Function wrap [src]

Odd sawtooth function | / | / / / |/ / --/----/----/-- / /| / / / | / | Limit x to the half-open interval [-r, r).

Prototype

pub fn wrap(x: anytype, r: anytype) @TypeOf(x)

Example

 test wrap {
    // Within range
    try testing.expect(wrap(@as(i32, -75), @as(i32, 180)) == -75);
    try testing.expect(wrap(@as(i32, -75), @as(i32, -180)) == -75);
    // Below
    try testing.expect(wrap(@as(i32, -225), @as(i32, 180)) == 135);
    try testing.expect(wrap(@as(i32, -225), @as(i32, -180)) == 135);
    // Above
    try testing.expect(wrap(@as(i32, 361), @as(i32, 180)) == 1);
    try testing.expect(wrap(@as(i32, 361), @as(i32, -180)) == 1);

    // One period, right limit, positive r
    try testing.expect(wrap(@as(i32, 180), @as(i32, 180)) == -180);
    // One period, left limit, positive r
    try testing.expect(wrap(@as(i32, -180), @as(i32, 180)) == -180);
    // One period, right limit, negative r
    try testing.expect(wrap(@as(i32, 180), @as(i32, -180)) == 180);
    // One period, left limit, negative r
    try testing.expect(wrap(@as(i32, -180), @as(i32, -180)) == 180);

    // Two periods, right limit, positive r
    try testing.expect(wrap(@as(i32, 540), @as(i32, 180)) == -180);
    // Two periods, left limit, positive r
    try testing.expect(wrap(@as(i32, -540), @as(i32, 180)) == -180);
    // Two periods, right limit, negative r
    try testing.expect(wrap(@as(i32, 540), @as(i32, -180)) == 180);
    // Two periods, left limit, negative r
    try testing.expect(wrap(@as(i32, -540), @as(i32, -180)) == 180);

    // Floating point
    try testing.expect(wrap(@as(f32, 1.125), @as(f32, 1.0)) == -0.875);
    try testing.expect(wrap(@as(f32, -127.5), @as(f32, 180)) == -127.5);

    // Mix of comptime and non-comptime
    var i: i32 = 1;
    _ = &i;
    try testing.expect(wrap(i, 10) == 1);

    const limit: i32 = 180;
    // Within range
    try testing.expect(wrap(@as(i32, -75), limit) == -75);
    // Below
    try testing.expect(wrap(@as(i32, -225), limit) == 135);
    // Above
    try testing.expect(wrap(@as(i32, 361), limit) == 1);
}

Source

  pub fn wrap(x: anytype, r: anytype) @TypeOf(x) {
    const info_x = @typeInfo(@TypeOf(x));
    const info_r = @typeInfo(@TypeOf(r));
    if (info_x == .int and info_x.int.signedness != .signed) {
        @compileError("x must be floating point, comptime integer, or signed integer.");
    }
    switch (info_r) {
        .int => {
            // in the rare usecase of r not being comptime_int or float,
            // take the penalty of having an intermediary type conversion,
            // otherwise the alternative is to unwind iteratively to avoid overflow
            const R = comptime do: {
                var info = info_r;
                info.int.bits += 1;
                info.int.signedness = .signed;
                break :do @Type(info);
            };
            const radius: if (info_r.int.signedness == .signed) @TypeOf(r) else R = r;
            return @intCast(@mod(x - radius, 2 * @as(R, r)) - r); // provably impossible to overflow
        },
        else => {
            return @mod(x - r, 2 * r) - r;
        },
    }
}  