I am studying the following function:
inline xint dtally(xint x)
{
xint t = 0;
while (x) t += 1 << ((x % 10) * 6), x /= 10;
return t;
}
I just want to know what makes this feature i.e. which computes and stored in the variable t.
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5gon12eder
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Kevin
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3What do you mean by "what makes this feature"? – Scott Hunter Nov 29 '14 at 03:39
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@Deduplicator - yup, just went and checked. Comment rescinded. – Carl Norum Nov 29 '14 at 03:45
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1what is xint? If we knew that detail, then we could answer your question. – user3629249 Nov 29 '14 at 06:00
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That comma operator makes me cry. I hope you didn't find this in production code. If so, please tell us, so we can avoid that guy. – Jens Gustedt Nov 29 '14 at 09:30
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This function is probably bugged (unless you are on ILP64 system), change `1` to `(xint)1` – M.M Feb 18 '15 at 21:42
1 Answers
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This counts the number of base 10 digits in the number x in t, separated by 6-width bit fields.
Note that each shift length is a multiple of 6. So if a digit is 0 the shift is 0, if the digit is 1 the shift is 6, if the digit is 9 the shift is 54, and so forth.
The reason 6 is used I think is so it fits under 64 bits.
simonzack
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The count of each possible base 10 digit in x, i.e., each 6-bit wide field in the output should hold the count of the digits corresponding to that offset in x. Bits 0-5 holds the number of 0's, bits 6-11 the number of 1's, 12-17 the number of 2's, etc. – tvanfosson Nov 29 '14 at 03:52