Supplied character codes

An unsigned byte is 01000001, with weights 128, 64, 32, 16, 8, 4, 2, 1. What decimal value does it represent?

Only the weights of the 1 digits contribute

Characters have assigned numbers

Text can be represented by mapping characters to numbers. Unicode supplies assigned numbers called code points; an encoding such as UTF-8 determines the stored bytes

Upper-case and lower-case letters have different code points. A space is also a character even though it leaves a blank gap

Use the supplied subset below rather than memorising codes. All its code points are below 128; UTF-8 stores each of these particular characters in one byte with the same unsigned value

Read the exact row

Use only the supplied character table. These characters have code points below 128, so UTF-8 represents each one as a single byte with the same unsigned value

What decimal code point does the table assign to Upper-case M?

Locate the row labelled Upper-case M

Its decimal code point is 77; the number names this character in the supplied mapping

Preserve letter case

Select upper-case M and note its code 77 and eight bits. Predict which bit changes for lower-case m, code 109, then select it and compare. Try the other listed characters without assuming that every case change follows the same rule

For this supplied pair, which bit changes when M with code 77 becomes m with code 109?

Character, code point, byte

First identify the exact character in the table and read its decimal code point

For the supplied subset, use that number as the unsigned byte value, then construct its eight binary digits

Keep the encoding rule explicit. The same bit pattern can have other meanings when a different representation rule is used

Encode punctuation

Use only the supplied character table. These characters have code points below 128, so UTF-8 represents each one as a single byte with the same unsigned value

Represent this character: Question mark ?

Use an unsigned 8-bit binary representation: each position contains 0 or 1, and there is no sign bit

Write exactly 8 binary digits, keeping leading zeros when needed, with no spaces or base label

The supplied table assigns Question mark ? the decimal code point 63; in this subset, that is also the byte's unsigned value

Start with 63 and consider the weights from largest to smallest

Use 1 when the weight fits the amount left, then subtract it; otherwise use 0

The 8 digits are 00111111; check their weighted sum: \(32 + 16 + 8 + 4 + 2 + 1 = 63\)

Encode a space

Reverse the two steps

To interpret a byte from this subset, add its binary place contributions to obtain the unsigned value

Find that value in the supplied code-point column and read the character on the same row

A code that is absent from a short table is not automatically invalid; the table may show only a subset. These questions use only its listed entries

Decode a letter

Use only the supplied character table. These characters have code points below 128, so UTF-8 represents each one as a single byte with the same unsigned value

The byte to interpret is 01010010

Read its unsigned value using weights 128, 64, 32, 16, 8, 4, 2, 1 from left to right

Which character does this byte represent under the supplied rule?

The byte's unsigned value is \(64 + 16 + 2 = 82\)

The table maps code point 82 to Upper-case R

Use the declared encoding rule and table together; the bits alone do not say which kind of data is stored

Keep upper and lower case distinct

The supplied text table assigns the character 0 the decimal code point 48. Under its one-byte rule, which byte stores that character? The weights are 128, 64, 32, 16, 8, 4, 2, 1

Encode the character's assigned number, not the number named by the digit

Do not extend the subset rule to all text

Unicode includes far more characters than the eight examples in this table. A code point and its encoded bytes are related but are not always the same number

For example, the character é has decimal code point 233. UTF-8 stores it as two bytes with unsigned values 195 and 169, not as one byte with value 233

Some displayed symbols can involve more than one code point. Counting visible symbols is therefore not a general method for finding file size

For é, the supplied facts are: decimal code point 233, UTF-8 byte values 195 and 169. How many bits are in those two bytes, using eight bits per byte?

Count the stored bytes, not the digits in the code point

Keep the mapping and encoding separate

Find the exact character, including case or a space, in the supplied mapping

Apply the stated encoding rule before converting a byte value to or from binary

The single-byte rule applies to the supplied Basic Latin subset, not to all Unicode text