Shulou(Shulou.com)06/03 Report--

[1] Original code, complement code and complement code are the coding methods for storing a specific number by the machine.

original code

[2] The original code is the absolute value of the sign bit + the true value, the first bit represents the sign bit, and the remaining bits represent the value.

For example:

An 8-bit binary

0000 0001 (1 original code)

1000 0001 (-1 original code)

8-bit binary representation range is

1111 1111-0111 1111（-127，127）

complement

The complement of a positive number is itself, and the complement of a negative number is based on its original code, with the sign bit unchanged and the rest inverted.

that is

0000 0001 (1 original code)---The complement is the same 0000 0001 (1 complement)

1000 0001 (-1 original code)---inverted code symbol bit unchanged, the rest of the inverted 1111 1110 (-1 inverted code), this number can not see what is represented, need to be converted to the original code to see.

complement

The complement of a positive number or itself,

The complement of a negative number is based on the original code, or the complement of the final +1.

[Summary]

Positive--complement (self)--complement (self)

Negative--complement (sign bit unchanged, rest inverted)--complement (complement +1)

[Example: ]

byte b = (byte) 130;

b = ?

[Analysis]

1. All operations in the computer are complementary.

2, calculate the binary data, 130 (default int type 4 bytes), that is, 1000010 (1 byte)

4-bit byte complement is:

000000 0000000 0000000 1000010 (positive-negative-original)

byte Truncate a byte, i.e.(1000010)---(complement)

3, complement to complement code 1000001

4. Reverse code to original code 1 111110 (-126)

[Expansion]

Here we analyze

byte b = (byte) 130;

b = -126;(byte-128: artificially specified-0 is-128----127)

Which means it's a loop, which means

127（127）

128 （-128）

129（-127）

130（-126）

131（-125）

.....

400（-112）

Calculation idea:

From-128--127 to 256

400-256=144（-112）

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