Author: Gerd Isenberg
Date: 07:34:27 02/28/06
Go up one level in this thread
Yes, your approach is indeed also a nice trick to ripple the carry through
unwanted bits.
1.) or with the complement of the original set (d) to set all unwanted bits, so
that a possible overflow walks trough
2.) increment and ripple the carry through unwanted bits
3.) reset all unwanted bits by anding with the original set (d)
Shame that i don't found it by myself ;-(
n = ((n | ~d) + 1) & d;
due to the definition of the Two's complement == One's complement plus one,
it becomes:
n = ((n | (-d-1)) + 1) & d;
Now it looks like the "or" may be simply replaced by add ;-)
n = (n-d) & d;
Nice algebra!
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