module math

// floor returns the greatest integer value less than or equal to x.
//
// special cases are:
// floor(±0) = ±0
// floor(±inf) = ±inf
// floor(nan) = nan
pub fn floor(x f64) f64 {
    if x == 0 || is_nan(x) || is_inf(x, 0) {
        return x
    }
    if x < 0 {
        mut d, fract := modf(-x)
        if fract != 0.0 {
            d = d + 1
        }
        return -d
    }
    d, _ := modf(x)
    return d
}

// ceil returns the least integer value greater than or equal to x.
//
// special cases are:
// ceil(±0) = ±0
// ceil(±inf) = ±inf
// ceil(nan) = nan
pub fn ceil(x f64) f64 {
    return -floor(-x)
}

// trunc returns the integer value of x.
//
// special cases are:
// trunc(±0) = ±0
// trunc(±inf) = ±inf
// trunc(nan) = nan
pub fn trunc(x f64) f64 {
    if x == 0 || is_nan(x) || is_inf(x, 0) {
        return x
    }
    d, _ := modf(x)
    return d
}

// round returns the nearest integer, rounding half away from zero.
//
// special cases are:
// round(±0) = ±0
// round(±inf) = ±inf
// round(nan) = nan
pub fn round(x f64) f64 {
    if x == 0 || is_nan(x) || is_inf(x, 0) {
        return x
    }
    // Largest integer <= x
    mut y := floor(x) // Fractional part
    mut r := x - y // Round up to nearest.
    if r > 0.5 {
        unsafe {
            goto rndup
        }
    }
    // Round to even
    if r == 0.5 {
        r = y - 2.0 * floor(0.5 * y)
        if r == 1.0 {
            rndup:
            y += 1.0
        }
    }
    // Else round down.
    return y
}

// Returns the rounded float, with sig_digits of precision.
// i.e `assert round_sig(4.3239437319748394,6) == 4.323944`
pub fn round_sig(x f64, sig_digits int) f64 {
    mut ret_str := '${x}'

    match sig_digits {
        0 { ret_str = '${x:0.0f}' }
        1 { ret_str = '${x:0.1f}' }
        2 { ret_str = '${x:0.2f}' }
        3 { ret_str = '${x:0.3f}' }
        4 { ret_str = '${x:0.4f}' }
        5 { ret_str = '${x:0.5f}' }
        6 { ret_str = '${x:0.6f}' }
        7 { ret_str = '${x:0.7f}' }
        8 { ret_str = '${x:0.8f}' }
        9 { ret_str = '${x:0.9f}' }
        10 { ret_str = '${x:0.10f}' }
        11 { ret_str = '${x:0.11f}' }
        12 { ret_str = '${x:0.12f}' }
        13 { ret_str = '${x:0.13f}' }
        14 { ret_str = '${x:0.14f}' }
        15 { ret_str = '${x:0.15f}' }
        16 { ret_str = '${x:0.16f}' }
        else { ret_str = '${x}' }
    }

    return ret_str.f64()
}

// round_to_even returns the nearest integer, rounding ties to even.
//
// special cases are:
// round_to_even(±0) = ±0
// round_to_even(±inf) = ±inf
// round_to_even(nan) = nan
pub fn round_to_even(x f64) f64 {
    mut bits := f64_bits(x)
    mut e_ := (bits >> shift) & mask
    if e_ >= bias {
        // round abs(x) >= 1.
        // - Large numbers without fractional components, infinity, and nan are unchanged.
        // - Add 0.499.. or 0.5 before truncating depending on whether the truncated
        // number is even or odd (respectively).
        half_minus_ulp := u64(u64(1) << (shift - 1)) - 1
        e_ -= u64(bias)
        bits += (half_minus_ulp + (bits >> (shift - e_)) & 1) >> e_
        bits &= frac_mask >> e_
        bits ^= frac_mask >> e_
    } else if e_ == bias - 1 && bits & frac_mask != 0 {
        // round 0.5 < abs(x) < 1.
        bits = bits & sign_mask | uvone // +-1
    } else {
        // round abs(x) <= 0.5 including denormals.
        bits &= sign_mask // +-0
    }
    return f64_from_bits(bits)
}