Function reverse [src]

In-place order reversal of a slice

Prototype

pub fn reverse(comptime T: type, items: []T) void

Parameters

T: typeitems: []T

Example

 test reverse {
    {
        var arr = [_]i32{ 5, 3, 1, 2, 4 };
        reverse(i32, arr[0..]);
        try testing.expectEqualSlices(i32, &arr, &.{ 4, 2, 1, 3, 5 });
    }
    {
        var arr = [_]u0{};
        reverse(u0, arr[0..]);
        try testing.expectEqualSlices(u0, &arr, &.{});
    }
    {
        var arr = [_]i64{ 19, 17, 15, 13, 11, 9, 7, 5, 3, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18 };
        reverse(i64, arr[0..]);
        try testing.expectEqualSlices(i64, &arr, &.{ 18, 16, 14, 12, 10, 8, 6, 4, 2, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 });
    }
    {
        var arr = [_][]const u8{ "a", "b", "c", "d" };
        reverse([]const u8, arr[0..]);
        try testing.expectEqualSlices([]const u8, &arr, &.{ "d", "c", "b", "a" });
    }
    {
        const MyType = union(enum) {
            a: [3]u8,
            b: u24,
            c,
        };
        var arr = [_]MyType{ .{ .a = .{ 0, 0, 0 } }, .{ .b = 0 }, .c };
        reverse(MyType, arr[0..]);
        try testing.expectEqualSlices(MyType, &arr, &([_]MyType{ .c, .{ .b = 0 }, .{ .a = .{ 0, 0, 0 } } }));
    }
}

Source

  pub fn reverse(comptime T: type, items: []T) void {
    var i: usize = 0;
    const end = items.len / 2;
    if (backend_supports_vectors and
        !@inComptime() and
        @bitSizeOf(T) > 0 and
        std.math.isPowerOfTwo(@bitSizeOf(T)))
    {
        if (std.simd.suggestVectorLength(T)) |simd_size| {
            if (simd_size <= end) {
                const simd_end = end - (simd_size - 1);
                while (i < simd_end) : (i += simd_size) {
                    const left_slice = items[i .. i + simd_size];
                    const right_slice = items[items.len - i - simd_size .. items.len - i];

                    const left_shuffled: [simd_size]T = reverseVector(simd_size, T, left_slice);
                    const right_shuffled: [simd_size]T = reverseVector(simd_size, T, right_slice);

                    @memcpy(right_slice, &left_shuffled);
                    @memcpy(left_slice, &right_shuffled);
                }
            }
        }
    }

    while (i < end) : (i += 1) {
        swap(T, &items[i], &items[items.len - i - 1]);
    }
}  