作者executor1107 (口责.我受够了)
看板NSYSU-CSE97
标题[分享] [计概] [Chapter 3.4~3.5] 随手整理
时间Sun Dec 12 14:24:58 2004
3.4什麽时候会用到实在没概念
有人能说一下吗?
Representation:
To represent a number in Execess, use the following procedure:
1. Add the magic number to the integer.
2. Change the result to binary and 0s so that there is a total of N bits.
Interpretation:
To interpret a number in Execess, use the following procedure"
1. Change the number to decimal.
2. Subtract the magic number from the interger.
感觉是一种转换过程?加密解密?...(好像还没那麽高级吧XD)
Convert the fraction to binary:
总而言之就是乘2再取第一位就是了(或许有错?)
0.125*2=>0.250*2=>0.500*2=>1.000
0 0 1
不过要是0.35呢?
0.35*2=>0.70=>1.4=>?
0 1
Normalize实在又臭又长
sign、exponent、matissa是要注意的
power of exponent代表的电脑能处理的数字的大小
matissa是由unsigned的型式存取的
After Normalized
Store in 2 case(Made by IEEE):
Excess_127:
sign exponent mantissa
1 8 23
1 11 52
Floating-point interpretation for single precision:
The following procedure interprets a 32-bit floating-point number stored in
memory.
1. Use the leftmost bit as the sign.
2. Change the next 8 bits to decimal and subtract 127 from it. This is the
exponent
这边我有点问题.为啥要subtract exponent所容纳的位元的signed max positive number?
像是8 bits就 subtract 127,5 bits就subtract 16?
是为了表达储存的问题吗?为了exponent部份不用考虑到negative的部份?
3. Add 1 and a decimal point to the next 23 bits. You can ignore any extra 0s
at the right.
4. Move the decimal point to the position using the value of exponent.
5. Change the whole part to decimal.
6. Change the fraction part to decimal.
7. Combine the whole and the fraction parts.
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