Saturated Arithmetic

In general binary operation that 11111111（255）+00000001（1）＝100000000（256）

The operation result will be 0 for 8 bit Adder, because the processor is 8 bits only.

If a processor support saturated arithmetic, 255+1 would be 255 (stop at max or min value), and it would not overflow or underflow.


Reference: 
http://www.techbang.com/posts/10678-fully-understand-arm-processors-cisc-and-risc-are-what-history-structure-a-see-through-the-computer-96-issues-cover-story-the-king?page=2

LITTLE_ENDIAN and BIG_ENDIAN

The keywords LITTLE_ENDIAN and BIG_ENDIAN could specify store order in memory.

If there is a two byte data in memory, Ex: long d=0x12345678

It would be store as the order as below table.

	big-endian	little-endian
0x0000	0x12	0x78
0x0001	0x34	0x56
0x0002	0x56	0x34
0x0003	0x78	0x12

What different ?

for some CPU：

• INTEL X86、DEC VAX use LITTLE-ENDIAN
• HP、IBM、MOTOROLA 68K use BIG-ENDIAN
• POWERPC support both，called BI-ENDIAN

Bitmap Format

Note how to read bitmap data
Reference from http://crazycat1130.pixnet.net/blog/post/1345538

-----------------------------

Overview Bitmap Byte File

bitmap file make up of four parts

• Bitmap File Header
• Bitmap Info Header
• Color Table (Palette)
• Bitmap Array

All words was shown in little-endian mode.

It's mean if value is 0x1234, you will look it display 0x3412.

example shown as a 8X8 pixels all fill red color bitmap file

Bitmap File Header
0000h - 0001h : Identifier  ('BM') [1]
0002h - 0005h : File Size (byte)

0006h - 0009h : Reserved

000Ah - 000Dh : Bitmap Data Offset

Example: 

 

 

  

0000	42	Identifier BM 42H=66D='B' , 4DH=77D='M'
0001	4D
0002	F6	because Little-Endian, so writing F6000000H File Size 246 byte F6H=246D Header 54 + Content 192 (8 X 8 X 3) = 246
0003	00
0004	00
0005	00
0006	00	Reserved
0007	00
0008	00
0009	00
000A	36	Bitmap Data Offset 54 byte It's also mean the size of file header
000B	00
000C	00
000D	00

 

Annotations

【１】This field includes verious code for identify type of bitmap：
　　　　'ＢＭ'　－　Windows 3.1x, 95, NT, ...　　　　
        'ＢＡ'　－　OS/2 Bitmap Array　　　　
        'ＣＩ'　－　OS/2 Color Icon　　　　
        'ＣＰ'　－　OS/2 Color Pointer　　　　
        'ＩＣ'　－　OS/2 Icon　　　　
        'ＰＴ'　－　OS/2 Pointer

to be continue...