src/libcore/tests/num/flt2dec/estimator.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// FIXME https://github.com/kripken/emscripten/issues/4563
// NB we have to actually not compile this test to avoid
// an undefined symbol error
#![cfg(not(target_os = "emscripten"))]

use core::num::flt2dec::estimator::*;

#[test]
fn test_estimate_scaling_factor() {
    macro_rules! assert_almost_eq {
        ($actual:expr, $expected:expr) => ({
            let actual = $actual;
            let expected = $expected;
            println!("{} - {} = {} - {} = {}", stringify!($expected), stringify!($actual),
                     expected, actual, expected - actual);
            assert!(expected == actual || expected == actual + 1,
                    "expected {}, actual {}", expected, actual);
        })
    }

    assert_almost_eq!(estimate_scaling_factor(1, 0), 0);
    assert_almost_eq!(estimate_scaling_factor(2, 0), 1);
    assert_almost_eq!(estimate_scaling_factor(10, 0), 1);
    assert_almost_eq!(estimate_scaling_factor(11, 0), 2);
    assert_almost_eq!(estimate_scaling_factor(100, 0), 2);
    assert_almost_eq!(estimate_scaling_factor(101, 0), 3);
    assert_almost_eq!(estimate_scaling_factor(10000000000000000000, 0), 19);
    assert_almost_eq!(estimate_scaling_factor(10000000000000000001, 0), 20);

    // 1/2^20 = 0.00000095367...
    assert_almost_eq!(estimate_scaling_factor(1 * 1048576 / 1000000, -20), -6);
    assert_almost_eq!(estimate_scaling_factor(1 * 1048576 / 1000000 + 1, -20), -5);
    assert_almost_eq!(estimate_scaling_factor(10 * 1048576 / 1000000, -20), -5);
    assert_almost_eq!(estimate_scaling_factor(10 * 1048576 / 1000000 + 1, -20), -4);
    assert_almost_eq!(estimate_scaling_factor(100 * 1048576 / 1000000, -20), -4);
    assert_almost_eq!(estimate_scaling_factor(100 * 1048576 / 1000000 + 1, -20), -3);
    assert_almost_eq!(estimate_scaling_factor(1048575, -20), 0);
    assert_almost_eq!(estimate_scaling_factor(1048576, -20), 0);
    assert_almost_eq!(estimate_scaling_factor(1048577, -20), 1);
    assert_almost_eq!(estimate_scaling_factor(10485759999999999999, -20), 13);
    assert_almost_eq!(estimate_scaling_factor(10485760000000000000, -20), 13);
    assert_almost_eq!(estimate_scaling_factor(10485760000000000001, -20), 14);

    // extreme values:
    // 2^-1074 = 4.94065... * 10^-324
    // (2^53-1) * 2^971 = 1.79763... * 10^308
    assert_almost_eq!(estimate_scaling_factor(1, -1074), -323);
    assert_almost_eq!(estimate_scaling_factor(0x1fffffffffffff, 971), 309);

    for i in -1074..972 {
        let expected = super::ldexp_f64(1.0, i).log10().ceil();
        assert_almost_eq!(estimate_scaling_factor(1, i as i16), expected as i16);
    }
}