.rs` so that file carries only macro invocations.
//!
//! Several tests below use the plain `rescale::<N>()` form, whose
//! rounding behaviour depends on the crate-default mode. Compile-gate
//! the whole file to the `HalfToEven` default so every test always
//! executes its assertions (no silent skip under a `rounding-*` build).

#![cfg(not(any(
    feature = "rounding-half-away-from-zero",
    feature = "rounding-half-toward-zero",
    feature = "rounding-trunc",
    feature = "rounding-floor",
    feature = "rounding-ceiling",
)))]

use decimal_scaled::{D38s2, D38s6, D38s12, RoundingMode};

// --- with_scale alias ----------------------------------------------

#[test]
fn with_scale_matches_rescale() {
    // Native tier.
    let a = D38s2::from_bits(150);
    assert_eq!(a.with_scale::<6>().to_bits(), a.rescale::<6>().to_bits());
    assert_eq!(a.with_scale::<2>().to_bits(), a.to_bits());

    // The builder-style name is the only difference; semantics are
    // bit-identical to rescale.
    let b = D38s12::from_bits(12_345_678_901_234);
    assert_eq!(b.with_scale::<6>().to_bits(), b.rescale::<6>().to_bits());
}

// --- scale-up direction --------------------------------------------

#[test]
fn rescale_up_appends_zeros() {
    let cents = D38s2::from_bits(150);
    let micros = cents.rescale::<6>();
    assert_eq!(micros.to_bits(), 1_500_000);
}

#[test]
fn rescale_up_negative() {
    let cents = D38s2::from_bits(-150);
    let micros = cents.rescale::<6>();
    assert_eq!(micros.to_bits(), -1_500_000);
}

#[test]
fn rescale_up_zero() {
    let z = D38s2::from_bits(0);
    let m = z.rescale::<12>();
    assert_eq!(m.to_bits(), 0);
}

#[test]
#[should_panic(expected = "scale-up overflow")]
fn rescale_up_overflow_panics() {
    let big = D38s12::from_bits(i128::MAX);
    // Going from scale 12 to scale 38 multiplies by 10^26, which
    // overflows for any non-tiny source.
    let _ = big.rescale::<38>();
}

// --- scale-down direction (default = HalfToEven) -------------------

#[test]
fn rescale_down_truncates_zero_remainder() {
    let micros = D38s6::from_bits(1_500_000);
    let cents = micros.rescale::<2>();
    assert_eq!(cents.to_bits(), 150);
}

#[test]
fn rescale_down_half_to_even_rounds_to_even() {
    use decimal_scaled::RoundingMode;
    // Pin the mode so this test verifies HalfToEven specifically,
    // regardless of which `rounding-*` feature happens to be set.
    // 1.235000 at cents: tie -> 1.24 (4 is even)
    let micros = D38s6::from_bits(1_235_000);
    assert_eq!(
        micros.rescale_with::<2>(RoundingMode::HalfToEven).to_bits(),
        124
    );

    // 1.225000 at cents: tie -> 1.22 (2 is even)
    let micros = D38s6::from_bits(1_225_000);
    assert_eq!(
        micros.rescale_with::<2>(RoundingMode::HalfToEven).to_bits(),
        122
    );
}

#[test]
fn rescale_down_non_half_goes_nearest() {
    // 1.234999 -> 1.23 (below half)
    let micros = D38s6::from_bits(1_234_999);
    assert_eq!(micros.rescale::<2>().to_bits(), 123);
    // 1.235001 -> 1.24 (above half)
    let micros = D38s6::from_bits(1_235_001);
    assert_eq!(micros.rescale::<2>().to_bits(), 124);
}

#[test]
fn rescale_down_negative_half_to_even() {
    // -1.235000 -> -1.24 (tie, 4 is even — sign symmetric)
    let micros = D38s6::from_bits(-1_235_000);
    assert_eq!(micros.rescale::<2>().to_bits(), -124);
}

// --- rescale_with mode coverage ------------------------------------

#[test]
fn rescale_with_each_mode_at_exact_half() {
    let micros = D38s6::from_bits(1_235_000); // 1.235000

    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfToEven).to_bits(), 124);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfAwayFromZero).to_bits(), 124);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfTowardZero).to_bits(), 123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Trunc).to_bits(), 123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Floor).to_bits(), 123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Ceiling).to_bits(), 124);
}

#[test]
fn rescale_with_each_mode_at_exact_half_negative() {
    let micros = D38s6::from_bits(-1_235_000); // -1.235000

    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfToEven).to_bits(), -124);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfAwayFromZero).to_bits(), -124);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::HalfTowardZero).to_bits(), -123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Trunc).to_bits(), -123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Floor).to_bits(), -124);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Ceiling).to_bits(), -123);
}

#[test]
fn rescale_with_trunc_vs_floor_diverge_on_negative() {
    // -1.234500 (below the half-tie boundary in magnitude)
    let micros = D38s6::from_bits(-1_234_500);
    // Trunc rounds toward zero -> -1.23 (the half-tie isn't here; remainder is below half on this one)
    // Wait: divisor = 10^4 = 10000, abs_rem = 4500 which is < half (5000). So no rounding occurs.
    // Both Trunc and Floor return quotient = -123.
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Trunc).to_bits(), -123);
    assert_eq!(micros.rescale_with::<2>(RoundingMode::Floor).to_bits(), -124);
}

// --- equal scale identity ------------------------------------------

#[test]
fn rescale_same_scale_is_bit_identity() {
    let v = D38s12::from_bits(123_456_789_012);
    let same: D38s12 = v.rescale::<12>();
    assert_eq!(same.to_bits(), 123_456_789_012);
}

#[test]
fn rescale_with_same_scale_is_bit_identity_for_every_mode() {
    let v = D38s12::from_bits(123_456_789_012);
    for m in [
        RoundingMode::HalfToEven,
        RoundingMode::HalfAwayFromZero,
        RoundingMode::HalfTowardZero,
        RoundingMode::Trunc,
        RoundingMode::Floor,
        RoundingMode::Ceiling,
    ] {
        assert_eq!(v.rescale_with::<12>(m).to_bits(), 123_456_789_012, "{m:?}");
    }
}

// --- const-fn usability --------------------------------------------

#[test]
fn rescale_works_in_const_context() {
    const SRC: D38s6 = D38s6::from_bits(1_235_000);
    const DST: D38s2 = SRC.rescale::<2>();
    assert_eq!(DST.to_bits(), 124);
}