rust/library/core/tests/num/dec2flt/rawfp.rs

use core::num::dec2flt::rawfp::RawFloat;
use core::num::dec2flt::rawfp::{fp_to_float, next_float, prev_float, round_normal};
use core::num::diy_float::Fp;

fn integer_decode(f: f64) -> (u64, i16, i8) {
    RawFloat::integer_decode(f)
}

#[test]
fn fp_to_float_half_to_even() {
    fn is_normalized(sig: u64) -> bool {
        // intentionally written without {min,max}_sig() as a sanity check
        sig >> 52 == 1 && sig >> 53 == 0
    }

    fn conv(sig: u64) -> u64 {
        // The significands are perfectly in range, so the exponent should not matter
        let (m1, e1, _) = integer_decode(fp_to_float::<f64>(Fp { f: sig, e: 0 }));
        assert_eq!(e1, 0 + 64 - 53);
        let (m2, e2, _) = integer_decode(fp_to_float::<f64>(Fp { f: sig, e: 55 }));
        assert_eq!(e2, 55 + 64 - 53);
        assert_eq!(m2, m1);
        let (m3, e3, _) = integer_decode(fp_to_float::<f64>(Fp { f: sig, e: -78 }));
        assert_eq!(e3, -78 + 64 - 53);
        assert_eq!(m3, m2);
        m3
    }

    let odd = 0x1F_EDCB_A012_345F;
    let even = odd - 1;
    assert!(is_normalized(odd));
    assert!(is_normalized(even));
    assert_eq!(conv(odd << 11), odd);
    assert_eq!(conv(even << 11), even);
    assert_eq!(conv(odd << 11 | 1 << 10), odd + 1);
    assert_eq!(conv(even << 11 | 1 << 10), even);
    assert_eq!(conv(even << 11 | 1 << 10 | 1), even + 1);
    assert_eq!(conv(odd << 11 | 1 << 9), odd);
    assert_eq!(conv(even << 11 | 1 << 9), even);
    assert_eq!(conv(odd << 11 | 0x7FF), odd + 1);
    assert_eq!(conv(even << 11 | 0x7FF), even + 1);
    assert_eq!(conv(odd << 11 | 0x3FF), odd);
    assert_eq!(conv(even << 11 | 0x3FF), even);
}

#[test]
fn integers_to_f64() {
    assert_eq!(fp_to_float::<f64>(Fp { f: 1, e: 0 }), 1.0);
    assert_eq!(fp_to_float::<f64>(Fp { f: 42, e: 7 }), (42 << 7) as f64);
    assert_eq!(fp_to_float::<f64>(Fp { f: 1 << 20, e: 30 }), (1u64 << 50) as f64);
    assert_eq!(fp_to_float::<f64>(Fp { f: 4, e: -3 }), 0.5);
}

const SOME_FLOATS: [f64; 9] = [
    0.1f64,
    33.568,
    42.1e-5,
    777.0e9,
    1.1111,
    0.347997,
    9843579834.35892,
    12456.0e-150,
    54389573.0e-150,
];

#[test]
fn human_f64_roundtrip() {
    for &x in &SOME_FLOATS {
        let (f, e, _) = integer_decode(x);
        let fp = Fp { f: f, e: e };
        assert_eq!(fp_to_float::<f64>(fp), x);
    }
}

#[test]
fn rounding_overflow() {
    let x = Fp { f: 0xFF_FF_FF_FF_FF_FF_FF_00u64, e: 42 };
    let rounded = round_normal::<f64>(x);
    let adjusted_k = x.e + 64 - 53;
    assert_eq!(rounded.sig, 1 << 52);
    assert_eq!(rounded.k, adjusted_k + 1);
}

#[test]
fn prev_float_monotonic() {
    let mut x = 1.0;
    for _ in 0..100 {
        let x1 = prev_float(x);
        assert!(x1 < x);
        assert!(x - x1 < 1e-15);
        x = x1;
    }
}

const MIN_SUBNORMAL: f64 = 5e-324;

#[test]
fn next_float_zero() {
    let tiny = next_float(0.0);
    assert_eq!(tiny, MIN_SUBNORMAL);
    assert!(tiny != 0.0);
}

#[test]
fn next_float_subnormal() {
    let second = next_float(MIN_SUBNORMAL);
    // For subnormals, MIN_SUBNORMAL is the ULP
    assert!(second != MIN_SUBNORMAL);
    assert!(second > 0.0);
    assert_eq!(second - MIN_SUBNORMAL, MIN_SUBNORMAL);
}

#[test]
fn next_float_inf() {
    assert_eq!(next_float(f64::MAX), f64::INFINITY);
    assert_eq!(next_float(f64::INFINITY), f64::INFINITY);
}

#[test]
fn next_prev_identity() {
    for &x in &SOME_FLOATS {
        assert_eq!(prev_float(next_float(x)), x);
        assert_eq!(prev_float(prev_float(next_float(next_float(x)))), x);
        assert_eq!(next_float(prev_float(x)), x);
        assert_eq!(next_float(next_float(prev_float(prev_float(x)))), x);
    }
}

#[test]
fn next_float_monotonic() {
    let mut x = 0.49999999999999;
    assert!(x < 0.5);
    for _ in 0..200 {
        let x1 = next_float(x);
        assert!(x1 > x);
        assert!(x1 - x < 1e-15, "next_float_monotonic: delta = {:?}", x1 - x);
        x = x1;
    }
    assert!(x > 0.5);
}

#[test]
fn test_f32_integer_decode() {
    assert_eq!(3.14159265359f32.integer_decode(), (13176795, -22, 1));
    assert_eq!((-8573.5918555f32).integer_decode(), (8779358, -10, -1));
    assert_eq!(2f32.powf(100.0).integer_decode(), (8388608, 77, 1));
    assert_eq!(0f32.integer_decode(), (0, -150, 1));
    assert_eq!((-0f32).integer_decode(), (0, -150, -1));
    assert_eq!(f32::INFINITY.integer_decode(), (8388608, 105, 1));
    assert_eq!(f32::NEG_INFINITY.integer_decode(), (8388608, 105, -1));

    // Ignore the "sign" (quiet / signalling flag) of NAN.
    // It can vary between runtime operations and LLVM folding.
    let (nan_m, nan_e, _nan_s) = f32::NAN.integer_decode();
    assert_eq!((nan_m, nan_e), (12582912, 105));
}

#[test]
fn test_f64_integer_decode() {
    assert_eq!(3.14159265359f64.integer_decode(), (7074237752028906, -51, 1));
    assert_eq!((-8573.5918555f64).integer_decode(), (4713381968463931, -39, -1));
    assert_eq!(2f64.powf(100.0).integer_decode(), (4503599627370496, 48, 1));
    assert_eq!(0f64.integer_decode(), (0, -1075, 1));
    assert_eq!((-0f64).integer_decode(), (0, -1075, -1));
    assert_eq!(f64::INFINITY.integer_decode(), (4503599627370496, 972, 1));
    assert_eq!(f64::NEG_INFINITY.integer_decode(), (4503599627370496, 972, -1));

    // Ignore the "sign" (quiet / signalling flag) of NAN.
    // It can vary between runtime operations and LLVM folding.
    let (nan_m, nan_e, _nan_s) = f64::NAN.integer_decode();
    assert_eq!((nan_m, nan_e), (6755399441055744, 972));
}