The valid number of float is seven-bit how to get it out

The following is from Csdn netizen xian_wwq Answer (http://bbs.csdn.net/topics/390874239):

Float
1bit (sign bit) 8bits (digit digit) 23bits (trailing digit)
Precision is determined by the number of bits in the mantissa.
float:2^23 = 8388608, altogether seven bits, which means that there can be up to 7 significant digits,
But the absolute guarantee is 6 bits, also namely the float precision is 6~7 bit valid number;

The valid number of float is seven-bit how to get it out