frexp

pub fn frexp(x: anytype) Frexp(@TypeOf(x)) {
    const T: type = @TypeOf(x);

    const bits: comptime_int = @typeInfo(T).float.bits;
    const Int: type = std.meta.Int(.unsigned, bits);

    const exp_bits: comptime_int = math.floatExponentBits(T);
    const mant_bits: comptime_int = math.floatMantissaBits(T);
    const frac_bits: comptime_int = math.floatFractionalBits(T);
    const exp_min: comptime_int = math.floatExponentMin(T);

    const ExpInt: type = std.meta.Int(.unsigned, exp_bits);
    const MantInt: type = std.meta.Int(.unsigned, mant_bits);
    const FracInt: type = std.meta.Int(.unsigned, frac_bits);

    const unreal_exponent: comptime_int = (1 << exp_bits) - 1;
    const bias: comptime_int = (1 << (exp_bits - 1)) - 2;
    const exp_mask: comptime_int = unreal_exponent << mant_bits;
    const zero_exponent: comptime_int = bias << mant_bits;
    const sign_mask: comptime_int = 1 << (bits - 1);
    const not_exp: comptime_int = ~@as(Int, exp_mask);
    const ones_place: comptime_int = mant_bits - frac_bits;
    const extra_denorm_shift: comptime_int = 1 - ones_place;

    var result: Frexp(T) = undefined;
    var v: Int = @bitCast(x);

    const m: MantInt = @truncate(v);
    const e: ExpInt = @truncate(v >> mant_bits);

    switch (e) {
        0 => {
            if (m != 0) {
                // subnormal
                const offset = @clz(m);
                const shift = offset + extra_denorm_shift;

                v &= sign_mask;
                v |= zero_exponent;
                v |= math.shl(MantInt, m, shift);

                result.exponent = exp_min - @as(i32, offset) + ones_place;
            } else {
                // +-0 = (+-0, 0)
                result.exponent = 0;
            }
        },
        unreal_exponent => {
            // +-nan -> {+-nan, undefined}
            result.exponent = undefined;

            // +-inf -> {+-inf, 0}
            if (@as(FracInt, @truncate(v)) == 0)
                result.exponent = 0;
        },
        else => {
            // normal
            v &= not_exp;
            v |= zero_exponent;
            result.exponent = @as(i32, e) - bias;
        },
    }

    result.significand = @bitCast(v);
    return result;
}