That is a semi-correct calculation of the wrong number. Base45 does not use all 45 characters in every slot. It goes 16 bits at a time, so the character storing the upper bits only has 2^16/45^2 = 33 possible values.
The most straightforward way to measure efficiency is to see that base45 takes 32 source bits, and encodes them into 33 bits. The way you're calculating, that's only 50%
But the better way to calculate efficiency is to take the log of everything (in other words, count how many bits are needed). Numeric is log(1000)/log(1024) which is 99.7%. Alphanum is 99.9%. Base45 is 97%.
And I don't know where that kanji number came from. It stores 13 bits at a time, mapping to 8192 shift-JIS code points, and the vast majority of them are valid. It's pretty efficient.
That is a semi-correct calculation of the wrong number. Base45 does not use all 45 characters in every slot. It goes 16 bits at a time, so the character storing the upper bits only has 2^16/45^2 = 33 possible values.
The most straightforward way to measure efficiency is to see that base45 takes 32 source bits, and encodes them into 33 bits. The way you're calculating, that's only 50%
But the better way to calculate efficiency is to take the log of everything (in other words, count how many bits are needed). Numeric is log(1000)/log(1024) which is 99.7%. Alphanum is 99.9%. Base45 is 97%.
And I don't know where that kanji number came from. It stores 13 bits at a time, mapping to 8192 shift-JIS code points, and the vast majority of them are valid. It's pretty efficient.