Function readVarInt [src]

Reads an integer from memory with size equal to bytes.len. T specifies the return type, which must be large enough to store the result.

Prototype

pub fn readVarInt(comptime ReturnType: type, bytes: []const u8, endian: Endian) ReturnType

Parameters

ReturnType: typebytes: []const u8endian: Endian

Example

 test readVarInt {
    try testing.expect(readVarInt(u0, &[_]u8{}, .big) == 0x0);
    try testing.expect(readVarInt(u0, &[_]u8{}, .little) == 0x0);
    try testing.expect(readVarInt(u8, &[_]u8{0x12}, .big) == 0x12);
    try testing.expect(readVarInt(u8, &[_]u8{0xde}, .little) == 0xde);
    try testing.expect(readVarInt(u16, &[_]u8{ 0x12, 0x34 }, .big) == 0x1234);
    try testing.expect(readVarInt(u16, &[_]u8{ 0x12, 0x34 }, .little) == 0x3412);

    try testing.expect(readVarInt(i8, &[_]u8{0xff}, .big) == -1);
    try testing.expect(readVarInt(i8, &[_]u8{0xfe}, .little) == -2);
    try testing.expect(readVarInt(i16, &[_]u8{ 0xff, 0xfd }, .big) == -3);
    try testing.expect(readVarInt(i16, &[_]u8{ 0xfc, 0xff }, .little) == -4);

    // Return type can be oversized (bytes.len * 8 < @typeInfo(ReturnType).int.bits)
    try testing.expect(readVarInt(u9, &[_]u8{0x12}, .little) == 0x12);
    try testing.expect(readVarInt(u9, &[_]u8{0xde}, .big) == 0xde);
    try testing.expect(readVarInt(u80, &[_]u8{ 0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0, 0x24 }, .big) == 0x123456789abcdef024);
    try testing.expect(readVarInt(u80, &[_]u8{ 0xec, 0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe }, .little) == 0xfedcba9876543210ec);

    try testing.expect(readVarInt(i9, &[_]u8{0xff}, .big) == 0xff);
    try testing.expect(readVarInt(i9, &[_]u8{0xfe}, .little) == 0xfe);
}

Source

  pub fn readVarInt(comptime ReturnType: type, bytes: []const u8, endian: Endian) ReturnType {
    assert(@typeInfo(ReturnType).int.bits >= bytes.len * 8);
    const bits = @typeInfo(ReturnType).int.bits;
    const signedness = @typeInfo(ReturnType).int.signedness;
    const WorkType = std.meta.Int(signedness, @max(16, bits));
    var result: WorkType = 0;
    switch (endian) {
        .big => {
            for (bytes) |b| {
                result = (result << 8) | b;
            }
        },
        .little => {
            const ShiftType = math.Log2Int(WorkType);
            for (bytes, 0..) |b, index| {
                result = result | (@as(WorkType, b) << @as(ShiftType, @intCast(index * 8)));
            }
        },
    }
    return @as(ReturnType, @truncate(result));
}  